Pulling trac fuse in an auto?

As some of you know (and I just realized thanks to Mohd) Supra AUTO's will experiance drop in boost during shifts.
Normally everyone with a 6sp knows that during shifts (unless you do it really well) you will experiance a drop in boost during the shift itself. On an auto it depends on wether or not you have TRAC computer still in the car and enabled.
As an experiment I ran 1.3kg of boost with TRAC on and enabled and during each shift I would see a drop in boost. The car would also feel like a 6sp during shifts ;-).... slight spin when the gear engaged.
Here is a picture of what that looks like on an AVC-R






You can ignore the not-so-smooth curve up to the shift as I was passing someone.
Basically its a 2nd->3rd shift done by the transmision itself without help from the driver [;-)] and during the shift a major boost drop is very visible.

Removing the TRAC fuse or pulling the TRAC computer makes the auto hold boost during shift. I will let the more technical members explain how TRAC butterfly works if anyone is interested.

Here is what it looks like without TRAC in the car (or with a fuse pulled)



Suffice it to day that having TRAC is good for you in the rain and bad for you when you don't want to loose boost.

What effect it has on the transmission.... I am sure its not helping prolong its life [;-)]

I had my 98 auto BPU'ed running 1.3kg on daily basis for at least 40k miles so far without any issues just for reference.

Cheers,
-Kapi
98 TT auto BPU+

kapi said:

What effect it has on the transmission.... I am sure its not helping prolong its life [;-)]

I had my 98 auto BPU'ed running 1.3kg on daily basis for at least 40k miles so far without any issues just for reference.

Cheers,
-Kapi
98 TT auto BPU+

Click to expand...

Toyota built the traction control system into the transmission's operation for a reason. It just can't handle the power of a WOT shift. And when you start turning up the power, you'll start to blow the tranny.

You're are correct about loosing some boost during shifts w/ the trac fuse in. On a normal auto tranny or when running w/ out trac on the Supra, boost will actually spike during shifts. This may sound like a cool idea, but not really the best. Boost is spiking putting more power through the tranny, and more wear and tear. Besides the fact that on my stock tranny w/ out the trac in, boost would spike from 1.2bar to 1.4 and this is not that good of an idea on stock turbo and especially on pump gas.

You've been lucky to have your tranny last for 40k miles if you've had no trac fuse in. But as a rule of thumb you should leave it in. If you continue to drive on a daily basis w/ out the trac fuse, you'll eventually (hopefully later than sooner) be posting asking why your car bounces off the rev limiter between shifts. This will mean that the stock clutches and line pressure cannot hold the power anymore and are slipping.

A tranny cooler is an extremely good idea, and so it changing your tranny fluid every 10-15k miles instead of every 30k miles. And having the valve body upgraded will definitely prolong the life of your tranny, but you're still dealing with the stock clutch material. Even with Level 10's tweaking of the valve body and upgrading of the clutches (so they claim) the tranny can't handle the power. (Mine lasted a whole 9 months of street driving mostly at 1bar, this is worse than stock) If you want to run without the trac system, you ought to do it the right way and build the whole tranny.

JZ1,

Very well said.

suprat10,

The SP tranny can handle the WOT shifts that occur w/ out the trac system.

2bad4U,

It should be ok to turn off/cut out the trac fuse when the car is on as long as you are at a complete stop. The only thing I can think of going wrong is that you kill it while the Sub-throttle plate is engaged and then you have it blocking airflow. But I can't be certain that it won't mess something up. And I don't think the extra wear on your tranny will outweigh the slight pick-up in times.

supra935,

You're very lucky, my Level 10 lasted 9 months of normal street driving at mostly 1bar and ocassionally 1.2bar. The Pat wanted $1500 plus shipping to fix it, and he propbably would've charged me for the extra $500 in blown up parts that I had. There are many others out there that have had Level 10 trannies blow up on them, some lasted 3 days, and some lasted a few years.

Do yourself a favor and change your tranny fluid very often (at least every other oil change) this will help prolong your tranny's life. And if you haven't already, go out and find yourself the biggest tranny cooler you can find.