3.4 iron head compression

[sbc350]

Hello, I was wondering how to increase the stock camaro 3.4 compression ratio. How much the compression would be with the doch pistons and stock heads? rockauto seems to sell 2 different pistons for the doch engine.


ENGINETECH P30206
Flat top; 1.457" CH; Use C92116 rings

and

SEALED POWER H684CP {#H813CP, WH684CP, WH813CP} DUROSHIELD skirt coated piston; Hypereutectic

.9054" Pin Dia.; 1 Ring; 1.20mm Groove; 1.50mm Groove; 3.00mm Groove; 1.464 CD; Domed Head .040 high w/ 4 valve reliefs

Any experience on these?

[sharkey]

i dont have any experience on this but looking at the specs the dohc pistons have a higher compression height by .014". the compression calculator on this site shows the 3.4l ironhead piston has an 8cc volume and the 3.4 dohc pistons are 5cc. it also shows deck clearance specs, and going off those compression heights it will put the piston .0045" out of the hole. plugging everything into the calculator shows 10.31 with a standard bore, 10.5:1 with a .040 over bore. if you go up to the gen 3 head gaskets ytou can get the compression under 10:1

[Guest]

Raisng SCR on an iron head engine will gain you nearly nothing. I mean yeah, you might get a few ft/lbs and a few HP, but the real bottle neck is the heads and intake.

If you really want to open up the engine put 3400 or 3500 heads and intake on. This is commonly referred to as a "hybrid". Since you're planning on swapping pistons anyway, installing some FWD pistons from teh 3400 will keep the SCR around 9.6:1, dependng on how much teh heads and/or block get planed/decked and will respond better to any cam swap you might have in mind as well.

Iron heads are just a poor choice for any type of performance build.

[sharkey]

as someone who spent the time building an ironhead years ago, i have to agree. the iron heads just dont breath well, even ported. i think things would be better with an aftermarket carbed intake manifold, but the efi manifolds are a huge restriction. more compression wont help much.

[sbc350]

Thx for the info! I wanted to increase the compression because I use e85 fuel. It works better with higher compression. The engine is in '88 s10 blazer so it wont be fast anyway I'm keeping the TBI so I don't want to change heads or intake.

[sbc350]

This just happened. Found 2 cracked pistons. They made a noticeable sound. Going to get these pistons since they have the same compression height and smaller dish than the stock camaro pistons have:

https://www.rockauto.com/en/moreinfo.php?pk=5543103&jsn=4169