Okay, here's the plan:

I am having a 402ci stroker LS2 built for my car. Forged internals, custom dished pistons, etc. I also plan to add an STS Turbo to my car sometime in 2006.

My first thought was to put on a set of ported LS1 heads that I already have onto this engine. The engine is being built for a 9.5:1 compression ratio, and with these heads (which are heavily milled) I would end up with about 10.8:1 for now, while it is normally aspirated.

However, I got my hands on a little extra cash and am considering getting better heads and putting them on NOW. The heads I am looking at are LQ9 heads (unmilled) and flow fairly well on the intake, and EXTREMELY well on the exhaust side.

My dilemma however, is about the CR until I add on the turbo kit. My first question is, how much are these LQ9 heads going to drop the CR?

My 2nd question is, how is the driveability going to be (this is a daily driver first and foremost) for the next year or so, until I can afford to add on the turbo, with such a low CR? Has anyone else run into this situation? I've had a couple people tell me that I'm going to lose too much low end pull with that low a compression - but at the same time, I know their experiences are with LS1 engines with stock cubes, not strokers. My understanding is that the stroker ADDS a ton of low-end grunt, so will this just balance out for now?

Finally, how much is having a low CR going to affect my ability to pass smog when I move to California later this year. I've been told that higher compression reduces exhaust emissions...... am I going to run into a problem here?

Oh - and before you ask, I am not sure yet what cam I am going to run. Probably something in the mid-230 duration range, but It'll probably be a custom cam in any event.

I'm posting this in a couple different forums, because I realize there is a lot of overlap here (FI issues, smog issues, heads issues, etc.)

 

to the top

 

402ci LS2 stroker at 9:1 compression will supposedly have 3% less power than a 10:1 engine.

 

Well, that sounds like an acceptable loss for the interim between NA and FI. Know anything about how it will affect a sniffer test? (Assuming I use a proven-passable cam like a TR224).

 

A 9:1 402 with a 224/224///114 cam will pass with flying colors.

 

not trying to bring you guys off topic here, but what kind of power loss can be expected going from stock LS1 heads to stock LQ9 or LQ4 heads on a 346 LS1?

 

A 7:1 408 stroker motor will make more power than your 10.5:1 346 will, period, amen. I would shoot for lower than 9.5:1 compression, more like 8.5:1.

 

I don't think most folk's butt-ometer can feel a 1/2 pt drop in compression.

 

john, did you just say you were tryin to feel "folks" butts?

 

Either you build a FI engine, or an NA engine. For an FI application I would keep the compression low to max out your power potential on pump gas. I would go 8.5:1 too.

 

Well, I had already ordered the pistons for a 9.5:1 build. However, I just bought some ported LQ9 heads - that should drop the CR done another .5 or so, right?