I have to put new pistons in my LS3 and am debating on whether to keep the 10.7:1 or drop it to 9.0:1. I have a LSA blower running about 10-11 psi of boost with a meth set-up. I don't drive the car a lot, so I am leaning toward keeping the higher compression for better performance under normal driving. I doubt I am going to get a lot more out of the blower without upgrading to a larger one.

Opinions?

 

It’ll be fine with meth or e85.

 

yep if you can always spray meth or use say 40% ethanol or more = raise compression

don't want to depend on meth or high E = lower compression

blowers make alot of heat when they sit on top of an engine so be prepared to find all E85 stations
And I am not sure meth is reliable enough in this situation. It would work but it would be absolutely critical which I don't like so I wouldn't depend on it. Use the E version of our favorite alcohol

 

I would keep it unless you plan to up the boost more.

 

With the limited power output of the LSA I would keep the compression up. We put LSA's on 10.5:1 cars all the time with no issues and run more then 10PSI. 10PSI is nothing especially with a meth setup, even on straight pump I don't have issues even at 11:1 until over 17lbs. I wouldn't lower the compression to 9:1 unless you were planning on a power adder that moved a ton of air and you were going to run triple the boost.

 

Thanks for the replies! I ran it a few times with the stock pistons (10.7 CR) and the meth and the knock sensors never kicked in. My max psi is going to be 11 psi and I already have the meth set-up, so I will stay that route.

One other question. I noticed the oil ring on the higher compression pistons is 2mm, and on the lower CR pistons made for boost, it was 3mm. Will the small oil ring cause any issues under boost?

 

Keep it. Been running mine with boost for over 40k miles.

 

Keep it 10:7. I ran 18psi on my L92 for a few years w/ E85.

 

The smaller oil ring will likely perform better.

But neither will matter a damn to boost, as they're nothing to do with boost.

 

They must mean something as a lot of the pistons with a low CR specifically for boosted applications seem to have thicker rings versus the pistons with higher compression that aren't specifically made for boost applications. I thought maybe the boost adding extra pressure could cause the ring to break or allow blow-by. It was just a guess.

 

If boost ever gets as far as the oil ring, you have a serious problem.

More modern designs run thinner rings. Whether 2 or 3mm or whatever has nothing whatsoever to do with boost

 

Why so low? Even at 10.7... bump it up to 11.5:1