97civixlx

I'm in the works of building a j35 for my civic.

I was just wondering if there was any real difference when you go from 10cr to 11.5cr. I know more compression usually yields more power, but if the amount is insignificant then I'd just leave it be.

This will be tuned in 91 oct.

Thanks!

k20z1ej1

Generally speaking, 3-4% per point. So, in your case, 4.5-6% more power.

97civixlx

So only about 5% more? Haha thanks man.

B20VtecVillain

What these guys are saying, 3-5% is about right for a basically stock engine but with aftermarket parts it can really vary a great deal. Going from 10:1 to 11.5:1 on stock cams with a stock intake manifold and a stock or crappy aftermarket header will likely yield not much of an increase. However take that same compression increase on an engine that has aggressive aftermarket cams, a ported or aftermarket intake mani and a good header that flows very well and the gains will be much more significant. The best power I've personally gotten from an all motor J35 so far at my shop was with an Van J35 shortblock, CL-S (J32a2) heads-ported, ported intake manifold, custom 3.5" intake, TBMW cams, modified DC Sports headers, 3" exhaust. The setups owner, In search of more NA power on a stock short block, decided to have his heads decked and went with a thinner head gasket setup. (previously used OEM) This resulted in a little under 1 full point compression increase but was worth a solid 18-21 HP over what it made previously. On a stock J35 though, simply milling the head and using a high comp gasket MIGHT net you about 8-10HP after tuning around it. It's just like everything else, mods compliment each other; if you can move the air the compression will be a welcome increase, if your choking a bit then more compression won't be quite as useful to the engine.