Questions about heads/intake, etc.

[PCGUY112887]

I have a 96 GP Sedan with the 3100, about 112k miles. I think my LIM is going... so I figure when I have the top off why not go to a ported 3400 lower and ported 3500 upper with the 65mm TB from here.

Then I keep thinking as i'm waiting for my GM service manuals to get here, I could try to do my head gaskets while i'm down there so I don't have to worry about it. But while their off... why not have them ported here?

Ugh what simple things lead to

Anyways, is it even really worth it to have them ported? What kind of gains am I looking at with level 1 porting with LS1 springs and 3500 valves? I could go to 3400 heads, but would it really matter if their both ported since the 3400 heads are only a tiny bit bigger and they'd wind up even when finished? (easier and cheaper to stick to my current heads).

I figured I could get the heads decked as much as I can as well to get a compression boost.

What if I just did my head gaskets and the lower/upper intake/TB, worth it or not?

Thanks!

[SappySE107]

I couldn't tell you what HP gains you would get since I haven't dynoed and I refuse to guess. I can tell you that the 3400 heads are superior in casting and even ported the 3100 heads will not be equal to 3400 heads ported (not only because of the larger intake valve on the 3400). Stock 3400 heads would be an upgrade for your car.

Obviously I could port the 3100 heads, as I have a set here that I could port. I could also add material to get the same shape as the 3400 castings but that would probably cost more in time and reworking than to just get a good set of 3400 heads.

Really depends on the budget, and I see what you mean regarding one thing leading to another. I would probably go with ported heads, stock 3400 lower, stock 3400 plenum and a larger TB (at least 56mm stock 3400). That way you can always do the manifolds later. Sure beats ported manifolds and TB and then taking all apart to do heads if you want that later. Besides that, the valve springs get weaker with age so it wouldn't hurt to replace those, and the valve seats/valves will start to leak after a while due to pitting (mostly exhaust valves for this) which causes a loss of performance. Manifolds don't wear out, just the gaskets.

[IsaacHayes]

Sounds like what I'm doing. Only mine is a 94. Why are you doing your head gaskets? Those don't leak unless something is wrong with your car. It's the LIM gaskets that do. Leave those alone as it will just cost you $100 or more for bolts and gaskets and getting the heads checked.

If you are going to swap heads for performance, best bang for your buck is to get a cheap set of 3400 heads, they flow better (match up better to 3400 lower manifold) and have larger intake valves. IMO porting your stock 3100 heads is not worth the cost. Cheaper to just slap 3400 on there and call it good if you want to mess with heads without going too deep in the pockets. Put the money towards boost or something later. You do have a ODBII computer so you can tweak it with a DHP tuner.......

If you're not swaping heads, leave them on and forget about head gaskets. (unless you have a problem...)

You'll soon find out if you get out the calculator, that it would be cheaper for you to drop in a complete 3400 than to swap heads/etc on your 3100. (and you'd get more displacement, and a fresher motor) That's what I found out, so I decided to just do the intake manifolds. You got to step back and look at how deep you are getting into things and if you are taking a harder/costlier approach.

You will see a nice boost with the 3400/3500/65mm TB. Since you'll have that stuff off already to replace the LIM gasket, it makes sense to swap to it. I'm expecting/hoping ~20hp to my motor. Going from the small port to large port AND 3500 should be a big difference. You'll have the 65mm TB which the 3500 was designed for that size. I'm just using a 56mm due to cost reasons. So in theory you should make even more power.

Do a nice fender well cold air intake with a K&N cone and you'll have quite a nice increase.

Do exhaust next, and an UDP, and you'll be satisfied for a while.. Then do 3400 total swap, cam, or boost or what not if you still hunger for more. Remember you have ODBII, I have un-tuneable ODB1.5, so I have no easy tunability option for anything, boost or not.

I just can't justitfy the cost of building up the small port 3100 when you could build up a 3400 (or just swap it in) which comes with better stuff from thet get-go.

So my advice is if you're serious, put in a 3400 and port that stuff if you must. Otherwise save your money and just swap the intakes if you want a little power with your maintenence. Check out my thread 3500 swap checklist for ideas.

[PCGUY112887]

What does it take to get say 00+ 3400 heads on a 96 3100? I think I read something about a temp sender, but that's all i've seen. I got my manuals in the mail today and it looks just like a few bolts and the heads pop off (doens't look like the exhaust mani's have to come off, just unbolted from the heads?)

I could just swap in some 3400 heads, then 3400 lower and 3500 upper (keeping most things stock, maybe having the 3500 done here since it's fairly cheap) then find a 70mm TB? This way I could save money for an underdrive, or a DHP, or suspension.

I also plan a ram-air intake from the air dam, I had the molded piece of PVC I made mounted in there however today I went into a parking lot that went up at an angle and wacked the air dam and the piece poped out so I gotta find a stronger way to mount it...

Edit - Oh yeah about the head gaskets, I thought it was common for them to go out after so long on the 3x00 engines? At least after reading for a while on clubgp it seems that way, not as common as the LIM but still common after 140k+ miles or so.

[SappySE107]

They use a 3 wire temp sensor, though I thought that was normal for gen 3. Swapping heads is pretty easy. I pull my manifolds out but you could try to leave them in place if you take the studs out of the heads. Its really not that hard to pull the manifolds though.

Don't use a 70mm TB. It requires porting the plenum and it will make driving the car harder. Its just too large.

Head gaskets can last over 200k though so as long as you never used the dexcool crap they could last quite a while. It wouldn't hurt to replace them but at the same time, there could be no reason at all to do it.

[PCGUY112887]

For some reason I thought that mine had the 3 wire sender in it, but the newer ones didn't have the hole for it?

The car has had Dexcool in it it's whole life, that's why I always have a fear of them going .

If I can find a pair of cheap 3400 heads I think i'll slap em on. Is there any gasket between the heads and the manis?

Sorry for all the Q's but what could I rip a bigger MAF off of that would work on my car? I assume the stock one is 52mm like the TB is... or does it have to be replaced at all?

Thanks.

[SappySE107]

Yes there are gaskets between the heads and the lower intake. No, your stock MAF is fine. Stock 3400 TB is 56mm.

[PCGUY112887]

Is there any gasket between the heads and the manis?

And I have the 3100 with the 52mm TB.

[IsaacHayes]

Your 96 has the 3 wire ECT sensor I believe. So does 97-2005. No problems there. It's the 94-95 3100's that had a 2 wire for the ECM, and a single wire in the head for the gauges. Later they changed to the 3 wire all in one, and got rid of the single wire in the head for the gauges. For those cars, the easiest thing is to put a new 3 wire connector on their harness by combining their 2 seperate harnesses into one. 3400swap.com pdf file explains it better if you find out you don't have the 3wire stock.

Yes your 3100 is 52mm TB. The 3400 has a 56mm. The 3500 plenum is large enough stock for a 65mm, with out porting it. I went with the adapter and 56mm TB for my 3500 plenum, as I can retain my throttle and cruise linkage without modifying it, or having to adapt IAC valve, or dealing with a 70mm TB that gives too much air at partial throttle.

I'm going to port match my 3500 since I hear they are slightly smaller stock than the 3400 ports. I'm going to actually gasket match the 3500 and the 3400 lower where the 2 meet. I'm leaving the lower part of the LIM alone since it's going on stock heads. Since opening up the interface of the 3500/3400 is basically a transition from the large plenum area into the runner, I can't really screw up the velocity as it's just a transition from the large space to a narrower runner. Should help if anything which is why I'm doing it.

I don't know if the 3400 has a larger (56mm) MAF or not. I would imagine that it would swap over fine. I would at least go with the 3400 TB 56mm though. The 60* store has an adapter for the 3500 to use a stock style TB, or their 65mm unit.

Oh you mean gasket between the heads and exhaust manifolds? yes there is. That's another gasket that will add to the cost. Look into a whole engine gasket kit, it has everythign from heads up. Allthough when I was looking into it I priced it and peiced it all together for cheaper than the kit go figure. But I think that was with ebay selling un-used gaskets cheap, which come and go..

Contact onefastV6 for some 3400 heads. You'll probably want to have them decked of course before you put them on and that adds to the cost too. I think he still has 2 sets avalilbe.