CR Qs

[Charlie240sxt]

Ok i see alot of people running 8.5:1 CR but just here lately i see more and more run 9.1:1 CR so what the deal i tought you had to lower the CR for turbo HELP

[240marcuSX]

you dont HAVE to lower the CR. 8.5 CR is pretty ideal, maybe the people with 9.1 are still saving up to lower theirs?

[MikeMurphy]

it all depends on what boost you plan on running and what fuel you have available. If your looking for lets say 220rwhp for example then the stock 9.5:1 CR is more desirable than anything less. Otherwise your engine can turn into a low compression slug. If your looking at high boost applications, then low CR is the only way to go.

Its all about what kind of numbers your looking for. In lets say a 220rwhp (turbo) situation, a 9.5:1 CR car will beat an 8.5:1 CR car all other things being equal.

[andrave]

the higher the CR the more power you are making, but the more prone your engine will be to detonation...so if you are really careful, you can go with forged 9:1 pistons and make more power (on and off boost) but you will run closer to the edge...

[TrunkMonkey]

do a search on compression ratios and boost. iirc, there was a very long discussion about this a few months ago. (you can search using my screen name or WDRacing's. we had a nice chat about this.) the "necessity" to lower your compression ratio to run boost is a thing of the past.

-demetrius

[WDRacing]

9/1 CR is just fine for boost. The lower the CR the more boost you can run for any specific octane of fuel. Pound for pound, you will make more hp by raising boost and lowering CR. A higher CR makes the engine more efficient in NA form.

Basically its a boost vs. octane battle. I would never run anything over 9.5/1 CR with any plans for boost. But like Demcj said, we had a large thread about this same subject with quite a few different theories.

WD

[WDRacing]

Here's the thread... http://www.nissaninfiniticlub....ratio