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.

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

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