3.1 head swapping

[jamescmc]

so ive read literally about 100 pages of this forum and am still confused. thought my own thread would help strighten me out. i have 89 gp, 3.1 mpfi. that would be gen II correct? if so, im also reading i should swap to the gen III heads that could be on anything from 95-00? on that note do i go L82 or LG8? and then there's something about using the intake manifold also off of one of those years because the one on what i have doesn't compare how much it flows. please lemme know how im doin and if somthings missing straighten me out. i would also appreciate not being called an idiot or something, im just trying to learn. besides, i want to leave all my friends v8 trucks and one of their 302 mustangs in the dust with my "POS v6" as they say (i hear its been done!) I hope you can sympathize lol.

[geoffinbc]

You are reading about a top end swap. It is a great way to get extra flow in the cylinder heads and intake.

If you do the swap you must use the heads and intake. You cannot use your old intake. The best stuff comes off 3400 or 99 and up 3100 engines.

You can also do a complete engine swap to a 3400 or 3500 if you want but that involves more work and of course more money.

[jamescmc]

ok so it sounds like were on the right track there. what about a port and polish? is that smart or unneccesary. will there be enough to port to make it worth the cash? and then i was reading onwot-tech about some different springs and roller rockers that give even more lift. ill probably be rebuilding a set of heads from a u-pick style junkyard. there are a plethera of gp's. i only want to have to take a set out and put the others in once so its all gonna be done at one time.

[Superdave]

this should give you a bit more background into what's involved..

http://www.domesticcrew.com/hybrid.html


It all comes down to how much money you want to invest into the project, Whatever you do, make sure to research and/or ask when you get your final build plans together. There is plenty of power to be made with these engines however the weight of the car is a big factor as well.. GP's are pretty heavy so it's going to take a little more to really leave your friends in the dust.

[jamescmc]

holly hell, that is just what i needed. thanks so much. i dont think it can be made anymore clearer. hah, its gonna be a good day.

[walterdude]

"99 and up 3100 engines."

To the best of my knowledge most 99 3100s came with small port heads. My 99 has small ports. On the 3100, 2000 and up has large ports. On the VIN there is a letter (M?) that designates the small port cars. Someone should know more about that than me...

Not to argue, but, it WOULD be a nasty surprise to pick up a 99 top end thinking you have large ports and finding out that you bought the same parts you already have.... Wouldn't want THAT!!!
Luck,,,,
Tom..........

[geoffinbc]

Well then go with 2000 up to be safe.

[talon2swords]

"99 and up 3100 engines."

To the best of my knowledge most 99 3100s came with small port heads. My 99 has small ports. On the 3100, 2000 and up has large ports. On the VIN there is a letter (M?) that designates the small port cars. Someone should know more about that than me...

Tom..........

Hmm. I have a 99 Lumina and a 97. I've been collecting parts and I almost have everything I need to do the top intake manifold assembly to 2000+ parts for one car. Only problem is which car should I do first. It would be nice to confirm if the 99 has the large port. I wonder how I do that?

[bszopi]

Does the intake manifold on the 99 look like the intake manifold on the 97? If so, then you have the small port top end. If it looks more like a 3400, then you have the large port.

[talon2swords]

Does the intake manifold on the 99 look like the intake manifold on the 97? If so, then you have the small port top end. If it looks more like a 3400, then you have the large port.

I know the upper manifold is the old style (like the 97). Don't know about the lower one.

I was talking about the heads. Some say they used the "rare" large port heads in 99 (larger intake valve?) before they became standard. I guess I'm confused about this point.

[robertisaar]

Does the intake manifold on the 99 look like the intake manifold on the 97? If so, then you have the small port top end. If it looks more like a 3400, then you have the large port.

basicly, if the manifold looks much smoother, with larger lettering and without all of the lines that go above and below the 3100 SFI V6, right?

[bszopi]

The larger valve heads came with the large port top end. So if you have the small port top end, then you have the smaller intake valves (1.72" vs 1.76").

[bszopi]

basicly, if the manifold looks much smoother, with larger lettering and without all of the lines that go above and below the 3100 SFI V6, right?

Exactly.

[talon2swords]

The larger valve heads came with the large port top end. So if you have the small port top end, then you have the smaller intake valves (1.72" vs 1.76").

Oh, ok. I was thinking maybe GM started using the improved heads with the old style intake before the 2000 model year. That's what I get for assuming.

[bszopi]

No. There were a select few vehicles that came with the newer style 3100 starting in 99. Its kind of like the 3100 was available in a select few vehicles starting in 1993, but wasn't used in the majority of cars until 94.