Compression Ratio

[JJAB]

Guys, I am about to build a 408 stroker motor out of a stock LQ4 motor. In my experience of putting hotrod motors in EFI vehicles, there sometimes is a problem of making the computer(ECU,PCM) and the compression ratio work together and be a "happy couple". Would you knowledgable LS guys here on the board reccommend a compression ration to stay away from? \

I know a lot depends on what I expect out the motor and what I am going to do with the vehicle that the motor is going in so here is the basics. Its going in a SWB truck and I would like to achieve 450 RWHP. So that being said I am estimating that the crank HP needs to be in the 575 to 600HP range. Opinions please??

[BR3W CITY]

Even with a built 4l80e, that seems like a high estimate for drivetrain loss.

I don't think the compression itself would be an issue....if you tune it with HP Tuners, the tuner should be able to setup things like VE tables to have a "happy engine". I'd think you'd have a bigger issue with stuff like knock sensors not liking huge cams.

How high are you trying to go? I've seen motors up to around 11.5:1-12.1 being tuned just fine, provided that they have enough supporting gear (intake and head flow and injector and fuel system capacity)

[whitels1]

I have to agree with BR3W CITY, make sure you are supplying enough fuel, 60lb injectors for what you are doing sounds around right. If you have a good tuner all is well.

[Super73]

My 418 is 12.9-1 and I have run it on 91 octane. Made 511rwhp through a loose converter and glide. That was with very conservative timing, 20* total at WOT. Stood on it quite a bit on the dyno and showed 0* KR. Have also driven it around a few hundred miles with 0 kr. Keep in mind, I have a cam with a decent amount of duration, and my dynamic compression comes in at 8.7-1.

On E48 it made 546rwhp with 26* total timing. Didn't make anymore with 28* or 30*..

FYI, my 60lb injector on E48 are mid/high 60% duty cycle at 58psi fuel pressure.

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