Need Help with Engine Swap

[communityracingchallenge]

I have a 1990 Pontiac Grand Prix which I Circle Track Race. It has the Gen II, 3.1L V-6 motor.



We have been getting beat pretty regularly over the last 2 years, but it was a good safe beginners car and I didn't mind so much.

We put together a 2nd Grand Prix, which had the 3100 MPI motor.. and with the help of folks here, we were able to mod that motor enough to make it a 1st place car !



But the driver of that car has really matured and we are ready for two fast cars.. not to mention.. the competition has gotten a lot faster. 3.5L Dodge Intrepids, Ford Taurus SHOs, Chevy Lumina GTZs..

So the question becomes.. what is the optimal thing I can do to make this 1990 Pontiac Grand Prix scoot !

Switch to a 3400 ? a 3500 ?? a 3800 ?? maybe swap in a 3.9L ???

What do you guys think.. off from a 90 W-Body Grand Prix what is the best bang for the buck we can make.

Remember.. Circle Track.. not Drag racing. No Turbos, No Super Chargers.

[3100 MPFI]

I would do the 3500 non VVT engine (can't remember exactly what car it was in), but a swap is going to be your best bet. The 3500 would give you more displacment, and right out of the box, it has some added benifits of the newer style heads, and intake manifolds.

You do NOT want to use the 3800 buick engine. For racing, you need light weight, and that 3800 is a good deal heavier.

[communityracingchallenge]

Is this the Olds 3500 nicknamed "shortstar" used in the Intrigue and the Aurora ?

[3100 MPFI]

No. The 3.5 Shortstar was basically an Aurora 4.0 with 2 cylinders cut off. It is a 90 degree engine.

The 3500 is basically a 3400 with a different intake manifold, and larger displacment. They use it in the Malibu, and G6, but I am not sure what cars get the VVT version, and which ones are NON-VVT.

If I was going to go with a newer DOHC engine, then I would use the new 3.6 that the caddy, and buick's get. I think they are going to put the 3.6 in several other cars (the new malibu gets it, I think).

The 3500 is basically the same as the 3100/3400 in the fact that it is light weight, and compact in size. The 3.5 Shortstar will probably not fit in one of these cars because of the wider splay of the cylinders front to back. The rear will probably hit the firewall, and the front will hit the radiator. If the shortstar would fit, then it would not take that much more to get the northstar into one of these cars.

[3100 MPFI]

i forgot to add that the 3900 would probably be a good idea as well, but I know the NON VVT 3500 can be made to work on an older computer, but the 3900 will require you to use the newer computer and components.

[communityracingchallenge]

I am fully expecting to have to rewire the car.

I have great access to a salvage yard.. I can get pretty much anything.

One person recommending taking the sub-frame, motor, trans, axles and complete wiring harness + computer from a 3800 Series II Grand Prix.. and that it would bolt right up.

Another commended doing the 3100 swap.. but using the 3500 intakes.

[3100 MPFI]

the 3800 is a 90 degree buick engine. It is an iron head MONSTER. Yes, it has some power to it, but what you gain in power, you lose with the weight you are adding from the iron components.

I don't think the GEN 2 subframe will bolt up. I think it is too different.

if I was going to do an engine swap, I would look for a 3400 or 3500. The 3400 is just as plentiful as the 3100 is, but it has more power and more displacement right out of the box.

[communityracingchallenge]

I got a PM where a person said that using the 3400 motor.. with 3400 RWD pistons.. and a 3500 intake would be the best bang for the buck..

And that the 3400 motor will fit into the 3.1 cradle easily ?

Anyone confirm/deny ? Recommendations ??

[3100 MPFI]

I can confirm that for you,

My gold car is a 1988 Cutlass Supreme with a swapped in late 1999 early 2000 3100 SFI from a Malibu.

The 3400 uses the same mounts as the 3100.

The 3100 uses the same rubber mount as the 3.1 MPFI (although I recommend getting a brand new SOLID RUBBER one from NAPA), but the bracket it is mounted too is different. I think I got the bracket from GM for only $10.00.

You can also use the stock transmission, but i recommend the 1991-1993 4T60-E from a 3.4 DOHC car, or a manual tranny.

[communityracingchallenge]

okay.. I'll bite, why the other tranny ?

The other stuff.. is this a simple tear down ?

[Joseph Upson]

the 3900 will require you to use the newer computer and components.

The best option, but not a requirement, video of the latest test drive on pg 9:

http://60degreev6.com/forum/showthread.php?t=37902

CNCguy has two threads on his work with this motor as well.