will62085

iTrader: (4)

so, we all know the obvious advatages and disadvantages to having too high or too low compression with a FI setup...but what are the limits? for me personally i would like to know how low should it be for max power? i was goin with 8.4:1 but now im thinking lower...

777

iTrader: (21)

I wouldn't think you would want to go to much past 8.5:1. I'd say typical is going to be around 9:1.

nitrorocket

iTrader: (12)

Duttweiler told me that on a 347" motor, any lower then 8:1 would not be good. That is what I chose.

Wet 1

iTrader: (4)

Why go so low? It's hard to keep the heads down on an LSx engine above 16 psi anyway and you can get there with 9:1... why go lower if you can't add more boost???

Zombie

iTrader: (2)

How much boost you run has absolutely nothing to do with lifting the heads, unless you figure out a way to run over 1000 psi of boost.

Wet 1

iTrader: (4)

So you are suggesting that LSx owners could run 7.5:1 and 30+ psi with no detonation and not lift the heads???

99SS-T

iTrader: (5)

Aye Parish is pushin 22 psi i think and he has no issues. The reason heads lift is detonation. Causes like 10x the stress that regular stroke causes. 9.1 does seem to be pretty good. If you want to avoid having to use meth you could make the CR lower liek 8.5 but ya are gonna have to move quite a bit more air to make the same power. Not that that is a big problem but it takes away from the max you can make with that same turbo. I personally am gonan go 9.1 when i go forged as it seems to be a good middle ground. Another thing of 8.5 is when you are puttin around or going somewhere that ya dont need 900 hp you it is gonna feel like a dog unless it is a big stroker. Well GL man


John

Zombie

iTrader: (2)

No i'm just stating that people need to get the idea that xx boost will cause problems. Boost is irrelevant, technically it is only a measure of the inability of the motor to consume all the air the compressor is making.

Lifting the heads doesn't come from running 30 psi or even 50 psi. Lifting the heads comes from making too much cylinder pressure which is on the order of 800-1000+ psi

will62085

iTrader: (4)

sorry i need to clarify....this will be on an 355 lt1 with trick flow heads...

JZ 97 SS 1500

iTrader: (2)

LT1 is hard to lift the heads on. 8.5:1 is fine. We have 1 extra bolt per cylinder...reason why LT1> LS1 for boost.....LOL