Compression Ratios

[Ryanscamry]

I understand you lower compression ratio's to lessen the chance of pre-detonation if you have a turbocharger, but what would be the effects if you raised the compression ratio in the cylinders on a naturally aspirated engine?

Would it add more power to a certain ratio and then after that be detrimental or what?

[jwa276]

raising compression does add quite a bit of power. comparing camry v6 engines (3vz/1mz), the older 3vz has a 9.6:1 and the 1mz has 10.5:1. i own a 3vz and i have been considering running it at 10.5:1. with other top end modifications you can get huge numbers without a turbo. of course for cost effective horsepower, its tough to beat a turbo. im just considering it for the whole less moving parts= less maintenance= more reliability standpoint.

you do risk detonation from raising compression. there is a simple solution though: better gas. the higher the octane, the less likely detonation will occur.

jon

[Ryanscamry]

Sweet deal, that really helped me out alot. I just got done reading an article about raising compression ratio and what not. Basically what I got from the information is that with a better head gasket, a more free flowing exhaust, and better fuel you can get really good gains.

I hear what you're saying about power per buck ratio with a turbo though, and if I completely understood everything involved I would take it up in a heart beat.

As it stands I should probably change my timing belt soon and rebuild the engine. When I do that I'll look at raising N/A power or going turbo. For right now I'll probably just raise N/A power for reliability issues. Anyhow, thanks again for the info, its invaluable.

[97_240sx]

Um. You don't get THAT much more horsepower. I've been in about 12 difference compression radio's on frankenstien civics and the difference is not a ton, between the sotck 10ish and uber high 12.5 you might pick up 8-12 hp on a 2 liter... so if you take that to the 3 liter and play around you might make 12-15. And then you have to start wondering about stock rods etc etc. High compression is really not ideal for a lower revving engine anyways. If you were gonna port and polish, port match and re-balance the crank while screwing with hte ecu to allow higher revs, you might see a bigger dif, but the bigger dif is prolly still the 15hp I said above. IF you wanted to play around, see if you can find a thinner headgasket or something, then if you feel like you made a difference work from there.

Big gains from NA means more money then turbo. A perfectly balanced engine, and higher revs...