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.

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.