Meclint69

Okay so I am building a 2005 LQ4 to go in a 1991 Chevy regular cab step side 2wd pick up. I have a T56 to put behind my LQ4. I just picked up a good used set of 243 heads, that have Comp 918 springs installed on them. I want a good streetable truck. I will be running the GMPP carb intake a 750 Holley 4 bbl and the MSD 6LS box. The truck currently has the factory 10 bolt in it with 3.42 and a lock right locker. I am building a Ford 9 inch to put in it, it will have 4.10 gears and either a limited slip or locker. I am going to replace the pistons in the engine and was wondering if i should go with a set of LQ9/LS2 flat tops to get more compression, or is this not necessary. Also I am not sure what cam I should run. My budget is basically nothing so I am going to go with hypereutectic pistons , reuse the factory crank and rods. I will replace the rod bolts with ARP bolts. I am a member on about every LS forum on the net and have read that a lot of guys are running either an LQ9 with 243s or a LQ4 with flat top pistons and 243s. But when I crunch the numbers the dynamic compression ratio is 9.5 to 1 or higher. Everything I have read says the max for pump gas and street use is 8.5 to 1. So can you recommend a cam that will work in my application? I want the truck to have a pretty rough idle, but still retain good low RPM torque and pull hard to 6000+ rpms. I really appreciate your time and help, thanks.

batboy

iTrader: (6)

You can run 10:1 or more with aluminum heads, a mild cam, and pump gas without problems. Although you might need to step up to higher octane fuel than regular.

Bo185

The LQ9 CR is 10:1 with flat tops/317's to begin with so with flat tops 243's should be 10.9:1 and you will have to run 93 gas. The LQ9 was rated t run 87 but GM recommended 93 in it as well.

Meclint69

Yes the static compression ratio is 10 to 1. I am talking about the dynamic compression ratio. Static compression does not figure in the effects of the cam on compression. Dynamic compression figures the actual compression of your engine which is a lower number than the static compression.