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1990 Indy turbo

Posted: Wed May 10, 2017 8:33 pm
by Chevyrider215
I have a nice Indy edition with a 3.1 MFI turbo out of a grand prix McLaren was tuned by the previous owner and it has a rebuilt 4spd auto transmission that supposed to have like a shift kit where you have to let out for it to shift from 3-4 gear well I decided to take it for a test run when a new Chrysler 200c decided he wanted to try me so we were already at a roll and when I punched it the car was pulling hard until I reached about 120mph and it pegged out like it was hitting the rev limiter ..I'm not sure if the car was tuned without adjusting or removing the limiter anybody know how these cars work?

Re: 1990 Indy turbo

Posted: Thu May 11, 2017 9:41 am
by ifixalot
There is probably a rev limiter. I don't know how to bypass it.
FYI, just to make you aware, 120 mph on the street is extremely reckless.
In our area, there was a family of three killed by some chump doing over 100 mph on the street. ... 00mph.html

I suggest you think long and hard about how you'd feel if you killed somebody with that speed.
Go to a drag strip and race.

Re: 1990 Indy turbo

Posted: Thu May 11, 2017 9:51 am
by themixer

I assume the car is this one that sold

Re: 1990 Indy turbo

Posted: Thu May 11, 2017 11:58 am
by Chevyrider215
Yes I'm aware of endangering others while speeding that's why there were no other cars around and it was a open freeway still i had no business of going that fast but there also was no other vehicles that were in our path just us two going at it

Re: 1990 Indy turbo

Posted: Mon May 15, 2017 12:58 pm
by 3X00-Modified
Never heard of that type of shift kit... Perhaps it's just a limitation of the mechanical 4 speed trans vs the electronic version... Besides that though... I know what can be done to these transmissions and I can assure you that wanting the trans to shift into 4th gear while at WOT will result in 4th gear burning up. That clutch pack consists of two fiber discs and 3 steels, it is in no way designed to take that abuse and honestly can't be upgraded to do so. A 4th gear WOT pull is not recommended. You were probably hitting a rev limiter in the ECU and that was stopping you at that speed, Do you happen to know what RPM you were at?

Re: 1990 Indy turbo

Posted: Tue May 30, 2017 7:57 pm
by JeffD
GM preprogrammed the engine computer to interrupt fuel when a certain speed was reached (it has to do with the speed ratings on the original tires). My '88 would cut fuel at 120mph. The first time it did it, I freaked out, the sudden deceleration made me think something came unglued in the engine! I kicked the clutch and it stalled, I let it coast to a stop before restarting. It fired right up.

Are you sure you have a four-speed auto? If you've got the three speed that last shift could be the torque converter engaging.

Sent from my MotoG3 using Tapatalk

Re: 1990 Indy turbo

Posted: Wed May 31, 2017 8:58 am
by 3X00-Modified
This is a custom built car running a 3.1 Intercooled turbo from a GTP including the mechanical 4-speed automatic trans, aka the TH440

Re: 1990 Indy turbo

Posted: Mon Jul 03, 2017 4:40 pm
by GT_Indy
I just now noticed the thread, sorry for the delay.

Yah, When I paid AAMCO to rebuild the transmission they told me that there was a shift kit put in where the driver needed to let off the gas and re-apply to allow it to shift to 4th gear from 3rd gear to protect it from burning up under WOT throttle, but part throttle it shifted 1-2-3-4-TCC normally.
When I did the EEPROM tune I had set the speed limiter to 225 mph (max value it could allow).
Personally I never went over 90 mph with the car so I don't know the max speed it is capable of.

Here is a link to a write up for that transmission that is in the vehicle:

I gave the Vin from the 90 Grand Prix that was parted with the service books I gave with the car, I don't know if that vin can be used to find the exact gear ratios that vehicle came with.

The 3T40's had this:
1st - 2.84
2nd - 1.6
3rd - 1.0
Final Drive Ratio - 3.18

The link says the 4T60 in the vehicle has this:
It also says the 440-T4 (4T60) was available with the following differential ratios: 2.84, 3.06, and 3.33.

Link to wikipedia for sme information:
The Turbo LG5 engines were fitted with the 4T60-HD's which had stronger final drive hardware.