My dad wants to put the original (number) heads back on his LS5 and he recently got a hold of a set that are completely done up. Stainless valves, hardened seats, 2.19/1.88's, etc. that flow 312cfm if I remember correctly - fresh from the machine shop, never installed (since the port work). Anyway, we're going to freshen the motor up, but we have no clue what is in there right now. From what I've read of 049's, domed pistons are almost a must to make any kind of power, so we can pretty much count on them being in the block right now? I realize that we're going from open to closed chambered heads, so that fact alone would make it necessary to switch pistons, right? That is all assuming that the person who built the motor before did actually put something other than the stock pistons in it...which seems to be a safe bet since the car pulled a hair over 400fwhp on the dyno. I just want to determine if we'll have to change pistons.

This is going to be his and my first engine rebuild, so we're learning as we go. I've started reading some books to get up to speed before we do this...it won't be until late summer or early winter next year, but we're just trying to get some ideas now. Feel free to straighten me out if something I said above is incorrect.

Thanks,
Mike

Mike,you'll need to confirm what pistons you have when you remove the heads.A great piston to use with the original 290 heads would be these:
http://store.summitracing.com/partdetail.asp?part=STL%2DH426CP30

Thanks for the info! Are those things going to be strong enough though? I was under the impression that we should be looking for forged pistons rather than hypereutectic. I'm guessing the ones you mentioned would put us in the stock 10.25:1 compression? We were hoping to run at least 10:1, if not 10.5 or even 11 if we were able to get away with it on pump gas (again, we're still trying to figure this all out).

we DO need new pistons though, right? Thanks again!

Just for reference the stock LS-5 pistons were cast, so if they're still in there, they'd do in a pinch. But hypers or forged would be much more desirable. The cam you run will be a big determining factor on the pistons you run. Do you have the specs on that? Also if you can get one of the head comb chambers cc'd, that would be a big help too in order to see what you're starting with. While the heads are off, measure the deck height at TDC, which will also figure into the CR. Back to the pistons, if you can measure the dome height, I can look up the equivalent Speed Pro piston in my catalog to see what the net dome cc's are. To measure the dome height and deck height you need a dial indicator and stand made for checking deck heights.

Originally posted by DU302:
Thanks for the info! Are those things going to be strong enough though? I was under the impression that we should be looking for forged pistons rather than hypereutectic. I'm guessing the ones you mentioned would put us in the stock 10.25:1 compression? We were hoping to run at least 10:1, if not 10.5 or even 11 if we were able to get away with it on pump gas Strong enough?! LOL ;) I run them in my motor (461 CID),so durability is NOT an issue..with my #215 heads cc'd at 101 and these pistons with a .008 deck height,I'm at 10.59 to 1 or so..my motor runs fine on pump gas with 200-210 lbs/cranking compression..nothing wrong with hyper pistons..FYI,the dome is a hair taller (.100 vs .095) than the TRW L2399 forged piston.You won't know if you'll need to change pistons or not until you confirm what you have in there to begin with..