Circle Track 3.1L (Modded)

[ForcedFirebird]

I have a 91 grand prix, and its obd1. Its the setup I learned to tune on. I can do anything you want to if if you stay naturally aspirated

You have a gen 2 motor, which will look nothing like a 3400 upper intake. You can do a hybrid swap. You have a flat tappet cam, so comp, crane, crower, lunati, etc make cams for it.

You would need a 3400 block to use the camaro or DOHC pistons. camaro give 10.8:1 and DOHC give you roughly 13:1 with 3400 top end.

The 3.1 Camaro with 3400 heads give 12.xx:1 and the 3.4 pistons with 3400 heads give 14.xx:1 according to the CRcalculator IIRC.

Tuning equipment can be had cheap from Moates for your car.

[communityracingchallenge]

I have a 91 grand prix, and its obd1. Its the setup I learned to tune on. I can do anything you want to if if you stay naturally aspirated

You have a gen 2 motor, which will look nothing like a 3400 upper intake. You can do a hybrid swap. You have a flat tappet cam, so comp, crane, crower, lunati, etc make cams for it.

You would need a 3400 block to use the camaro or DOHC pistons. camaro give 10.8:1 and DOHC give you roughly 13:1 with 3400 top end.

Then it must be a 90 Grand Prix, because the connector was a flat 4 pin type prong, not the OBD1 connector.

[sharkey]

in your car somewere there will be a plug like this


all gm's with computers till 94 had that plug. its a standard gm diagnostic plug for gm obd1. if you dont have one in the car (usualy its under the dash on the drivers side) its been removed.

[communityracingchallenge]

I was asked today if I was going to change my fuel injectors to the v8 type, since they flow more and fit right in.

Never heard about that before.. is that an option anyone has tried.

[ForcedFirebird]

I was asked today if I was going to change my fuel injectors to the v8 type, since they flow more and fit right in.

Never heard about that before.. is that an option anyone has tried.

Yep, I have 24# blue top Denso from a Ford Mustang.

[communityracingchallenge]

Yep, I have 24# blue top Denso from a Ford Mustang.

And this is better ?? Come on FF, you going to make me drag every speed secret you know out of you ?!?!

As a further aside.. we lost the 3.1 motor over the weekend.. got hot and siezed up.

So this "upgrade" thread is now a "rebuild" thread.

[Superdave]

ok, so with my limited understanding of circle track racing the basic idea is to have an engine that will be:

A. Lightweight to help with turning
2. Have enough torque/HP to get you up to speed right out of the corners
III. Enjoy high RPM's
D. Look Stock


I can think of a few combinations i'd use, all would be pushrod...

First question, does it have to sound stock? Like if you pull up for Tech and it's idling like a 9 sec dragster would they let it pass? lol


all the Gen3 style engines love the higher RPM's... you can go a bunch of different directions with that.

1. 3500 swap with a blank or large port 3100 Plenum (and maybe a bored TB) With 3500 "header style" manifolds

2. 3400 swap, Camaro 3.4 pistons, 3500 heads/LIM with a large port 3100 plenum, bored TB, 3500 "header style" manifolds

3. Either of the above with a custom ground roller cam. Keep the LSA in the 112-114 range, around .510 lift and 270 advertised duration. Should keep it idling fairly decent.. Also a trick that seems to help is to decrease your spark advance at idle, makes the idle much more "lazy" instead of choppy, might fool a judge...


4. If you wanna get more wild then you could use a '00+ 3100, swap in a 2.8 MPFI crank, 2.8 RWD pistons (.040" overbore) with 3500 heads/LIM and a large port 3100 UIM, Camaro 3.4 headgaskets, decent reground cam and a set of 3500 exhaust manifolds.


For injectors i'd go with #24's atleast.. i'm personally running #32's and they seem to be working very well.

[ForcedFirebird]

4. If you wanna get more wild then you could use a '00+ 3100, swap in a 2.8 MPFI crank, 2.8 RWD pistons (.040" overbore) with 3500 heads/LIM and a large port 3100 UIM, Camaro 3.4 headgaskets, decent reground cam and a set of 3500 exhaust manifolds.

Isn't it going to take more that .040 over to fit the 3500 valves? Ben has some pics of the 3.1 heads gaskets on the 3500 head, and the valves won't clear.

And this is better ?? Come on FF, you going to make me drag every speed secret you know out of you ?!?!

No secret, I need bigger injectors (than stock) to fuel my turbo. Here's some more info...
http://www.rceng.com/technical.htm

You are going to have to tune for the larger injectors, or the car won't even idle.

[SappySE107]

The valves will clear without doing anything. The combustion chamber is bigger than the bore thoug which was the issue.

A 1990 is OBD1 still. Don't just put bigger injectors in there.

i would use a crank scraper on your next motor setup.

[Driver_10]

Hey circletrack, forced firebird waz up! Glad to see you two!

[ForcedFirebird]

Hey circletrack, forced firebird waz up! Glad to see you two!

I've been here longer that *other site*, lol.

[Superdave]

The valves will clear without doing anything. The combustion chamber is bigger than the bore thoug which was the issue.

A 1990 is OBD1 still. Don't just put bigger injectors in there.

i would use a crank scraper on your next motor setup.

Didn't you say on V6Z24 that a .040 bore on a 3.1 would clear the larger chamber?

[FastZ34Lumina5]

We used to have a 1991 Z24 cav with a 3.1 in it. And we raced on a 1/4 mile Dirt track. We ran a Under drive pully. Also we ran the 3.4 DOHC fule Injectors. In the 3.1 and at a higher RPM it ran better.We also by passed the AC IDK if it did much but it was less weight and one less pully to turn We ran the car right in first gear. It was a auto and we welded the gears to make it a posse and that helped alot. We ran for 10 lap heat race and 20 lap main event. it ran about 6000 RPMS.In first gear. It held together all year and we Dominated. I also have videos to prove this. That this 3.1 V6 ran at that rpm for that long and never had a problum.

[communityracingchallenge]

Good information guys.. though I think there is still some conflicting opinions on the 3500 and/or 3400 heads on the stock 3.1 block.

Dave - in Re to : First question, does it have to sound stock? Like if you pull up for Tech and it's idling like a 9 sec dragster would they let it pass? lol the answer is no, it doesn't have to sound stock. The rules say "stock appearing" which is plenty wiggle room for a pirate like myself. Some of the cars have their spark advance at 36* and they can barely idle.

The Mods I like the best are the ones that are mostly plug & play and don't require boring out the block, replacing the block, mounts, tranny.. things that aren't easily reversible if a tech inspector finally says enough. Chaning heads, intake manifolds, exhaust manifolds, porting out throttle bottles, intake/exhaust manifolds, valve jobs.. those are easier fixed and more tolerable.

And anything which increases compression is a big plus.. not a street car, doesn't have to idle well.. doesn't have to get good mileage, doesn't have to pass smog. My experience is racing fuel, high compression = cheap source of increased horse power.

[SappySE107]

3.4 DOHC injectors in a 3.1 ECM without reprogramming will idle like shit and run pig rich. I want the video.

You aren't running 3500 heads on a stock 3.1 block so I guess that is ruled out.

Run 3.4 camaro head gaskets, 3400 cylinder heads and fuel rail and manifolds and TB.