Jbigs268

I have recently been researching and attempting to build an lq4 for a project of mine...i have a few questions about the build..

First off..i want to retain the OEM rod length (but forged) and simply over bore the cylinders by 0.030 to be on the safe side.

Now i will be running the l92 heads and will have them milled down .030 also to achieve a CC size of 65cc. Onto my question..

I want the compression ratio to be around 10.5:1 - 11.25:1, i believe that with a -1cc dish piston with a 65cc combustion chamber my compression ratio will be 11.75:1, is that right? even with the extra .030 bore and factory crank/rod length?

I have been doing a hell of a lot of research and simply have been getting scrambled up with all of the information that is out there, i just need some guidance!

baronsmith98

iTrader: (2)

Google Wallace racing calculators and you can find out your compression ratio by putting in your information. There are also a ton of other calculators on there.

Jbigs268

Thanks for the input!

Is the .030 overbore worth it since i am only getting 6 extra cubes and have a block in good shape?

baronsmith98

iTrader: (2)

If you have then money then go for it but if I was on a tight budget and the cylinder walls looked good I wouldn't. You could get a 4.000 stroke rotating assembly with that .03 overbore and have yourself a 408 stroker but again it just depends on your budget.

mark21742

What kind of cam and fuel are you planning on running? I would forget about looking for the exact static compression, and instead start with your desired dynamic compression ratio and go from there to get a static compression that is needed.

For instance my 408 is 12.5:1 scr, but my cam (intake valve closing point) drops my dcr down to a 92/93 pump gas friendly 8.22:1

Jbigs268

Im not looking for it to be too radical, its staying with EFI and i would prefer it to be streetable but still happy in the higher end of the rev spectrum because it may be going into a 260z datsun, and i want it to be rather tail happy

mcdonald77

iTrader: (21)

I went 4.030 with my LQ9 running oem flat top type pistons. My compression is right around 10.2:1 with unmilled l92 heads.

If I did it again, I would went with a 4.010 to leave more space for later.

low2001gmc

iTrader: (148)

with milling .030, youd be right around 11:1 but i would recommend milling .015 and running a cometic .040 and still be around 11:1. cometics will help with quench and preventing detonation. by milling .015, it wont affect head flow as much and still leaves you room to mill more in the future if need be. just my 2 pennys. good luck with your project.

niscur29

I didn't touch my cylinders except to hone them on my LQ9. My machinist said they were still within spec so I left the walls alone to allow me some room should anything happen. I went with new 243 heads instead of rectangle heads because I felt they gave me what I was looking for instead of the newer heads.

96capricemgr

iTrader: (1)

Why would you even consider stock length forged rods and new pistons. If spending the money on rods and pistons why limit your selection like that?