Then I logged it properly. The logs showed that the tyre produced its best acceleration at less slip than some of my more permissive modes allowed, the speed offsets could drive the final target below zero, and the integral term was storing positive torque while the car was below target. When wheelspin arrived, part of the PID was briefly helping it.

This is the latest iteration: what changed, what the evidence actually supports, and what still needs a warm, dry road before I call it finished.

The starting point

Status: Verified – Rear tyres are 295/30/19 Continental SportContact 7s.

The strategy has always had two halves. Feedforward predicts the engine torque the tyre should accept. Closed loop PID then corrects whatever the prediction could not know about: temperature, damp patches, surface changes, load transfer and bumps.

The torque model is normalised to third gear. The traction strategy itself is not normalised until the final gear scaler is applied. That distinction matters because a torque value in the base table is not the engine torque the car will necessarily receive in second, fourth or fifth.

The tyre peak moved the targets

Status: Working conclusion

The useful result from the earlier dry data was a tractive force peak around 9,500 to 9,800 N at roughly 5 to 6 percent slip. Once slip moved into the 6 to 8 percent band, median tractive force fell to about 8,860 N. More wheelspin felt more dramatic, but it accelerated the car less.

That immediately made two settings look wrong. Mode 7 allowed 7.9 percent straight line slip and Mode 9 allowed 12 percent. Both sat beyond the measured force peak. They were permissive, but they were not the fastest settings.

The later road test complicated the picture. It was cooler and the road was not completely dry. Maximum logged tractive force was about 7,982 N rather than 9,500 N. The road rose by only about 0.17 percent over the measured section, worth roughly 30 N on a 1,750 kg car, so gradient could not explain the difference. Tyre and road condition could.

That means 9,500 N remains a dry baseline, not a universal grip limit. The system still needs slip feedback because no fixed torque table can know whether the tyre is warm, cold, dry or sitting on a damp seam.

Rebuilding the rotary modes

Status Calibration loaded for validation

The rotary still selects the character of the car, but the straight line targets now have a cleaner progression. Mode 3 remains the chilled setting. Mode 4 is the normal fast road setting. Mode 5 is for a known dry road on warm tyres. Mode 6 allows movement, but no longer asks the SC7 to live well beyond its measured force peak.

The lateral G shapes were rebuilt at the same time. Both sides are now symmetrical because there was no evidence supporting different left and right targets. Every active road mode tapers as lateral acceleration increases, because the tyre has less longitudinal capacity available while it is also producing cornering force.

The speed offset was doing too much

Status: Calibration loaded for validation

The final target is the lateral G table plus a speed offset. The old high speed offsets were large enough to make the combined target negative in the conservative modes. Unless that is correcting a measured wheel speed bias, a negative slip target has no useful meaning.

The revised table keeps the low speed launch allowance, but reduces the 25 km/h addition from nine percentage points to five. The target now blends down towards the normal table by 45 km/h instead of falling off a cliff. Above 180 km/h the negative offsets remain, but they are smaller and cannot erase the underlying target.

That gives the same rotary a consistent meaning at every speed. Mode 3 remains conservative rather than becoming impossible at high speed, and Mode 7 remains the quickest dry road target rather than turning into an arbitrary number once the car passes 180 km/h.

A feedforward table built around tractive force

Status Current baseline

The largest architectural change is the main feedforward surface. Instead of treating slip error as the only description of available grip, the new table is indexed by modelled tractive force and engine torque before reductions.

The surface rises towards 9,500 N, then deliberately falls away. At a 950 Nm unrestricted torque input, the table returns 594.9 Nm at 8,000 N, 652.7 Nm at 9,500 N and 597.1 Nm at 10,500 N.

Apply the fourth gear normalisation factor of 1.263 and those become approximately 751, 825 and 754 Nm at the engine. The peak is therefore almost exactly where the warm, dry SC7 data said it should be. Above the peak, the table asks for less torque because the tyre has already moved onto the wrong side of its force curve.

This is still a model. Emtron tractive force is largely derived from engine torque and gearing; it is not a strain gauge measuring the contact patch. The table provides a gear aware first estimate. Slip feedback remains the part that discovers the road is wet.

The integrator was adding torque

Status: Verified defect

The most important log finding was not a lack of negative integral authority. It was positive windup.

With slip below target, the original controller allowed the integral output to climb to its positive 50 Nm clamp. One run held it there for about 1.3 seconds. Another retained the full 50 Nm across approximately 2.75 seconds. The tyre was not slipping too much, so the controller stored permission to add torque.

When overslip arrived, the proportional and derivative terms reacted immediately, but the integral term had to unwind before it could help. At the worst point in one event the contributions were minus 7.6 Nm proportional, plus 37.6 Nm integral and minus 0.9 Nm derivative. The combined PID contribution was still plus 29.1 Nm while the tyre was already beyond target.

The controller remained stable because the feedforward model, throttle reduction and ignition retard were doing the real work. That does not make the integral behaviour acceptable. A stable result can still contain two control terms fighting each other.

The fix was removing positive authority

Status: Changed awaiting full dry validation

The positive integral clamp is now zero. The negative clamp remains minus 50 Nm.

Below target slip, the integral term now sits at zero. Once the tyre exceeds target it can accumulate negative correction, up to 50 Nm. There is no positive value left to unwind and no stored torque waiting to oppose the first intervention.

I initially considered extending the negative clamp to minus 75 Nm. The logs killed that idea. In the later full throttle events the negative integrator reached only minus 4.3 Nm in one run and zero in the other. More negative authority would have solved a problem that was not happening while increasing the risk of a torque hole after the tyre recovered.

The proportional, integral gain and derivative tables therefore stay unchanged for the next test. Changing several control terms at once would make the result impossible to attribute. The positive clamp was the proven defect, so that is the change being isolated.

What the road logs now say

Status Verified for the logged conditions

Both runs used the conservative Mode 3 target. Neither needed ignition or fuel cuts. The car controlled the tyre with modest timing reduction and without the controller cycling torque up and down.

The lower 7,982 N tractive force result from the cooler, imperfectly dry run should not be used to rewrite the dry table. It is evidence that the available grip changed. That is exactly why the feedforward and feedback halves both exist.

The same session produced a roughly 4.8 second 100 to 200 km/h run without full boost at 100 km/h. The performance matters, but the cleaner result is the behaviour: a 914 whp pump fuel car remained controlled on a cool road without cuts or abrupt throttle closure.

Power mode and traction mode are separate decisions

Status: Verified

The torque request rotary decides how much engine performance is available. The traction rotary decides how much of that performance the tyre may use. Treating them as one setting hides useful control.

The high torque modes already allow enough demand to exceed the rear tyre in second and third, while effectively releasing full engine output from fourth upwards. Increasing those torque tables would not make the car faster. It would only give the traction strategy a larger error to remove.

For a dry road the useful combination is a high torque request with Mode 5 or Mode 6 traction control. Mode 3 is deliberately conservative. Mode 7 is now a permissive track setting rather than a 12 percent wheelspin setting dressed up as performance.

The current configuration (Emtron specific)

What still needs proving

The next valid test is on the same dry road, in both directions, with warm tyres. Running in both directions removes most of the gradient and steady wind error. Mode 4 should be tested first, followed by Mode 5, with full pedal held through the shift long enough to see the integrator unwind and torque recover.

The stop condition is simple. If slip rises beyond about 6.5 percent and tractive force does not increase, the tyre has crossed the peak. If force continues to rise at 5.5 percent slip, Mode 6 is doing its job. If the controller oscillates or leaves a torque hole after intervention, the PID still needs work.

Until that test is complete, the new force peak and the revised permissive modes remain evidence based working settings rather than finished calibration.

The lesson from this iteration

The first version was designed to prevent wheelspin. This version is being calibrated to maximise acceleration without making the car unpleasant.

That distinction changed the questions. How much slip is allowed is less useful than where the tyre produces maximum force. A larger integral clamp is less useful than checking whether the integrator is acting in the correct direction. More available engine torque is irrelevant when the tyre is already the limit.

The car already had enough power. The latest changes are about making the control system stop wasting it, whether that waste comes from excessive wheelspin, an over-conservative target or two parts of the PID fighting each other.

That is the point of logging it properly. The calibration stops being a table that looks sensible and becomes a system that can explain what the car actually did.

Huge thanks to Adrian at Emtron Australia for the pointers in this. It’s been invaluable.

The post What the Logs Changed in My Supra Traction Control first appeared on BlownByTwins.

This is how I worked outwards from the symptom until the log told me where to look, and what the arithmetic said once I got there.

Ruling things out

Status: Verified

I expanded the log window out and walked the closed loop items one at a time. First question: was idle control intervening during the downshift? It was not. Verified and set aside.

The next thing I noticed was that air mass was going erratic, and that is worth being precise about, because the air mass model on this car is a blend. Below 100 kPa it runs the throttle mass flow model exclusively and blends towards speed density above that. In the region where this fault appears the air mass estimate is therefore a function of throttle effective area and pressure ratio and nothing else. No speed density term diluting it, no trapped mass term in the estimate.

So erratic air mass in that region means the blade, or the area characterisation, or both. It cannot mean much else.

Pedal throttle demand translation was smooth through the whole event. The driver demand table was not doing this. That left the DBW loop, and the DBW PID was the gold seam.

What the loop was doing

Status: Verified

Three things stand out.

Proportional output is saturating at minus 100 percent repeatedly, and topping out near plus 63. That asymmetry is not the axis autoscaling being unhelpful. It is the loop reaching its closing clamp over and over while never reaching the opening one.

Integral output is sitting around plus 24 percent and climbing slowly across the window. An integrator that keeps accumulating while the proportional term is pinned at its clamp is not doing the job an integrator is for.

The motor command is swinging roughly minus 65 to plus 100 percent while the measured blade position only moves a few percent either side of 15. The blade is inertially filtered. It physically cannot follow a command oscillating at that rate, so the engine never sees the full excursion.

That last point is the one that connects back to the shift. The engine does not see it, but the model does. Torque estimate comes from air mass, air mass in this region comes from the throttle mass flow model, and that model reads blade position directly. Every percent of blade wobble goes into the torque estimate whether or not the engine produced any of it.

The gearbox was reacting to torque noise that did not exist at the crankshaft.

The arithmetic

Status: Verified

This is where the log stops being suggestive and starts being conclusive. At the cursor, 38.138s in the screenshot above:

• Servo Position Main: 3.7 percent
• Proportional output: 0.9 percent
• Integral output: 24.3 percent
• Derivative output: 0.0 percent
• Motor command: 6.2 percent

My feed-forward table runs minus 30 at 0 percent and minus 15 at 5 percent. Interpolated linearly, feed-forward at 3.7 percent is minus 18.9.

Two things fall out of a match that close. Motor command is the summed controller output rather than a measured position, and feed-forward interpolates linearly between breakpoints.

But the finding is the third thing. At a near steady 3.7 percent blade position, the integral had wound to plus 24.3 for no purpose other than to cancel a feed-forward of minus 18.9.

The feed-forward in the 0 to 5 percent band is asking for roughly 25 points of closing duty that the throttle body does not need. The integral is spending its entire authority undoing it. That is a large stored state sitting permanently in the loop, and every time the proportional term saturates and the target moves, that state has to unwind before anything else can settle.

It is a far better explanation for a sustained oscillation than any single gain cell.

The feed-forward step, and what it actually is

Status: Provisional

There is a 25 point change in motor duty for a 1 percent movement in target between 5 and 6 percent, and the log crosses that region immediately before one of the instabilities. My first instinct was that this was simply wrong. It is not, and this is the part most likely to be copied badly, so it is worth saying plainly.

The return spring on a DBW body pulls the blade towards its limp home position from both directions. Below limp home you need negative duty to hold the blade down against the spring. Above it you need positive duty to hold it open. A feed-forward table that changes sign between two cells is not a tuning error. It is the table telling you where limp home sits.

Delete the step and you have not removed the discontinuity. You have removed the compensation for it, and handed the spring preload to the integrator.

The real problems are different. First, the magnitude of the low band values, which the arithmetic above says are too negative. Second, a 25 point change interpolated across 1 percent of travel behaves like a gain of 25 through a region the blade is oscillating in.

The proportional gain table

Status: Provisional

The low position P gains are aggressive, and lopsided towards the negative error side.

Reading negative error as blade above target, the closing correction gets close to twice the gain available for an equivalent opening error, at every row.

The spring makes this more interesting than a simple symmetry argument, because the asymmetry it creates flips across limp home. Above limp home the spring already assists closing, so the loop needs more authority to open and less to close. Below limp home it reverses.

A table that favours the closing side at every row is therefore directionally right in the 5 percent row and wrong in the 15 and 25 percent rows. The blade sits at 15 to 17 percent through this event.

One caveat that anyone copying this needs to take seriously. The whole reading above depends on the error channel being target minus actual. If your ECU signs it the other way, the argument inverts and so does the revision. Confirm it on your own log before you touch a cell: find a step where the blade visibly lags a rising target, and read the sign.

What I have not proved yet

I changed two tables at once. Until they are separated, no outcome can be attributed to either.

I have not measured the true limp home position. The right way is to unpower the driver and read the TPS, then check whether the feed-forward breakpoints actually straddle it. If limp home sits at 6.5 percent rather than between 5 and 6, the compensation is being applied in the wrong place, and that alone would explain the instability without a single gain change.

I have not confirmed the error sign convention from a step.

And I left the 0 and 5 percent feed-forward cells alone, which are the two cells the arithmetic actually points at.

I’m not declaring this as “fixed” yet. However, the gear change is smoother, particularly the upshift. The lower speed acceleration is cleaner and everything just feels much more refined. Always remember the first few percent of opening on a throttle blade are extremely non-linear, and even more so on a 82mm throttle body.

The test that closes it

With the loop stable, park the blade at steady positions across 0 to 25 percent, in 2 percent steps through the 0 to 8 percent band, and log feed-forward and integral at each point.

Wherever the integral is non-zero at steady state, the feed-forward is wrong by exactly that amount. That lets the whole low band feed-forward table be built by subtraction rather than by iteration. The position at which feed-forward crosses zero and the integral stays at zero is the true limp home. Any step within the sweep settles the sign convention.

Run it on the same road and the same coast down and you also get a genuinely matched before and after, rather than two logs taken a week apart under different load.

The principle

The data is not transferable, but the principle is.

A feed-forward table and an integrator are solving the same problem from opposite ends. If the integrator is carrying a large standing value at a steady operating point, the feed-forward is wrong by that amount, and you can read the correction straight off the log instead of iterating towards it.

The throttle area table that the whole torque model sits on is covered in Throttle Body Effective Flow Area, and the same feed-forward versus PID argument applied to traction control is in Traction Control on 1,114 whp. Full specification is on the Supra project page.

If you run a DBW loop and have taken a different view on any of this, particularly the limp home reasoning or the gain asymmetry, I would like to hear it.

The post Erratic Shifts and Idle Overfuelling on the 2JZ: Finding a DBW Feed-Forward Fault first appeared on BlownByTwins.

Most discussion of traction control stops at “it cuts power when the wheels spin”. That describes about a third of what is actually happening, and it is the least interesting third. The system on this car has a predictive half that tries to never need the reactive half, and the whole design is aimed at keeping the reactive half quiet.

This is how it is set up, and why. Every table is reproduced in full.

Configuration

Status: Verified

• Emtron KV12, torque based traction control
• 3.4 litre 2JZ-GTE VVTi, 1,114 whp on E85, torque limited to 880 lb ft
• ZF 8HP70, 2.93 final drive, OS Giken LSD
• Continental SportContact 7, 265/30/19 front and 295/30/19 rear
• Four individual wheel speeds, three axis internal accelerometer
• Eight position rotary on the steering wheel, over CAN

Everything below is my own work. The base calibration on this car came from SRD Tuning, but the traction control strategy is mine start to finish, which is the only reason I can show you the tables.

The predictive half: torque feedforward

The core of the system is a table that answers one question: at what engine torque does this car lose traction?

It is indexed on engine torque with no reduction applied, against slip target error. The ECU looks up that number and feeds it forward as the torque target before any measurement of actual slip has influenced anything.

That is the whole idea of feedforward. If the model is right, the engine never makes more torque than the tyres can take, the slip never happens, and the closed loop has nothing to correct.

Look at the first two columns before anything else. At 50 Nm of engine torque the table returns 50, and at 150 it returns 150. Below about 150 Nm it is a pass through: the feedforward is not limiting anything, because at those loads there is nothing to limit.

And this is where the normalisation matters

Read along the zero slip error row and the values climb: 245.3, 340.5, 430.9, 478.9, 527.0, 575.0. And then they stop. Flat at 575 Nm from 750 Nm of engine torque all the way to 1,250.

That plateau is deliberate and it is the single most important thing in the setup.

Extend the slope before the plateau and an unclamped table would be asking for roughly 815 Nm at the top of the range. The engine makes 1,193 Nm. So without the clamp, the feedforward would be handing the PID a target the tyres cannot deliver, and the PID would spend its entire life trying to close a gap that physics will not close.

A saturated PID is not a controller. It is an actuator held wide open. You lose all the proportionality that makes traction control feel like assistance rather than interference.

Clamping the feedforward at something the tyres can actually deliver means the PID always has authority in reserve. That is what “normalised” means here, and it is why the system feels like it is helping rather than fighting.

Normalised against third

The feedforward table is written for third gear. Everything else is scaled off it by two correction tables.

Correction Table 1 is indexed on gear against rate of change of engine speed. In first at low dRPM the correction is zero. By eighth at 4,000 dRPM it is minus 32 percent.

Which makes sense once you think about what dRPM means in each gear. Engine speed rising at 4,000 rpm per second in first is normal acceleration. The same rate in eighth means the driven wheels are going somewhere the car is not. The correction is reading the rate of change as evidence of impending slip, and pulling the target down before the slip calculation has caught up.

Correction Table 2 does the same job against slip target error directly, from minus 40 percent at large negative error up to plus 10 at zero. That positive 10 at zero error is worth noticing: when the car is exactly on target, the feedforward is allowed to ask for slightly more than the base table says.

The slip target, and what the rotary actually does

Status: Verified

Here is the part I had not seen anyone else do.

The target slip table is indexed on lateral G, from minus 1.5 to plus 1.5, against the rotary position from the steering wheel.

Almost every row is a dome. Maximum permitted slip in a straight line, tapering symmetrically as lateral load builds in either direction. At the loosest setting the car allows 28 percent slip straight ahead, falling to 25 at 1.5 G. At the tightest, 2 percent straight ahead and 1 percent once the car is properly loaded up.

Setting 1 is the exception, and I would rather point at it than pretend it fits. It permits 2 percent straight ahead, rises to 3 percent at around 0.75 G in either direction, and comes back to 2.5 at full lateral load. It is the only row in the table that allows more slip while cornering than it does in a straight line.

So the rotary is not a gain switch and it is not an on/off. It selects how much slip you are allowed as a function of how hard you are cornering, and the system tightens automatically as lateral load increases without the driver doing anything.

And then speed offsets all of it

Lateral G is not the only input to the slip target. A second table offsets it by road speed, and it does a lot of work at both ends.

Below 25 kph every setting adds nine percentage points of slip, and the loosest adds twenty five. That is the launch allowance. You cannot get a car like this moving from rest on a target of 2 percent, and without that offset the system would strangle it off the line.

Between 45 and 160 kph the offset is zero and the lateral G table stands on its own. Above 180 it goes negative, and by 330 kph it is pulling back between 2 and 9.4 points depending on the setting.

Which is the right way round. Wheel slip at 40 kph costs you a bit of time. Wheel slip at 300 kph costs you rather more than that.

The reactive half: a deliberately soft PID

Status: Verified

When the feedforward is not enough, the PID takes over. And the gains are the opposite shape to what most people would write. All three share exactly the same breakpoints, so they go in one table.

Proportional gain at zero slip error is 0.20. At minus 25 percent error it is 3.00. Derivative runs the same way, 0.10 at zero, and it saturates at 3.00 from minus 20 onwards.

Both are smallest near target and largest far from it.

That is a controller designed to be felt as little as possible. Around the target, where you spend almost all of your time, the loop barely reacts and the feedforward carries the car. Only when things run properly away does it bite hard.

Tune it the conventional way round, with high gain near target for tight regulation, and you get a car that nibbles at the throttle constantly and feels like it is arguing with you.

Integral is almost switched off, on purpose

Look at the integral row against the other two. Peak gain is 0.020, near target. At minus 25 it is zero.

Zeroing the integral term exactly where the error is worst is anti windup by design. When the car is genuinely out of shape, the integrator stops accumulating instead of building up a correction you then have to unwind on the way out. An integrator that has wound up during a slide gives you a second event when it releases, and the second one is usually the one that catches people out.

The rest of the PID setup backs that up:

• Integral control rate: 200 Hz
• Integral positive clamp: 50.0 Nm
• Integral negative clamp: -50.0 Nm
• Minimum torque clamp: 50.0 Nm
• Slip target filter: 4

Fifty Nm either side is a narrow band on an engine making 1,193. The integrator is there to trim, not to intervene.

And the PID does not always run

Below 300 Nm of driver demand it is zero across the whole row. The closed loop simply does not run.

Above that it opens up as a staircase. At 300 Nm the loop only runs once slip error is worse than minus 3 percent. Every additional 100 Nm of driver demand brings one more column into play, until at 1,000 Nm it is active everywhere except the far positive corner.

So the amount of authority the closed loop has is itself a function of how much the driver is asking for. At low demand, feedforward handles everything alone, which means the PID cannot introduce noise into normal driving, because at normal driving loads it is not switched on.

What it is allowed to do about it

Emtron gives you three actuators for torque reduction, in a priority order. Mine reads throttle area, then ignition retard clamped at 11 degrees, then OFF.

Cutting is disabled. On a car making 1,114 whp, the harshest tool in the box is not in the box.

The throttle area minimum clamp bottoms out at 10 percent, so it never closes the throttle fully either. Torque reduction happens by moving the plate and pulling timing, and nothing else.

That is a road car decision. Fuel or ignition cutting is fast and effective and it feels like being kicked. On a car that has to be pleasant on a motorway and predictable in the wet, an intervention that arrives as a smooth reduction rather than a hammer blow is worth more than the extra tenth of response.

Does it work?

One number from a road log, second gear, full throttle:

Torque reduction by retard: 8.1 percent.

Eight percent, in retard, on the second priority, with cutting unavailable and throttle intervention having already done its part. That is the system working gently in the conditions where a badly normalised setup would be reaching for everything it had.

It is one data point from one log, so treat it as an illustration rather than proof. But it is the shape of result the whole design is aimed at.

The principle, if you take nothing else

A PID is not there to make your feedforward work. It is there to handle what the feedforward could not have known about: a damp patch, a change in surface, a mid corner bump.

If your feedforward target is unrealistic, the PID spends its authority correcting your model instead of correcting the road. It saturates, it escalates through the actuator list, and the car feels like it is fighting you.

Normalise the target to something the tyres can actually deliver, gate the loop so it only runs when it is needed, keep the gains soft near target, and the reactive half stays quiet almost all the time.

Which is the point. The best traction control is the one you do not notice.

One thing to be clear about

Every number above is specific to this car: this power, these tyres, this gearbox, this weight distribution. The data is not transferable, but the principle is.

I have published the tables in full because seeing how something is structured teaches you far more than reading a description of it. Copy the structure. Do not copy the values.

None of this works without trustworthy wheel speeds, which on a staggered setup is less automatic than it sounds. That is covered in Staggered Tyres and Traction Control. The throttle area table that the whole torque model sits on is covered in Throttle Body Effective Flow Area. Full specification is on the Supra project page.

If you run torque based traction control and have taken a different view on any of this, particularly the gain shape, the setting 1 anomaly or disabling cut, I would like to hear it. This is the part of the calibration I have changed my mind about most.

The post Traction Control on 1,114 whp: Feedforward, PID, and Why It Never Cuts 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!

The post Mk4 Supra – Rival Worx TRD Style spoiler first appeared on BlownByTwins.

The only real issue was the extended traffic jam and a solid hour of nose to tail traffic which saw the gearbox temperatures get close to the maximum.

On arriving at the JDM North pitch, we were placed in a pretty disappointing place, right at the back on row 3, and the end of the pitch. So we decided to make the most of it and reverse in to the pitch so at least we’d be pointing out to the passing crowd and I could get the Supra bonnet open to show off the Pulsar G40-900 and the SRD workmanship in the engine bay.

Comments were very complementary! Thank you to everyone I spoke to!

Mooching around the show was a real mix, some fantastic builds, with boundless time, energy and money put into them – right down to your ghost MOT examples, and there were a few…

Was great to meet up with Mark from Pulsar Turbos, and thank him for the endless support, and also with some old fellow R35 owners who were parked up quite close. It’s always great to see great people.

The drive home… TC set to 30% and power turned up to the max. Some controlled exits of roundabouts, power being deployed seamlessly. It’s just a joy. Then the cruise control on, via the M1 north to the M6, and settled in with some Chris Harris podcasts.

This car is special – and it’s only getting better.

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