I'm working on figuring out roughly what my compression ratio will be with my .015" milled 862's on my LQ4. At first calculation I came up with 11.2:1 and I don't think that's correct. I'm also calculating an estimated 58cc on the heads. Looking for the math wiz's. If I dig for a few more hours I may come up with it, but it's not easy. The LS1, LS6, and LQ9 info is all over, just not the LQ4.

 

10.84:1 assuming a stock head gasket thickness of .052" compressed and 58cc chambers.

 

Thank you. That was what one of my calculations had came out to also, but wasn't sure if that was correct. I wish it were an LQ9, I'd like more compressin yet.

 

LQ9 with 58cc chambers would be off da hizzle!

 

While we're on the topic of compression, you wouldn't happen to have an equation that factors in things like compression ratio, IAT, fuel octane and perhaps spark advance to determine what octane is suitable for a given motor? I'm sure camshaft design also has a play in this, but I'm unsure of just how much...yet.

Basically saying 87 octane is good such that compression is below xx.xx, with IAT's below yyy.yy degrees F and that advance is below zz.zz degrees of total timing.

There has to be a function that explains this. I will look into this more, I'm just throwing that out there until I find a reasonable equation to use as a rule of thumb.

 

11.69:1 or very close. I do not know the specs on the stock LQ9 pistons but I got very close knowing the LQ9 is 10:1, then I took the 71cc 317's down to 58cc (theoretically). 11.65-11.70:1 compression..so ya..."off da hizzle!"

 

one of the guys who help me put in the LQ9 asked me if I wanted to stick my 4.8L heads on it LOL

 

What would be nice though is a stock set of 243's. The 64.45cc chambers and stock head gasket bring an LQ9 down to a very street friendly 10.8:1 with no change in flow from the 317's.

 

nope, LS6 heads bring it to 11.1:1

 

I calculated 10.8:1 using math and my TI-89 so check your sources. I just did it again to double check...10.8:1. Did you remember to factor in a gasket?