Thread: 1990 Grand Prix McLaren Turbo, Looking for some technical info

I have a 1990 Grand prix McLaren turbo LG5 v6 with 3T40-HD automatic trans. Right now it is not drivable due to flat tires and a leaky transmission line.
Anyways, I am trying to find some things out about the vehicle.
I have tried to find this info without much success at all and I do not have a technical book for the car.

1) What is the stock boots levels of the turbo LG5 engine?
2) What boost levels will the ECU kill the injectors and protect the engine?
3) The 4 SPD 4T60-HD transmission, what is the max torque and HP this trans will handle?
4) What is the spline count on the ends of the transmissions where the drive axles plug in?
5) Where can I find a replacement turbo? (What is the ID number for the turbo to be identified with?).
6) What turbo is a good option as far as better response and higher boost capability? Will it bolt right to the existing flange?
7) Where can I find a replacement cross over pipe that the turbo bolts to? (I remember someone used to have one for sale for about 300 dollars and was all welded ready to go with flex sections as well).
8) Is the 4T60-HD transmission electronically controlled by the ECM in any way? (or is it cable controlled off the throttle like the 3T40 trans from GM? I'm assuming the TCC solenoid is the only electronic solenoid as far as shifting/driving is concerned?).

Check out w-body.com or tgpforums.com. Lots more info on those forums too!

Thanks. At least it isn't electronic.

The transmission spline count for the 90 grand prix McLaren automatic says 35.

The car I want to swap this into is a chevy Beretta, the spline count is 35 as well and that is a 4T60E transmission, do you think my Beretta drive axles will plug into the 90 grand prix transmission?

Originally Posted by blueguy

Kuntzie built a 3.1 McLaren car back when, made north of 500~ if I remember right.

But good luck getting ahold of that guy.

Nice. My plan for now is to at least bump the 205 HP and 225 Torque to around 250 HP range and around 275 torque range.
I'm not looking for much, Just enough to give me a bit more of an edge, I do not wish to destroy my transmission. lol
Well, More of an edge than I will be getting; This is going from the 90 grand prix into a 90 chevy Beretta, so I am about 700 lbs lighter than the grand prix.

Originally Posted by Fivefingerdeathpunch

The 4t60e is electronic, it just has a vacuum assist.

Has solenoids for each 1-2, 2-3, 3-4, pressure control and a TCC.

I couldnt tell you how much power and torque it will hold, but 250-300 is a guess. They arent super strong nor are they super weak but if you beat on it alot, it will fail. It'll start to slip and bang gears or break the input shaft.


As far as turbo info and fuel cut off type of stuff, I don't have a clue. I never seen a file from such an old car and not even sure what one could us to tune such a thing. It's so outdated compared to the 97+ computers.

I am pretty sure I have a 4T60-HD not a 4T60E transmission.
I just want to make this clear.

This is a photo of what my transmission looks like:
http://s20.photobucket.com/user/dodg.../4T60.jpg.html
(There is a kick back cable present)

I just want to verify however, will the drive axles from a 4T60E plug into the 4T60-HD transmission?

Originally Posted by Fivefingerdeathpunch

I was answering this part of you question.

It doesnt matter if it was a regular 4T60e or the 4T60e HD, the only difference was the diff and maybe gear ratio on those older ones, both are electronically controlled with a vacuum assist.


I know absolutly nothing about anything older than that or anything in regards to the turbo grand prixs from the early 90's.

The picture you show doesnt look alot like what I call the 4t60e.

They look like this.





Not saying it isnt some sort of 4T60 but I don't really know from that far back.

Okay. I just wanted make sure I understood what you were talking about.

But yes, the one I have is different from the photo you posted, it is the older and more rare non-electronic version. This is probably why I can't seem to find much about it.
I'm just glad I was able to find one of these older 4T60's (no E) that happens to be a heavy duty version.