high compression setup

[geldartb]

borrowed this from my post in another forum topic.

You can go with MLS headgaskets at .030 and 3.4 gen1 iron head pistons for .040 quench (stock gasket is .040 and .050 quench on iron head) but then you end up with 12.73:1 static compression with 3500 heads. If you run .060 3500 head gaskets you end up with 11.5:1 and .070 quench. The 3.4 DOHC had .070 quench stock believe it or not at 8.81:1 static compression. If you use the pistons from that you'll have even higher compression.
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ok so lets say i go with the 3.4 ironhead piston and a 3500 MLS head-gasket with a thickness of .035 and get a CR of 12.52.1 with an ideal quench of 0.045 ill be good right. i already picked up the piston way back when i first swapped the newer 3400 in.

so trying the 3400 head-gasket bore of 3.75 vs the 3.80 of the 3500 it brings a 12.56.1 CR not much of a difference there and it doesnt affect the quench. ok so the MLS gaskets are actually a 3.72 bore for the 3500 but still that only brings it up to 12.58.1. ive been playing around with this for awhile and never got a positive answer from anyone on waht would work without problems.

ok if this will work without giving me problems and by problems i mean valve to piston contact and other ill effects. this setup would give my cam the high compression it wants and would make it perform nicely and keep me from buying a different cam with all those new profiles available.

just picking you guy's brains to get some plans together.

[bszopi]

I remember Dave having valve to piston contact with iron head gaskets (0.040"), so that makes me think you have issues with the 0.035" gaskets.

[IsaacHayes]

Brad, Dave has a full 3500, and running .040 gaskets brought his quench down to 0.03 which is too close for comfort. His pistons didn't hit the heads though, but the valves did kiss them. He has a long duration cam though too.

The above is referring to a 3400 with 3.4 iron head pistons and 3500 top end. The iron head pistons don't come up as high as the 3400 pistons, so lowering the heads with a thinner headgasket will bring it back down to stock quench... Shouldn't cause any valve interference problems unless your cam would hit on a stock 3400.

[geldartb]

cam doesnt hit as it sits now. so thats good.

according the the CR calc on site here it would give me a .045 quench. which according to that it's still in the green.

prob wont be getting the gaskets for a few more months. would it be wise to replace the bearings when im swapping the pistons out. the ones in there dont have many miles on them but i dont wanna cheap out and screw myself later.
i remember Dave's post from before.

[IsaacHayes]

If the bearings are cheap enough, or the originals look bad, go for it. Plastigauge it though.

[geldartb]

yeah ill definitely plastigauge it though.

i was just figuring if im gonna be in there anyway and already have it apart. they shouldnt be wrecked or bad the engine prob has something like 11k on it all together right now.

$30 for the set of sealed power bearings from autozone. im gonna spend the next few months gathering gaskets and stuff and dive into it early next year.

[Superdave]

Brad, Dave has a full 3500, and running .040 gaskets brought his quench down to 0.03 which is too close for comfort. His pistons didn't hit the heads though, but the valves did kiss them. He has a long duration cam though too.

I just pulled the engine apart and there was a mark on the one "new" piston as well.. this time i was using stock headgaskets.

[geldartb]

so with that being said Dave what's a good headgasket to use so that wont happen.
even with the .035 hedgaskets the CR calc said the quench was ideal and still at 0.45.

what's the max RPM your hitting Dave.

[3400-95-Modified]

As you noted earlier though I think Daves issue is more his duration and ramp rate on his cam... He has it pretty damn close to the limits.

[IsaacHayes]

Dave, tell that rowdy cam to settle down!!!! LOL...

Looks like the duration & high RPMs needs some valve reliefs... Now you really have an excuse for custom flat top pistons with valve reliefs!! Go for ~12.5:1 compression and you should be good with dynamic compression. If it all works out in theory, 12.4:1 would be bled down the same levels as a stock motor with your cam, which you would think could then still run on 87 octane!

EDIT: Damn ninja's snuck in above my post!! LOL
Brandon, if your cam is not hitting the pistons now you should be fine with the camaro pistons and a shorter headgasket. Right now your 3400 pistons come out of the block and with the .060 headgasket you have ideal/stock quench. Camaro pistons don't come out of the block so you need to lower the head down to keep the space between the heads and pistons the same (quench). Since the space between them will be the same (or .005 less) you will be fine. You're just moving everything down more to get the same end result.

Ideally you'd just have custom pistons made based off of the 3400 piston deck height/etc and just have more material in the dish to raise compression. Custom would also allow valve reliefs and flat tops for added benefit of quench as mentioned above, but the cost is a lot higher than dropping in the camaro pistons of course.

[geldartb]

yeah as noted Dave's issue is his duration and ramp rate on his cam plus the rpm and stretch of the rods at higher rpm's.

with that taking into consideration i should be all set.

im still gonna have to address the transmission too. its holding its own right now.

[60dgrzbelow0]

...I just pulled the engine apart and there was a mark on the one "new" piston as well.. this time I was using stock head gaskets.

Well Dave ...there can only be one other answer as to why this is happening....

[Superdave]

Lol...


my limiter is set to 7K, i usually shift a little before that.


I do have a lot of exhaust duration and the lift is pretty high. Maybe tonight i'll make a pair of solid lifters, toss one of the heads back on and a few tootsie rolls on the piston.


I'll post the numbers sometime soon.

[geldartb]

iirc my limiter is set around 6500-6600 although i havent taken it much above 6200ish right now.

sacrificing the tootsie rolls for the engine.

cool looking forward to the numbers.

Lol at the pic.

[IsaacHayes]

Bradon, what is your intake valve closing ABDC ? I'm wondering what the 12.52:1 compression will be actual with your cam.