On my car the honest answer turned out to be more interesting than either, and it took two ignition tables and a dyno sheet to see it. The short version: E85 buys boost and it buys ignition timing, and depending on where you look in the rev range you can measure both, one, or neither.

Configuration

Status: Verified

• 2JZ-GTE VVTi, 3,353 cc, 9.5:1 static compression
• Kelford T202-D camshafts, 272°/278° advertised
• Pulsar G42-1200, 73 mm compressor, T4 divided 1.15 A/R
• Emtron KV12, firmware 2.20.22, flex fuel with an ethanol content sensor
• Twelve CP1000 injectors, staged, on a 4 bar 1:1 rising rate regulator. That fuel system is what makes 2.8 bar possible at all, and it is covered separately in Twelve Small Injectors Instead of Six Big Ones
• ZF 8HP70, 5th gear, 1.285:1
• Dynojet, WinPEP 8, uncorrected, 6 March 2026 at SRD Tuning
• Both runs: same session, same equipment, same correction factor

The two runs

200 whp apart. The obvious reading is that E85 is worth 200 whp. It isn’t, and the two runs weren’t at the same boost, so any straight comparison between them is measuring two things at once.

What the ignition tables say

Two main ignition tables, same axes, one for each fuel. Comparing them cell by cell gives a much cleaner answer than the dyno does.

Below 100 kPa, the two tables are identical. Not similar. The same numbers in every cell.

That is deliberate. Off boost the car runs the same timing regardless of what is in the tank, so it idles the same, pulls away the same and behaves the same in traffic on either fuel. A car that drives differently depending on what you last filled it with is a car you have to think about, and this build is meant to be one you don’t.

Above 100 kPa they separate, and they separate by a remarkably consistent amount:

Four to five degrees, right across the boosted region, holding all the way to the limiter. That is what E85 actually bought in this calibration, and it is a separate thing from the extra boost.

Separating the two effects

To a first approximation, mass flow through an engine scales with manifold pressure. So if you know the pressure ratio between two runs, you know roughly how much of the power difference is just boost.

381 kPa against 311 kPa is a pressure ratio of 1.225. Anything above that is coming from somewhere other than pressure.

At peak torque, 881.0 against 688.6 lb ft is a ratio of 1.279. That is roughly four percent more than pressure alone explains. That four percent is the timing.

At peak power, 1,113.9 against 914.2 whp is a ratio of 1.219. Slightly below the pressure ratio. The timing advantage is still sitting in the table, four to five degrees of it, but it has stopped turning into power.

Why the advantage disappears at the top

Status: Working conclusion

The working explanation is the turbo. At 2.8 bar the G42-1200 is at or near the limit of what it can flow, so the E85 run stops gaining before the engine does. The pump run at 2.1 bar still has compressor headroom, which is why it makes its peak power 720 rpm further up the rev range, at 7,940 against 7,220.

That looks backwards until you think about it. The lower boost run revs out further because it hasn’t run out of compressor yet.

I can’t prove it. Turbo shaft speed isn’t logged on this car and there is no exhaust manifold pressure sensor, so I can distinguish neither the compressor side nor the turbine side from the data I have. It is a working conclusion, and it stays one until there is a sensor behind it.

What this means if you’re deciding on flex fuel

The useful conclusion isn’t the 200 whp. It’s where the 200 whp comes from and where it doesn’t.

If you are already boost limited by your turbo, E85’s timing advantage will show up as mid range torque and very little else at the top. You will feel it on the road far more than you will see it on a dyno sheet, because the road is where mid range lives.

If you have compressor headroom left, E85 lets you use it, and then you get both.

And if somebody quotes you a fuel-to-fuel power comparison without telling you the boost on each run, the number means nothing. Two runs at different pressures measure two variables. You cannot attribute the difference to the fuel unless you hold the pressure constant, or do what I have done here and work out how much of it pressure alone would explain.

The experiment I haven’t run

The clean version of this test is both fuels at the same boost. Set 2.1 bar, run pump, run E85, and the entire difference is the timing with nothing else in the way.

That’s a dyno session I haven’t had, and until I do, the four percent figure above is arithmetic rather than a direct measurement. When it happens it goes on this page and if the number is different I will say so.

The 881 lb ft in the table above is not the highest figure from that session. A fourth run reached 901 lb ft and found the limit of the gearbox instead: Where the Stock ZF 8HP70 Gives Up. Engine torque has been capped at 880 lb ft ever since, which is why the E85 figure is where it is.

Full specification, both dyno sheets and the measurement conditions are on the Supra project page.

If you have run the same engine on both fuels at matched boost and have the numbers, I would like to see them. Same boost, same dyno, same session. It is a surprisingly rare test.

The post What E85 Actually Buys: Boost, Timing, and Where the Advantage Vanishes first appeared on BlownByTwins.

I have read the whole thing and responded. What follows is what it actually says, rather than what the internet has decided it says, because the two are some distance apart.

What is actually being proposed

At the moment there is a gap. New vehicles have to meet the Euro standard in force when they are built and registered. Once they are on the road, the rules that keep them at that standard, in regulation 61A of the Road Vehicles (Construction and Use) Regulations 1986, were only ever updated as far as Euro 4 and Euro V. Anything built to Euro 5, Euro 6 or Euro VI has no ongoing legal requirement to keep its emissions control system working.

DfT wants to close that gap by requiring vehicles to keep meeting the standard they were built to, for life. Enforcement would run through existing sections of the Road Traffic Act 1988, section 42 for using a non compliant vehicle, section 75 for alterations to vehicles, and section 76 for fitting or supplying unsuitable parts. Penalties on conviction in the magistrates’ court run from £1,000 to unlimited fines. DVSA would enforce.

The evidence base is worth reading rather than dismissing. A roadside remote sensing study of over 94,000 vehicles across several UK cities found that fewer than one in ten passenger cars met the official nitrogen oxide limits, and that roughly two thirds of Euro 5 and Euro 6 diesel cars were emitting more than three times the level allowed. DVSA’s market surveillance unit logged 331 intelligence reports relating to emissions modifications in 2024, and DfT suspects that is a small fraction of the actual activity.

Which vehicles it applies to

This is the part most people have got wrong, and it matters.

Regulation 61A applies to vehicles first used on or after 1 January 2001. The proposal extends the standards it covers, up to Euro 6 and Euro VI, rather than extending the date backwards. On the most natural reading, a 1997 Supra, a 1999 R34 or anything else registered before 2001 sits outside this entirely. My R35 is squarely inside it. So is every 2001 onwards project.

I say most natural reading because the operative sentence in the consultation refers to all road vehicles in-use in GB from 1 January 2001, which is not the same test as first used on or after that date. Those two phrasings produce very different scopes, and the second would pull pre 2001 cars into the regime for the first time. That is one of the things I have asked DfT to nail down.

Motorcycles are a separate issue. Regulation 61A has never applied to category L vehicles. DfT proposes to include them, while stating in the same section that it has limited analytical evidence specific to in-use emissions from motorcycles and could not identify a clear reason to exclude them. Extending a criminal prohibition to a whole vehicle category because no argument against it was found is the wrong way round.

The four modifications DfT says are always illegal

• Removal or deletion of diesel particulate filters, or gasoline particulate filters on petrol vehicles
• Removal of three way catalysts, often accompanied by alteration or removal of sensors and sometimes ECU remapping
• Manipulation of SCR and diesel exhaust fluid systems, the AdBlue delete
• Manipulation of EGR systems, whether physically or by remapping

DfT is explicit that it is not trying to ban modification generally. The document says vehicle alteration is a legitimate practice embraced by tuners, repairers and enthusiasts worldwide, and that it is not seeking to stop people fitting generic rather than OEM parts. It also says that the legality of a modification, hardware or software, depends primarily on how it affects the standard the vehicle was legally built to.

That is an outcome based test, and I have no argument with it. If the car meets its limits, it meets its limits.

Where the drafting contradicts itself

The consultation asks whether a modification should be unlawful where it is a known and proven fact that it will always result in illegal levels of emissions. The word doing the work there is always.

Three of the four items survive that test. SCR, DEF and EGR systems are manipulated in order to defeat them, not to replace them. Delete a DPF and you have deleted a DPF.

The catalyst item does not survive it. Removal of three way catalysts describes a physical act, not an emissions outcome. It catches deleting a cat and running nothing, which should absolutely be illegal. It equally catches replacing a failed or obsolete original cat with a modern aftermarket one, which is ordinary repair, and which on a properly calibrated closed loop setup routinely meets or beats the original. That is not a case where illegal emissions always result. It is a case where they do not result at all.

The fix costs DfT nothing. Describe the harm rather than the component: removal of a three way catalyst without replacement by a catalytic converter that maintains the emissions limits applicable to the vehicle. Deletion stays illegal. Repair stays legal. The same wording change applies to the DPF and GPF item.

The durability problem

This one is on the face of the consultation, and I think it is the strongest objection available.

Manufacturers have to demonstrate that their emissions technology performs as expected for 100,000 km or five years, whichever comes sooner. Separate pollution control devices, catalytic converters among them, have to last 160,000 km.

The proposal puts an obligation on owners with no durability ceiling at all. An owner would carry indefinitely a standard the manufacturer only ever had to guarantee to a defined limit. A 2003 car on 180,000 miles with an original catalyst that has simply aged is not a vehicle anybody modified. It is a vehicle that got old, which is what vehicles do.

What the consultation does not answer

• There is no mechanism by which you can establish that you are compliant. No certificate, no list of authorised testing bodies, no independent appeals route. The proposal creates an offence without creating a way to prove you are not committing it.
• Alternative fuels are not mentioned anywhere. If a car is converted to E85, is compliance demonstrated on E85 or on the fuel it originally ran? How is a flex fuel car assessed when ethanol content changes between fills? Nothing.
• The legal weight of an MOT emissions pass is not addressed. DfT acknowledges the annual roadworthiness check is limited in what it can assess, which leaves owners relying on a test that may not be the test.
• Burden of proof is not stated. Does DVSA have to establish the standard applicable to your specific vehicle and then prove it exceeds that, or is the presence of aftermarket parts enough to start the argument?

This lands on the industry before it lands on owners

DfT says enforcement will likely focus upstream, on the practices behind illegal modifications, because roadside and annual testing can only assess so much. Read that properly. The people most exposed are not individual owners with modified cars. They are mapping outfits, exhaust fabricators, remap resellers and workshops, who under section 76 can be prosecuted for fitting or supplying unsuitable parts.

Which is exactly why the missing compliance mechanism matters. If a business is expected to know whether a configuration is legal before it hands the keys back, somebody has to define the test it applies.

How to respond

The quickest route is the online response form, which lets you save and come back to it. You can also email your response to ivs.consult@dft.gov.uk. The full consultation document is here. It closes at 11:59pm on Sunday 6 September 2026.

If you do respond, answer the questions they actually asked. The consultation has a defined question set and responses get coded against it. A long free text essay that does not map to those questions is much easier to summarise into nothing. I know this because I sent the essay first.

The points I would make, if you want somewhere to start:

• Agree that a modification which always produces illegal emissions should be unlawful, then object that catalyst replacement does not meet that test and the wording should describe the outcome rather than the component
• Ask for the durability obligation on owners to be reconciled with the 100,000 km and 160,000 km limits placed on manufacturers
• Ask for a compliance certification route and an appeals process to exist before enforcement begins
• Ask for the 1 January 2001 scope to be stated unambiguously on the face of the instrument
• Say the six month lead-in should be longer, and should start from publication of final technical guidance rather than from the date the legislation passes

Where I have landed

I am not against this. Deleting a cat or a DPF to make a car louder or cheaper to run puts pollution into air that other people breathe, and I do not have a defence for it. The remote sensing numbers are not invented.

My problem is narrower than that. As drafted, one line of this treats replacing a worn out component with a better one exactly the same as removing it and running nothing. That is not an emissions policy, it is a parts policy, and it will not clean up a single mile of air.

I would like to hear from anyone who runs a business doing this work, because you are the ones who need certainty out of it and you are the ones the enforcement is pointed at. Comments are open.

The post The DfT in-use emissions consultation, what it actually proposes first appeared on BlownByTwins.

The answers you find are all secondhand. Someone knows someone whose car makes 900 and it’s fine. Someone else grenaded one at 700. Nobody publishes a number with a trace behind it.

Here’s one. On 6 March 2026 my 8HP70 let go at 901 lb ft, on a dyno, in front of witnesses, with the run on file.

Configuration

Status: Verified

• ZF 8HP70, stock internals, stock torque converter
• CANformance CAN TCU, release v1.1 beta 13
• Emtron KV12 engine management, firmware 2.20.22
• 3.4 litre 2JZ-GTE VVTi, Pulsar G42-1200, OS Giken LSD, 2.93 final drive
• Tyres: Continental SportContact 7, 295/30/19 rear
• Fuel: E85 at 2.8 bar gauge
• Dyno: Dynojet, WinPEP 8, uncorrected, at SRD Tuning
• Gear: 5th, 1.285:1
• Transmission oil temperature: approximately 95°C

Why 5th and not 6th

6th on an 8HP70 is direct drive, 1:1, and would have been the cleaner gear to measure in. It wasn’t available.

With a 2.93 final drive and a 659.6 mm rolling diameter on the 295/30/19, 8,200 rpm in 6th is roughly 216 mph at the roller. That is past the speed ceiling of the dyno. The same rpm in 5th is about 168 mph, which is comfortably inside it.

So the run happened in a reduction gear. The box was not passing engine torque straight through; it was multiplying it by 1.285 on the way to the output shaft. Worth stating plainly, because it changes how the number generalises.

What it looked like

Revs rose. Torque dropped. Run aborted.

That’s the whole signature, and it’s worth sitting with because it is not subtle and it is not ambiguous. Engine speed climbing while measured torque falls means the input side is turning faster than the output side. Something between them is not holding. On a dyno in a fixed gear there is only one candidate.

SRD called it as clutch slip from the cell. No fault code, no warning, no drama. The trace simply diverges and the run stops being a measurement of the engine.

It is on the sheet as the blue line: 1,095.89 whp at 6,710 rpm, 901.33 lb ft at 5,700 rpm, and then a trace that stops climbing and ends early. Every other run on that sheet carries on to 8,200 rpm.

Why the temperature matters

Wet clutch capacity falls as fluid heats. Publish a slip figure from a box at 130°C after ten back to back pulls and you have measured heat soak, not capacity.

This was at roughly 95°C, comfortably inside the fluid’s operating range and nowhere near tMax. Normal hot running, not a cooked gearbox. That is what makes the number worth quoting.

The qualification nobody makes

Status: Working conclusion

Clutch capacity is clamp load. Clamp load is line pressure. Line pressure is commanded by the transmission controller.

So what I measured is not “the 8HP70 holds 901 lb ft”. It is “this 8HP70 held 901 lb ft of engine torque in 5th, at the line pressure this controller commanded, at this temperature.” Change the controller and the number can move.

That distinction is not academic. It is the reason a straight answer to “what will an 8HP hold” doesn’t exist, and it is why the forum numbers scatter so widely. Different controllers, different pressure strategies, different gears, different results, all reported as though the gearbox were the only variable.

Where the limit applies

Because the measurement came from a reduction gear, it does not transfer evenly across the box.

Below 5th the ratios multiply harder: 1.67, 2.11, 3.14, 4.71. For the same engine torque the internals see progressively more, so 1st through 4th are the exposed end. The torque model reduces demand there, which means those gears never see the full number. That is handled in calibration rather than hoped for.

Above 5th the ratios go the other way: 1.00, 0.84, 0.67. Less multiplication, and in the top two an overdrive. On paper the model would allow more engine torque in 6th, 7th and 8th than it does in 5th, and I have chosen not to take it.

880 lb ft is a global cap, not a per gear one. The only gear I have a measured failure point for is the one I broke it in, and I am not interested in discovering whether 890 slips in top at motorway speed.

A per gear torque map is the correct answer eventually. It needs a measured limit for each gear, and getting those means deliberately slipping the clutches seven more times. Until then, one number everywhere, set by the one gear I have evidence for.

What we settled on

Torque limited to 880 lb ft. The E85 run on the same sheet peaks at 880.98 lb ft and pulls cleanly to 8,200 rpm at 1,113.9 whp.

So the headline number on the car is not what the engine can make. It is what the gearbox will accept. The 3.4 stroker is torque limited by the transmission, not by the engine, the turbo or the fuel.

A 20 lb ft margin below a known failure point, on a road car that covers long distances, is a sensible trade. I would rather leave torque on the table than rebuild a gearbox on the hard shoulder.

The torque cap is not a blunt limiter. It runs through the same torque model that the traction control uses, reaching for throttle area first and ignition retard second. What that fuel and boost combination is actually worth is covered in What E85 Actually Buys.

What’s next

The 8HP75 and an Emtron TM16 controller, together, and both for the same reason: the car is currently limited by the weakest link in the driveline and that link is known.

The interesting part is that swapping the controller as well as the box separates the two variables. Same engine, same power, same driver, same roads, two different transmission controllers. That comparison does not exist anywhere that I can find, and when it does I will publish both sides of it.

Full specification and the dyno sheet are on the Supra project page. The gearbox installation itself is covered in The Big Single and 8 Speed.

If you have run an 8HP70 past 900 lb ft and it held, or lost one well below it, I would like to know the gear, the controller and the fluid temperature. Those are the three numbers everyone leaves out.

The post Where the Stock ZF 8HP70 Gives Up: 901 lb ft, Measured first appeared on BlownByTwins.

A straight line is the one shape the table physically cannot be.

This isn’t a precision quibble. In the operating band where the engine spends most of its life, meaning idle, overrun, light cruise and the first few percent of tip-in, a linear table over-states flow area by a factor of two to four. Every downstream calculation inherits that error: fuel mass, torque estimation, pedal mapping, and on a drive-by-wire car, the inverse map the controller uses to decide where to put the plate.

This article covers the geometry of why, the compressible flow equations that turn area into mass, what a throttle mass flow (TMF) model does with the result, and a repeatable method for building a table that’s correct rather than convenient.

Part 1: The geometry

The projection

A butterfly valve is a disc on a shaft in a cylindrical bore. Air gets past it through whatever cross-section the disc doesn’t block, viewed along the bore axis.

Set up coordinates: the bore axis is z, the shaft runs along x, and the plate rotates about the shaft. Call the plate’s angle from the bore-normal plane α, and the angle it sits at when hard against the closed stop α₀.

For the plate to seal in a cylindrical bore at angle α₀, it can’t be a circle. The intersection of a cylinder of radius R with a plane tilted at α₀ is an ellipse with semi-axes R and R/cos α₀. So the plate is elliptical, with the long axis running across the shaft.

Project that plate onto the plane normal to the flow at an arbitrary angle α, and you get an ellipse with semi-axes:

• R along the shaft
• R · cos α / cos α₀ across it

Which gives the blocked area directly:

A_blocked = πR² · (cos α / cos α₀)

And therefore:

A_open = πR² · (1 − cos α / cos α₀)

Two sanity checks. At α = α₀ the cosine ratio is 1 and open area is zero, because the plate fills the bore. At α = 90° the ratio is zero, open area equals bore area, and the plate is edge-on. Both correct.

Why it can’t be linear

Differentiate the open area with respect to α:

dA/dα = πR² · sin α / cos α₀

Near the closed position, sin α is small. The area barely moves. Expand the cosine for small openings and you get area growing with the square of the angle, not the first power:

1 − cos α ≈ α² / 2

A quadratic. That’s the whole argument. The throttle plate has to swing through a meaningful angle before it uncovers meaningful area, because at small angles you’re only exposing the thin crescent at the edge of a tilted ellipse.

Put numbers on it. Take an 82 mm bore, a closed angle of 9°, an open stop at 83°, and a throttle position axis that runs 0 to 100% of mechanical travel:

(Bore area 5281 mm². Shaft blockage included, see below. Linear column assumes full scale = bore area.)

The error is worst exactly where it hurts most. A big throttle on a big engine cruises at single-digit TPS. That’s the region where a linear table is out by a factor of four.

The shaft

The shaft blocks area too, but not in the way most people assume. Its projected area is roughly shaft diameter × bore diameter, so call it 8 mm × 82 mm ≈ 656 mm², over 12% of the bore.

But at small openings the shaft is hidden behind the plate’s projection. The plate’s projected ellipse is nearly as wide as the bore, and the shaft sits along its centreline. Shaft blockage only becomes real once the plate has swung far enough that its projection narrows past the shaft width, which on typical geometry is somewhere past 60 to 70°.

So the shaft is irrelevant at idle and dominant at wide-open throttle. If you’ve ever wondered why a throttle body flows meaningfully less than its nominal bore area suggests at WOT, that’s most of the answer.

What the closed-form misses

The clean equation above is a thin-plate, sharp-edged idealisation. Real hardware has:

• Plate thickness. A 2 mm plate at 15° presents a real edge to the flow, not a mathematical line.
• A seal taper or step in the bore at the closed position, common on OEM bodies to control leakage and stop the plate binding.
• A relieved or chamfered plate edge, which changes the effective flow path at small angles specifically.
• Screw heads on the plate face where it’s fastened to the shaft.
• Non-concentricity between the plate’s rotation axis and the bore centreline on some designs.

None of these are worth modelling analytically. Integrate the geometry numerically and stop pretending you have a closed form. The code is fifteen lines and it handles the shaft correctly for free.

import numpy as np

def open_area(alpha_deg, alpha0_deg, bore_d, shaft_d, n=2000):
    """
    Geometric open area of a butterfly valve, by numerical integration.

    alpha_deg  : plate angle from the bore-normal plane (deg); ~90 = fully open
    alpha0_deg : plate angle at the closed stop (deg)
    bore_d     : bore diameter (mm)
    shaft_d    : shaft diameter (mm)

    Returns (area_mm2, fraction_of_bore_area)
    """
    R  = bore_d / 2.0
    a  = np.deg2rad(alpha_deg)
    a0 = np.deg2rad(alpha0_deg)

    # projected plate ellipse: semi-axis R along shaft, R*cos(a)/cos(a0) across
    sx = R
    sy = max(R * np.cos(a) / np.cos(a0), 1e-12)

    g = np.linspace(-R, R, n)
    X, Y = np.meshgrid(g, g)

    in_bore  = (X**2 + Y**2) <= R**2
    in_plate = ((X / sx)**2 + (Y / sy)**2) <= 1.0
    in_shaft = np.abs(Y) <= shaft_d / 2.0

    cell = (2 * R / (n - 1))**2
    area = np.count_nonzero(in_bore & ~in_plate & ~in_shaft) * cell
    return area, area / (np.pi * R**2)


def servo_to_angle(tps_pct, alpha0_deg, alpha_max_deg):
    """Linear travel-to-angle map. Verify this on your own hardware."""
    return alpha0_deg + (tps_pct / 100.0) * (alpha_max_deg - alpha0_deg)


for tps in [0, 1, 2, 3, 5, 8, 12, 20, 30, 45, 60, 80, 100]:
    ang = servo_to_angle(tps, 9.0, 83.0)
    a, f = open_area(ang, 9.0, 82.0, 8.0)
    print(f"{tps:5.1f}%  {ang:5.1f}°  {a:8.1f} mm²  {f*100:5.2f}%")

Servo position is not plate angle

The table’s axis is usually servo or throttle position in percent. That is a percentage of mechanical travel, mapped through the sensor calibration. It is not plate angle, and it is not flow area.

Two things break here routinely:

The zero point. TPS 0% is wherever the sensor was zeroed, which is typically the closed stop. But the closed stop is often set slightly below the sealing angle so the plate loads against it, or slightly above so it doesn’t jam. If your assumed α₀ is a degree out, your area predictions at low TPS are out by a large multiple, because you’re on the steepest part of a quadratic.

The full-scale point. Plates rarely reach 90°. Mechanical stops usually land somewhere between 80° and 86°, and the linkage may not be perfectly linear across the range. On a DBW body with a direct gear train it’s close enough to linear to be usable. Verify rather than assume.

Measure both. Command the throttle to a known position, remove the intake pipe, and measure the plate angle directly. A digital angle gauge against the plate face is good to a few tenths of a degree, which is plenty. Do it at 0%, 100%, and three or four points in between to confirm linearity. This is twenty minutes of work that determines whether everything downstream is right or wrong.

The scaling trap

If a table has been carried over from a different throttle body, check what it was scaled by.

Area scales with the square of diameter. Going from 68 mm to 82 mm:

• Diameter ratio: 82 / 68 = 1.206
• Area ratio: 82² / 68² = 1.454

Scale by diameter instead of area and every entry is 17% low. That’s the obvious error.

The subtler one: even a correctly area-scaled table has the wrong shape. Closed angle, open stop angle, and shaft-to-bore ratio all differ between bodies, and none of them scale with diameter. The same shaft in a smaller bore blocks a larger fraction of it. A table lifted from another throttle body and multiplied by a constant is wrong in a way no single multiplier can fix.

Part 2: From area to mass flow

Geometric area isn’t flow area. Two corrections stand between them.

Discharge coefficient

Real flow through an orifice separates at the edge and forms a vena contracta narrower than the geometric opening. The ratio of actual to ideal flow is the discharge coefficient, Cd.

For a butterfly valve, Cd is a function of plate angle, and to a lesser extent of Reynolds number and pressure ratio. Typical values sit somewhere in the 0.6 to 0.8 range across most of the travel, though published data varies considerably with plate profile and bore geometry. The behaviour at very small openings, where the flow is a thin slot jet past a tilted edge, is the least consistent across sources.

If your ECU exposes a separate Cd or flow-correction table against angle, keep the geometric table geometric and put the empirical correction in the Cd table. Two tables, two jobs, and you can reason about each independently. If it only exposes one “effective area” table, you’re folding Cd into it, which works, but means the table is no longer verifiable against geometry, and you lose the ability to sanity-check it with a ruler and a protractor.

The compressible flow equation

Air through a restriction is compressible. The standard isentropic nozzle relation:

ṁ = Cd · A · (P_up / √(R_s · T_up)) · Ψ(PR)

where PR = P_down / P_up, R_s = 287 J/kg·K, and Ψ depends on whether the flow is choked.

Critical pressure ratio for air (γ = 1.4):

PR_crit = (2 / (γ+1))^(γ/(γ-1)) = 0.528

Subsonic (PR > 0.528):

Ψ = √( (2γ/(γ-1)) · ( PR^(2/γ) − PR^((γ+1)/γ) ) )

Choked (PR ≤ 0.528):

Ψ = √γ · (2/(γ+1))^((γ+1)/(2(γ-1))) = 0.6847

Both expressions agree at PR = 0.528, as they must.

The consequence nobody expects: your throttle is choked at idle

Idle manifold pressure on a healthy engine might be 35 kPa absolute, against roughly 101 kPa ambient upstream. That’s a pressure ratio of 0.35, well below critical.

The throttle is sonic. Flow is at the speed of sound in the gap between plate and bore.

That has a specific and useful consequence: when choked, mass flow depends only on Cd, area, upstream pressure and upstream temperature. Manifold pressure has no influence whatsoever. Ψ is pinned at 0.6847 and stays there.

Which means at idle, the model reduces to:

ṁ = Cd · A · P_ambient / √(R_s · T_up) · 0.6847

Every percent of error in your area table becomes a percent of error in calculated air mass, with nothing to absorb it. There is no MAP feedback, no VE term, no second path. Area is the model.

Work out where choking ends: PR = 0.528 against 101 kPa ambient means MAP = 53 kPa. Anything below that is choked, which covers idle, overrun, and most light-load cruise on a large-displacement engine. A big proportion of normal driving sits in the region where the area table is the sole determinant of calculated airflow.

This is the single strongest reason to get the table right, and the reason area errors show up as idle and cruise fuelling problems specifically.

The boosted case, and why pre-throttle pressure matters

Now put the throttle under boost. Upstream is charge pipe pressure, say 200 kPa absolute; downstream is plenum, say 190 kPa. PR = 0.95. Deeply subsonic, and this is where Ψ gets vicious.

Run the numbers:

A 1% change in pressure ratio produces roughly a 9% change in mass flow. The function is nearly vertical up here.

Which brings us to the thing that decides whether a throttle model can work in boost at all: you must know the pressure upstream of the throttle plate.

Without a pre-throttle sensor, the ECU has to infer it, usually from a modelled pressure drop across the intercooler and pipework, or from a boost target, or by assuming it equals MAP plus some offset. All of those are estimates, and the sensitivity above means a 2 kPa estimation error at part throttle in boost produces a double-digit percentage error in calculated air mass.

Fit the sensor. On a naturally aspirated engine you can argue that ambient is close enough. On a boosted engine running a throttle-based air model, a pre-throttle pressure sensor is not an optional refinement. It’s the difference between a model and a guess.

My own car runs both sides: pre-throttle and post-throttle pressure are each measured, not inferred. On a throttle mass flow model those two sensors are not instrumentation, they are part of the model, and the pressure ratio between them is the term the whole calculation hinges on. Full sensing list is on the specification page.

Note also that the sign of the problem inverts across the throttle range. At small openings the pressure ratio is low, the flow is choked or near-choked, and the model is insensitive to downstream pressure but exquisitely sensitive to area. At large openings in boost the pressure ratio approaches unity, area error matters less, and pressure error dominates. Different regions of the same table fail for different reasons.

Part 3: What the ECU does with it

The throttle mass flow model

A throttle mass flow model, TMF in Emtron’s vocabulary, with equivalents under different names across most modern standalone platforms, computes cylinder air mass from the throttle rather than from the manifold.

Broadly:

1. Throttle position → plate angle (via the servo map)
2. Plate angle → geometric area (via the area table)
3. Area × Cd → effective area
4. Effective area + upstream pressure + upstream temperature + pressure ratio → mass flow through the throttle
5. Mass flow → cylinder filling → fuel

Contrast that with speed density, which computes cylinder air mass from manifold pressure, air temperature, engine speed and a volumetric efficiency table. I first wrote about why that distinction mattered in 2023, when choosing an ECU for the R34, long before I understood how much sat underneath it.

The two models fail in opposite ways, which is precisely why good ECUs run both:

Speed density is accurate in steady state because MAP is a direct measurement of what’s actually in the manifold. It’s late in transients, because the manifold takes time to fill and the sensor reports the result rather than the intent. Stab the throttle and the MAP sensor tells you what happened a few tens of milliseconds ago.

Throttle mass flow is immediate, because the plate moves before the manifold responds, so the model sees the demand as it happens. But it’s an inference stacked on a chain of assumptions: area table, Cd, servo map, upstream pressure. Every one of those is a place to be wrong.

So the ECU blends them: TMF-weighted during transients where response matters, SD-weighted in steady state where accuracy matters, with a handover region between.

Diagnosing the handover

The handover is where calibration errors become visible, and it’s diagnostically valuable for exactly that reason. If your two models disagree, the blend region will show a fuelling discontinuity that tracks the blend weighting rather than any physical parameter.

Log fuel trim, or measured lambda error, against whatever variable drives the blend. Three patterns:

A step at the handover. The two models disagree at that operating point. One is wrong; the trim jumps as authority transfers.

A ramp through the handover. The models disagree by a growing margin across the region. Usually indicates a slope error in one of them, either a VE table with the wrong shape, or an area table with the wrong curvature.

Clean through the handover, but offset either side. Both models share a common error downstream of the blend, such as injector characterisation, a global trim, or fuel pressure.

That third case is where things get interesting, because a common error can hide the first two. Which leads to the diagnostic fork.

The fork: when the symptom contradicts the geometry

Here’s a scenario worth walking through, because it’s a trap.

Suppose you determine your area table over-states area by roughly 3× in the idle band, established from geometry, exactly as above. The model is being told there’s three times as much air going past the plate as there really is.

You’d expect the engine to run rich at idle, and the fuel model to read high.

Now suppose your logs show the opposite: TMF reading around 9% low at idle, with a positive fuel correction propping it up.

Both observations can’t be direct consequences of the same cause. Something else is in the chain. Three branches, all testable:

Branch 1: a global trim is masking the shape error. Somewhere there’s a multiplier, a fuel scaling constant, or a Cd table that was adjusted until mid-range worked. That adjustment is fighting the area error, and the residual at idle is what’s left after the fight. Test: remove or neutralise the compensating term and see whether idle error grows in the direction the geometry predicts. If it does, the geometry diagnosis stands and the trim was a bandage.

Branch 2: the Cd table is pulling the other way. If Cd is populated with values that fall sharply at small openings, it may be cancelling much of the geometric over-statement. Test: multiply the area and Cd tables together and plot the product against angle. That product is what the model actually uses. If the product is close to geometrically correct, the individual tables are wrong but the model isn’t, which means fixing the area table alone will break it.

Branch 3: the axis doesn’t mean what you think. The table may be indexed on plate angle rather than percentage travel; or on a normalised area rather than absolute; or the “servo position” channel may be the commanded target rather than the measured position, which differ during any transient and can differ statically if there’s a calibration offset. Test: command a known position, measure the actual plate angle, and confirm which number the table is being indexed on.

Resolve the fork before changing anything. The failure mode here is correcting the area table on sound geometric grounds, discovering the engine now runs badly, and concluding the geometry was wrong. The geometry isn’t wrong. Something else in the chain was compensating for it, and you’ve now removed one half of a matched pair.

Which is the general rule: compensating errors must be corrected together or not at all. If a wrong area table and a wrong global trim have been co-calibrated to produce acceptable fuelling, fixing either one alone makes the car worse. Identify both, correct both, revalidate.

Part 4: The dual-use trap

On a drive-by-wire car, the throttle area table is usually consumed in two directions.

Forward, for the air model: position → area → mass flow → fuel.

Inverse, for torque-based control: torque demand → required mass flow → required area → target throttle position.

The same table. Read backwards.

That inverse map is not an edge case. It is what every torque-based system on the car leans on. When traction control decides to pull torque and reaches for throttle area as its first actuator, this table is what turns a torque request into a plate position. An area table that is wrong at small openings makes every one of those interventions wrong too.

Three consequences.

Fixing the fuel model changes the pedal

If the table over-states area at small openings, the inverse map under-commands position for a given torque request, because the controller thinks a tiny opening delivers a lot of air, so it asks for a tiny opening. Correct the table and the same pedal input now produces a larger commanded opening.

Which is correct, but it isn’t the same. Tip-in response, idle control authority, cruise position and any part-throttle torque limiter behaviour all shift. Expect to revalidate driveability alongside fuelling, and don’t do it on a road.

Non-monotonicity breaks the inverse map

A table with hand-entered noise, where area at 5% exceeds area at 6%, is merely inaccurate in the forward direction. It’s ill-posed in the inverse direction.

Inverting a non-monotonic function means that for some torque demands, more than one throttle position satisfies the request. Depending on how the solver is implemented, you get target jumps, hunting, or an oscillation whose frequency is set by the controller rather than by anything physical.

Where does hand-entry noise usually live? In the low-percentage cells, because that’s where people have been poking at values trying to fix an idle problem. Which is exactly where idle control and tip-in operate.

Check monotonicity explicitly. It takes one line:

assert np.all(np.diff(area_table) > 0), "Area table is non-monotonic"

If that fails, no amount of downstream tuning will produce stable control.

The table is not a tuning parameter

The strongest reason to build the area table from geometry rather than from fitting: it’s the only table in the chain that has a verifiable, physical, single correct answer.

VE is empirical. Cd is empirical. Injector characterisation is empirical. Geometric flow area is a solid modelling problem with one right answer, computable from four measurements, and it does not change as the engine ages.

Once it’s correct, it’s correct permanently, and every empirical table downstream is being fitted against a fixed truth rather than against another set of assumptions. That’s what makes the rest of the calibration converge instead of chasing itself.

Treating the area table as somewhere to dial in a fuelling problem throws away the one fixed reference point in the entire model.

Part 5: Method

1. Measure the hardware. Bore diameter, shaft diameter, plate thickness. Callipers.
2. Measure the closed angle. Digital angle gauge against the plate face at the closed stop. This number matters more than any other single measurement, because it sets where you sit on the quadratic.
3. Measure the open stop. Same method, throttle commanded to 100%.
4. Verify the servo map. Command 20%, 40%, 60%, 80%; measure the angle at each. Confirm the travel-to-angle relationship is linear before assuming it.
5. Compute the geometric table numerically. Use the code above, at the resolution your ECU’s table supports. Populate the low-percentage region densely, because that’s where the curvature is, and where linear interpolation between widely-spaced breakpoints does the most damage.
6. Check monotonicity. Every cell strictly greater than the one before.
7. Handle Cd deliberately. Separate table if the ECU allows it. If not, decide consciously what Cd assumption you’re folding in and write it down.
8. Identify existing compensating terms before you change anything. Global fuel multipliers, mass fuel corrections, Cd tables, anything that’s been trimmed to make the current calibration work. These come out or get re-derived in the same change.
9. Validate against logs. With the corrected table, TMF and SD should converge in steady state without a compensating pad. That convergence is your proof, not the smoothness of the fuel trim, which can be smooth for the wrong reasons.
10. Revalidate driveability, because you have just changed the inverse map that determines where the plate goes.

Summary

A butterfly valve’s open area grows with the square of plate angle near closed, not linearly. In the idle-to-light-cruise band, a linear table over-states area by two to four times.

Below roughly 53 kPa manifold pressure, the throttle is choked and manifold pressure has no effect on flow at all. Area and upstream pressure are the entire model. Above that, in boost, the flow function is so steep that a 1% pressure ratio error produces a 9% mass flow error, which is why pressure sensors either side of the plate are mandatory rather than optional on a boosted throttle-model car.

The area table is the only table in the air model with a single verifiable correct answer. Build it from geometry, keep the empirical corrections in the tables designed for them, and check it’s monotonic before wondering why the drive-by-wire target is hunting.

And if fixing it makes the engine worse, you’ve found a compensating error, not a mistake in the maths.

This is the first of a series on the Emtron KV12 running a 3.4 litre 2JZ. The torque model that sits on top of this table drives the traction control strategy, and it is also what caps engine torque at the measured limit of the gearbox. Full specification and measurement conditions are on the Supra project page.

If you have built one of these tables from geometry and found the Cd behaviour at very small openings differs from the published ranges, I would like to hear about it. That is the part of this I trust least.

The post Throttle Body Effective Flow Area: Building a Correct Area vs Position Table first appeared on BlownByTwins.

This is now the third failure in 15 months on a £1,400 + VAT product. The car was also away for engine work for around three of those months, so the real-world usage period is even lower than the calendar period suggests.

The issue is simple: the downshift paddle has stopped working again. The larger issue is that the product is now discontinued, and although the adapter is apparently still within warranty, there does not appear to be a replacement hub or a proper repair path available.

UPDATED: 03/07/26: Following publication, Tegiwa offered to accept return of the product. I have also removed direct quotation from private correspondence and paraphrased the supplier’s position instead. The supplier position, as communicated, is that the switch should not be moving, that this may be a design oversight, and that the repair approach given to SRD was to secure it with hot glue. My concern remains that the downshift paddle has repeatedly failed and that the proposed fix appears to be an adhesive workaround rather than a formal manufacturer-supported repair or replacement route.

That leaves the warranty position in a very poor place. A warranty is only useful if there is a practical remedy behind it.

Zestek Downshift Paddle Failure Timeline:

• March 2025: The Zestek steering wheel adapter was purchased as part of the first build.
• May 2025: The downshift paddle failed during the trip to JapFest at Silverstone.
• May 2025: SRD contacted Tegiwa. I was asked to take the car to Tegiwa’s premises in Stoke, where the fault was repaired onsite.
• January 2026: The car was away at SRD for the 3.4 build when the Zestek failed again. Tegiwa advised SRD how to repair it, and it was fixed again.
• June 2026: The downshift paddle failed for a third time. I contacted both Tegiwa and Zestek. Tegiwa said they would speak to Zestek, but after 10 days I had not received a meaningful update. I then posted about the issue on Instagram, after which Tegiwa got back in touch. I still had no direct response from Zestek, despite them having seen the stories.

What Has Failed?

The downshift paddle is no longer working.

That matters because this is not a cosmetic issue or a minor inconvenience. On a paddle-shifted car, the steering wheel controls are part of the core driving interface. A failed downshift paddle affects and detracts from how the car is driven and undermines confidence in the product.

This is also not a one-off failure. The same function has now failed three times in 15 months.

Warranty and Support Position

The adapter is apparently still within warranty. However, Tegiwa have stated that the hub has been discontinued and that they cannot supply anything to fix it or replace it.

That is the core problem.

If a product is discontinued while still inside its warranty period, there still needs to be a credible remedy. That could be a replacement part, a repair, a replacement unit, a credit towards the successor product, or a refund route. At the moment, the position appears to be: there is a warranty, but no available fix or replacement.

That is not good enough for a £1,400 + VAT steering wheel adapter.

The Suggested Fix

Tegiwa asked whether I had attempted to repair it myself. I had not, because I did not want to take the unit apart and risk affecting the warranty position.

They then sent instructions on how to attempt a fix and asked me to let them know how I got on, including whether the switch was the issue.

Tegiwa sent me instructions (above) to fix. They were the instructions.

That is not a proper warranty remedy. It is a self-diagnosis route on a product that has already failed multiple times. If it is the switch, the product has still failed again. If it is not the switch, the problem is worse, because there is apparently no replacement hub or supported repair route available.

Either way, the customer is left with the risk.

Why This Is a Problem

This is not a cheap generic steering wheel accessory. It is a premium adapter costing £1,400 + VAT.

For that money, I would expect durability, support, and a proper warranty route. Instead, I have had:

• three failures in 15 months;
• a repeat failure of the same core control;
• a discontinued product;
• no replacement hub available;
• no direct support from Zestek;
• no clear warranty remedy.

The issue is not just that the paddle has failed. Mechanical and electrical parts can fail. The issue is that it has failed repeatedly, and the support position appears to collapse once the product is discontinued.

Would I Buy Another Zestek Adapter?

Based on my experience, no.

I would not buy another Zestek steering wheel adapter unless the supplier confirmed the following in writing before purchase:

• spare parts are available;
• paddle switches are serviceable;
• the warranty remedy is clear;
• discontinued-product support is defined;
• replacement or repair routes are available during the warranty period.

Without that, the buyer is carrying too much risk.

Alternatives Worth Investigating

For GTR owners who were considering Zestek, KMP produce an R35 GT-R wheel that other people appear to use. https://www.kmpdrivetrain.com/product/nissan-gt-r-r35-my2017/

For Supra owners or CAN-based builds, KMP also produce a universal CAN Bus wheel that may be worth investigating. https://www.kmpdrivetrain.com/product/universal-can-bus-wheel-clubsport/

I have not tested those alternatives myself, so this is not a recommendation. It is simply where I would start looking if I were replacing the Zestek setup.

Final View

Three failures in 15 months on a £1,400 + VAT steering wheel adapter is not acceptable.

The product being discontinued makes the situation worse, not better. If a product is still under warranty, there needs to be a practical remedy. A warranty without available parts, replacement stock, or a clear repair route is of limited value.

Buyer beware.

The post Mk4 Supra Zestek Steering Wheel Adapter Failure: Downshift Paddle Not Working first appeared on BlownByTwins.

The day started, as ever, at my local Shell garage, topping up the tank and driving as slowly to the port as possible, conserving as much as fuel as I could for the few days over there. The Isle of Man Steampacket takes around 2h 45m from Liverpool to Douglas and it’s about what you’d expect, but sailing past the front of my house is a nice touch!

We stayed at the Comis Hotel just outside Douglas, a lovely spot but on the expensive side; it was Manx TT build up week, so they’ve got you…

The first morning as a little misty, but what can you do. You can’t control the weather, so we set off for some exploratory runs on the roads, but it was too misty to really put your foot down until later in the afternoon. So, coffee it was.

In the afternoon it cleared and boy, was it worth the wait! The mountain road was still a bit misty at height, but the other roads, lower done. They. Were. Awesome. The Emtron KV12 Traction Control was .. epic! You can just hear it pulling some timing back in the video below. It was relentless. And the CANTCU controlled ZF8HP70 was superb up and down the gears, it made the pace effortless.

On the last runs of Thursday, up the north west side of the island, the bottom part of the rear wing decided to leave the chat at north of 140mph, and the bottom part decided it still liked me, but it was flapping too much for comfort! Off to the hotel, some hand tools I’d brought and off it came. It left the rear of the looking a little odd!

Fair play to Rival Worx, though. The issue was reported and a fresh wing, under warranty was made and sent out. They stand by their product. It was just one of those things. At least it never caused any other damage, other than to my sphincter.

This brings us on to the main issue with the Isle of Man. Fuel! Weak 97 RON and no E85. Nightmare. And considering the 3.4 at 2.1bar does love to consume fuel, it wasn’t ideal. Especially around 7-8000rpm. The full tank I brought from home lasted a day and a bit. So you’ll either need a standard car, or something that has the secondary maps for 97RON. There’s a resonable supply of fuel on the island, the bigger stations are near Ramsey and Douglas, but you will find them sporadically placed around the island and the price is comparable to home.

I think I’ll be bringing some octane booster with me next time. Given the VP Racing Octanium Unleaded will treat 38 litres of fuel per bottle, and improves by 7 points, I’ll probably end up putting 1.5 bottles in per tank full.

It’ll probably cost £100 extra over the course of a 3-4 day trip, but I don’t get to have 914whp on pump let loose than often! And on an engine build like this, protection is something you absolutely want.

Also, I’d just want to point out the new wheels, with Continental Sport Contact 7 tyres. Not as much outright grip as the A052, but it meant I wasn’t finding religion every time we found a little piece of damp or wet roads. A brilliant all round tyre, and ideal for extended trips where you might encounter some inclement weather.

The final morning was a couple of runs through the Mountains, and going back for the final one as a passenger in Eddie’s 718 Cayman GTS4.0 in Jewish Racing Gold, we found the road was closed. We waited for 35 mins before it was time to go back to the hotel, get our bags and head to the ferry to come home.

Isle of Man, we’ll be seeing you again. Soon. Very soon.

The post Mk4 Supra | Isle of Man 2026 first appeared on BlownByTwins.

The car went back to SRD Tuning to have the engine pulled and the 3.4 built. For those who don’t know what a stroker is, and there’s no shame in that, the standard 2JZ has an 86mm bore and 86mm stroke, giving you 3.0 litres. The stroker crank increases the stroke to 94mm, and combined with an oversized bore you end up at 3.4 litres. More displacement means the engine moves more air per revolution, which means more torque, earlier. It also means a turbo that felt slightly lazy on the 3.0 will spool noticeably quicker on the 3.4. Physics doing the work for you.

The Stroker Bottom End

The bottom end is where the money goes, and it’s where you absolutely cannot cut corners. This is an SRD 3.4 build, built to their spec, and given what they’ve done with my car up to this point, I trust them completely on the component selection. The compression ratio is worth talking about. Higher comp gives you better throttle response, better off-boost driveability, and honestly it just makes the car feel alive at part throttle in a way that a low-comp engine doesn’t. The trade-off is that you need to manage detonation more carefully at the top end under boost, but that’s what the Emtron is for. Dynamic compression is what matters under boost, and between the cam profiles and the VVTi, Mike has that well under control.

The Head: Oversized Valves and Cams

No point building a 3.4 and then choking it with a stock head. The VVTi head has been worked over with oversized valves, which let the engine breathe in proportion to the extra displacement. Think of it this way. You’ve increased the size of the air pump by almost half a litre, so the valves need to flow enough to keep up. Oversized valves increase the curtain area, meaning more air per degree of valve opening. That shows up as mid-range torque, which is exactly where a road car lives.

The cams have been upgraded too. Kelford 202D, long duration, high lift. 272/278, but it still idles at 1000rpm. These are a step up from what a lot of people would run on a street car, but the whole point of this build is that it’s not just a street car. The additional duration and lift open up the top end without killing the bottom, especially with VVTi to pull some timing out of the intake cam at low RPM to keep the idle and off-boost manners civilised. It’s the beauty of the VVTi 2JZ. You get to have your cake and eat it. A fixed cam engine, you’re always compromising. With VVTi, you set the cam timing for the top end and let the ECU sort out everything below it.

The Fuel System

We all know that the 6x 1400cc injectors wouldn’t have cut the mustard, especially where E85 rears it’s little head. And I didn’t want 2600cc injectors killing low speed, low RPM drivability. So I went 12 injectors on a Plazmaman intake manifold, all of them CP1000.

They’re rated at 1000cc at 3 bar, and the car runs 4 bar static with a 1:1 rising rate regulator, so each injector is actually flowing closer to 1155cc. Twelve of those gives you roughly 13,900cc of installed capacity, which is the equivalent of six 2300cc injectors.

Six run as primaries and six as secondaries. The primaries handle idle, around town and low load, and the secondaries stage in when the load arrives, all managed beautifully by the Emtron. That’s the whole point of doing it this way. At idle you’ve only got the minimum pulse width problem of a 1000cc injector rather than a 2300cc one, but at full noise you’ve got the flow of the big ones.

The Bigger Turbo

With the 3.4 stroker built and the head flowing properly, the G40-900 was always going to run out of puff. It’s a fantastic turbo, and the response on the 3.0 was brilliant, but it’s not going to make the numbers we’re after on the bigger engine. So, it’s been swapped for the Pulsar G42-1200. Yeah. A G42. On a Supra. Let that sink in for a second.

The thinking here is simple: the 3.4 will spool a physically larger turbo at roughly the same RPM as the 3.0 spooled the G40-900, because the engine is pumping more exhaust gas per revolution. So you don’t lose the response you had. You just extend the power curve further up the rev range. The G42-1200 has headroom for days. On paper, anyway. The dyno will tell the truth.

Dyno Day

And tell the truth it did. The car went on the SRD dyno and on E85 it put down 1114whp. One thousand, one hundred and fourteen wheel horsepower. From a 2JZ. In a Mk4 Supra. With an 8 speed auto and traction control. Let me just sit with that for a minute.

On pump fuel, it made 914whp, which is still absolutely mental and is what the car will run day to day. The E85 number is the party piece, but the pump figure is the one that matters for real world use. For context, the 3.0 made 548whp. So we’ve doubled the output. The stroker, head work, and G42-1200 have completely transformed this engine.

Both numbers came off the same Dynojet in the same session, uncorrected, so they’re directly comparable. E85 at 2.8 bar gauge, pump at 2.1 bar gauge.

What I can say is that the Emtron KV12 and the 8HP70 together are doing serious work here. The 3.0 at 548whp felt quick through those short ratios, and it felt like a bigger number than it was. So with the 3.4 stroker making over double that, and the Emtron managing the torque curve through the gears via the traction control strategy, this is no longer just a fast car. It’s something else entirely.

• The green line: the old build, 548whp
• The orange line: pump fuel, 914whp
• The red line: E85, 1114whp

But look at the shape. It comes on earlier and lasts longer. Tell me this isn’t the perfect street Supra?!

Putting It Down

With 1114whp on tap, the drivetrain needed to keep up. The OS Giken LSD is now in, along with a 2.93 final drive ratio. The Giken was never a nice-to-have at this power level. It’s the difference between the car putting the power down and the car trying to kill you. The 2.93 ratio lengthens the gearing slightly, which combined with the 8 speed gives you a usable spread across all the ratios without the car trying to spin the rears every time you breathe on it in second.

With the Giken, the new ratio, and the Emtron traction control strategy dialled in for the new power level, this is everything I set out to build. A car for life. One that can cruise to Scotland on a slap! Adventures trip and then rearrange your internal organs on the way home.

SRD Tuning. Heroes. Again.

The post Mk4 Supra: The 3.4 Stroker Build first appeared on BlownByTwins.

As usual, I had the car prepped, with some nice modifications before the trip, and a check over from MK Autos in Blackburn, plus some vinyl sticks from Gary at Stickers At Car Shows. Both always provide fantastic service.

Anyway! On to the night before, as usual we all congregated at the departure hotel in Lancaster. Friends old and new, all sitting and talking about life and the days ahead, whilst Rik, Dom, Imran and Dave all talked about the routes, the refinements, the plans for photos, etc. A couple of gins and many laughs later, we all retired ready to get up and ready for an early departure on Day 1 and the first destination of Kielder. A motorway run up the M6 and then across country, when the convoy starts you know you’re on a trip, my favourite bit!

The car was great, sounded as good as it looked, massive acceleration. Popping the odd little flame for those behind but most of all, surprising a lot of more modern machinery with the grip! 315 rear A052s will also help that, but it’s stuck to the road like a turd to a blanket. These old school JDM cars really are holding their own with the modern tyres and a good alignment on them.

When we arrived at Kielder, it was 3 things: coffee, ice cream and photos. It’s such a picturesque place, and we were so lucky to have the C5 Globemaster doing circuits that it just required patience to get the perfect picture of the Supra on the jetty with the monster flying in the background, kudos to Dave Rutter for getting this perfect shot.

Onwards to Scotland… the roads leading up towards Pitlochry as ever were stunning, amplified by this weather we had, the best of any Scotland trip in recent memory.

The rest of the trip followed this perfect recipe of slow and fast roads, scenery, wonderful hotels and fantastic people. Great food and a beer with like minded people after a day of blasting through the Scottish roads is literally just what the doctor ordered. I’m not going to go into to too much detail on the routes, as that’s specific to slap! but rest assured, it’s every bit as good for each year that passes.

Roll on slap! Scotland in 2026 – and until then, he’s a clip of the best bits.

The post Scotland with slap! Adventures first appeared on BlownByTwins.

I spoke with Peter Kop on Instagram about the supply and fit of the brakes from the Jeep Grand Cherokee SRT8. The reason I decided to go with these was that everything was OEM level quality, the calipers are Brembo, the discs are Lexus. Perfect.

These would be mated up with some Lexus IS-F brake discs, at 360mm front and 345mm rear. But there’s a problem, can you see it yet? Yes, they’re red. I don’t do red. So that needed to be remedied.

I had my friends at Auto Renew Customs in Liverpool powdercoat these for me, and my friends at Stickers at Car Shows provide replica Supra logos to make them look on point.

As you’ll see, the calipers have a notch in them to allow them to clearance a bolt on the hub. This isn’t a concern, and has been done a hundred times. Installation was rounded off with some Motul R660 fluid and stainless steel brake lines.

They look stunningly good on the car. The fitting is a little bit of a bind, but the stopping power and the look they give makes it worth it.

I am having Carbotech UK make me some pads for these, from their XP10 range which will be perfect for the projected 1000bhp the car will have in early 2026. I can’t wait!

LFG!

The post Mk4 Supra – Big Brake Kit (BBK!) first appeared on BlownByTwins.

I sent it off to get painted (along with the powder coating of the brake callipers), and the painter disputes if the legs are actually carbon, despite what’s said on the website. The paint appears to react in a way that is consistent with fibreglass, with small “pinholes” in there. It’s only really noticeable up-close, and the painter has said he will re-paint it if I’m not happy with it (when the car goes in for aerial and rear wiper removal).

The spoiler itself looks pretty good. The high-level is too high, so I moved it down to the medium level.

It’s easy enough to move the wing down to the medium level.

Now that it’s on, I’m relatively happy with how it looks.

Do I like it? Yes, I think I do. Was it worth £850 (on the Black Friday sale), probably not. The delay in the delivery really soured it for me. The lack of communication from the vendor didn’t help. It was me chasing them, not them informing me. I understand that things happen, but a quick message: Black Friday was amazing but it’s created a backlog, we are looking at 10-12 weeks now, if that’s ok? Would have been fine.

Anyway, it’s on and it’s time to research the next mods, which I think will be a Ridox front spoiler and Top Secret rear diffuser to balance it all out a bit. But what I’m most looking forward to is the OS Giken LSD and the new final drive from Neat Gearboxes!

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