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Old 05-03-2005, 03:37 PM
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1 2 NV
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Default Brake torque

I am planning on goin to the track to get some baselines before the turbo and I remember reading on here someone saying that if you hit the gas and brake at the same time while in gear the car sort of goes in limp mode. Is this for all z's or just automatics? I have a mt6 and I dont want to try and do one before staging and look like an idiot. If this is in fact the case I guess I'll just have to drop the the clutch a little bit just to get them to spin a warm up just a little bit.
Old 05-03-2005, 10:22 PM
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Aggro_Al
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Originally Posted by 1 2 NV
I am planning on goin to the track to get some baselines before the turbo and I remember reading on here someone saying that if you hit the gas and brake at the same time while in gear the car sort of goes in limp mode. Is this for all z's or just automatics? I have a mt6 and I dont want to try and do one before staging and look like an idiot. If this is in fact the case I guess I'll just have to drop the the clutch a little bit just to get them to spin a warm up just a little bit.
The car needs to have a torque converter to brake-torque. You would use the brakes to hold the car in place while you pre-load the TC to it's stall speed and at the same time cause the transmission to torque multiply. It the AT is equipped with a turbocharger you can pre-spool the turbos (no turbo lag) while doing a brake-torque.

... pro drag-racing cars have heavy-duty auto gearboxes. That's because the brake-torque launch is an automatic specialty. This launch involves keeping the car stationary by flooring the brakes with the left foot, while using the right foot to rev up the engine against the torque converter. In technical terms, this preloads the entire drivetrain with the stress of a launch, allowing the engine to rev closer to its power and torque peaks at the starting line. Brake-torquing is also beneficial for turbocharged engines as it allows boost to build up before the launch, reducing turbo lag. The only problem is that there is a lot of stress on the transmission, and the consequent heat build-up can destroy your automatic gearbox. Unless your car has too much power for the tires to handle, a brake-torque launch usually will not spin the wheels. This is because the automatic transmission absorbs the shock by design, and brake-torquing actually reduces stress on the rest of the drivetrain. Proper brake-torquing will have a catapult effect, immediate torque multiplication gradually traded for velocity until it couples or the next shift occurs.

If your car has power brakes, you could apply the brake-torquing technique even better. At the starting line, shift your auto gearbox into neutral and floor the brake pedal with your left foot. Rev the engine once and quickly get off the throttle. You will feel the brake pedal sink further to the floor. This greatly increases the braking force. Now shift back into gear. You will now be able to rev up the engine even higher against the torque converter.
In the Z, the most common reasons that the car goes into limp mode while doing a brake-torque is because the driver exceeded the stall speed of the TC significantly or the driver held the brake-torque to long. If the driver exceeds the stall speed, the transmission will couple or lock. This would be the AT equivalent of a MT trying to accelerate while in gear and stepping on the brake. The car will attempt to prevent damage by doing various things including cutting the throttle. If the driver holds the brake-torque for a long time, this could cause the transmission to overheat, again, the car will attempt to protect it self by doing various things including cutting the throttle.
Old 05-04-2005, 02:19 AM
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r34 racer
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I'm not aware of any limp mode, but be aware that the ECU will cut throttle response to 20% of its power (or some obscure figure which i have forgotten) while the brake and gas are applied simultaneously. Supposedly this helps with heel-toe downshifting.
Old 05-04-2005, 05:59 AM
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uplz4588
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just pull out the brake fuse and you can standstill burnout... if thast what you mean by brake torque.
Old 05-04-2005, 07:29 AM
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Aggro_Al
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Originally Posted by r34 racer
I'm not aware of any limp mode, but be aware that the ECU will cut throttle response to 20% of its power (or some obscure figure which i have forgotten) while the brake and gas are applied simultaneously. Supposedly this helps with heel-toe downshifting.
Hmm? To do heel-toe downshifting in an MT you would need to engage the clutch at the same time so that the throttle can be blipped. Why would the ECU cut the throttle unless you released the clutch too soon? Not trying to flame, just curious.

Heel-toe downshifting isn't necessary on most modern ATs because they have computer-controlled clutches and/or a torque converter. The Z 5AT has both.
Old 05-21-2005, 12:21 PM
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Originally Posted by 1 2 NV
I am planning on goin to the track to get some baselines before the turbo and I remember reading on here someone saying that if you hit the gas and brake at the same time while in gear the car sort of goes in limp mode. Is this for all z's or just automatics? I have a mt6 and I dont want to try and do one before staging and look like an idiot. If this is in fact the case I guess I'll just have to drop the the clutch a little bit just to get them to spin a warm up just a little bit.
the ecu cuts power to by 30% actually when both pedals are pressed. so you will actually lose power on take offs when you do that. you can pull the fuse to trick the ecu into not being able to sense that both pedals are pressed. i sell a kit that hooks into the fuse panel and routes it to a switch for easy on/off controll. $35 shipped. pm me if your interested.
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