ColeGTO

iTrader: (3)

I finally found a LS3 bare block. I'm going to build either a stock rod/stroke LS3 or a 6.125"/4.000" rod/stroke 416. I already have both LSX-LS7 heads and OE LS7 heads in the garage, both need minor repair. I also have a matching LS7 EFI intake.

No, I'm not selling them and going with a LS3 head.

My question is, if I buy aftermarket forged LS3 or L92 pistons, will the valve relief positions in a LS3 designed piston give me hell with the LS7 valve placements?

If I go with standard "rebuilder" hyper pistons, then I'd pick the L92 since they will have valve reliefs, but will they still be sufficient to clear the LS7 valves?

I'm going to be running the GM LSX454 cam because it's free and a decent choice for my 2005 GTO street car build - 236/246 @ .050" and .648"/.648" lift (LS7 1.8 rockers) on a 110 LSA. So I'm certain I'll need some sort of valve reliefs.




Thanks,
Cole

KCS

iTrader: (20)

The LS7 and LS3 valves are in different spots, and with that cam, you may not have the clearance you need. I would suggest checking with a vendor here or one of the piston manufacturers of your choice to see what they say. It's been done, though. You just may need small changes made to your piston.

ColeGTO

iTrader: (3)

Thanks for the info. I'll be calling a few people on Monday.

03EBZ06

FWIW, I just got done w/mods to my LS3/SMALL BORE MAST LS7 265CC head setup. ~640rwhp so far. I'm not sure what those heads would be worth in power over the ones I have on a similar engine.

DietCoke

iTrader: (18)

They'll work fine, even with stock sized valves and placement.

Source: Own engine - 630rwhp through an automatic.

ColeGTO

iTrader: (3)

What heads and pistons did you use in your build?

DietCoke

iTrader: (18)

I used stock LS7 heads worked over, and a small bore LS7 head that is no longer on the market. Wiseco pistons

Patron

Good to see you still around Diet. Cole how did it work out with the post I left over on YB did they say it would work out with the JE pistons as I said?

Also here's 1 again......Ls7 heads on a Ls3 Camaro with factory pistons. Mag has more reading but the pic's tell it all...little fly cutting of the pistons .080 intake and .070 exhaust. .629/.620 cam lift no duration listed. I have the mag.

http://www.superchevy.com/how-to/ght...r-heads-ls7up/

DietCoke

iTrader: (18)

The ls3 heads of today are just as good as the ls7 variety. I only used ls7 stuff because the ls3 support wasnt around in 10/11. If you have ls7 intake and stuff you want to use, the ls7 stuff will work. The oversized valves arent ideal for max power, because of clearance/shrouding, but do not perform poorly, either.

ColeGTO

iTrader: (3)

Thanks for the info.

I was going to see if I could turn the OD of the stock LS7 valve down from 1.615" to 1.590" in the lathe. I know it will narrow the seat width of the valve a little bit (.0125" on width), but I'm sure it would seal just fine.

The big question mark is what it will do to the flow. I'll put it on the flow bench and see how much the two sizes change flow with a 4.070" bore and go from there. I wonder if it won't improve the flow a little by unshrouding the valve from the bore a little.


Thanks,
Cole