What factory flat top piston could I use to raise the compression on a stock LY6, and how much will it bump up the compression?
I know the LQ9 has flat tops but I'm not sure if the valve notches will be in the right position.
Thanks
Jarhead

 

Ls2 piston is true flat top, so is lq9. No vr in either from gm. U will have to cut ur own vr if use either piston

 

Thanks
I saw an old Car Craft dyno report where they used an LQ9 short block and put on L92 cyl heads and a .570 lift cam. They used clay on the piston tops to check PTV clearance and had no problem at all.
Anyone know how much the piston swap would raise the compression?
Thanks
Jarhead

 

how about mill the heads? LY6 pistons have Valve pocket for exhaust valve, just need pocket for intake valve(if cam is to big)

thats how I did my 6.0L short block l92 setup.

 

Thanks for the info BES.
So you had to cut intake valve reliefs to clear?
What lift and duration are you running?
My plan was to find some stock flat tops to replace the factory LY6 pistons to raise the compression a point or so.
I believe the LQ9 and LS2 pistons are about the same although the LS2 has a narrower compression ring.
Yes I have considered milling the heads to increase the compression but I want to use a .570 or so lift cam and I don't want piston to valve issues.
Thanks
Jarhead

 

my cam is 242/246 655 620 on a 108lsa. heads were milled .070" and intake milled to match(single plane GMPP)

we put .100 cut into the piston for intake clearance.

 

WOW! That's a big cam.
So you milled the heads .070, what compression ratio did that give you?
How much total can be milled from those heads without weakening the decks?
Jarhead

 

I fully intend to cut .050" from my L92 heads, I dont think I will need to mill the intake, but I will need to oblong the bolt holes. should give me 11.0:1 with a .040" gasket and stock LY6 shortblock.
YES I will need to cut valve releifs in the pistons, probably around .100" like BES did

 

Thanks for the input 3pedals I do like your Camaro and how it runs.
Low 11s is pretty impressive.
So how big is your "small" cam?
I plan a combo pretty much like yours, an Ly6 with a carb, cam and headers.
I've never been good at shifting a manual tranny so I'm going to run a powerglide or T400.
Jarhead
PS With that 120 speed I think you'll get into the 10s.

 

Cam is presently comp 227/ 235 @.050", .613, .621 114+4. it works well but I believe there are better choices for a carb app
Thanks for the compliments

 

just over 11 to 1 with a .054 cometic gasket.

my SS went a best of 10.93 at 126 1.44 60 ft, 6 speed car, 3820lb raceweight. and I shift it 7700.

the small attention to details (morel lifters, hollow stem intake valves, manley nextek spring) all show up on the dyno and at the track.

good luck on your L92 setup

 

Thanks a bunch for the information.
I just bought a set of LS2 pistons and rods from a member here and I will put them in my LY6 when I get it.
If I've figured it right I should end up with about 10.9 to 1 compression without milling the heads which is about where I want to be.
Jarhead

 

effectively what you are doing is putting l92 heads on an ls2, iirc 10.9 to 1 is stock ls2 compression, your actual compression is going to be closer to 10.1 unless you mill the heads

 

Thanks, I was basing the 10.9 to 1 estimate off of the Car Craft dyno test where they used a LQ9 shortblock and said the the head ccs of an LQ9 and L92 was the same and the compression would stay at 10.9 to 1.
I guess 10 to 1 isn't bad and will run great on 93 octane pump gas.
My plan is to start like 3 Pedals did, stock shortblock LY6 with MSD controller,carb and headers, using the stock cam with a new timing chain and front cover to replace the VVT stuff.
Then after running awhile, pulling it down for a new cam, ported heads and the LS2 pistons and maybe milling the heads to up the compression some more.
Jarhead