groundczero

iTrader: (2)

I have a 408 cu LS1 with some patriot 5.3 heads on it. I am running a customer ground cam with about 610 lift and 238 duration.
I am looking at the GM ported LS3 heads from jegs
http://www.jegs.com/p/Chevrolet-Perf...11558/10002/-1

The only concern I have is the 5.3 were milled so they have a 58 cc chamber and my comperession is around 11.8:1

The LS3 heads have a 68cc chamber so I will be loosing compression but picking up about 30 or so cfm at 600 lift.

Is it worth milling these heads to make the chamber smaller and bumping compression, if so how much, or just run them as is?

mark21742

Yes I'd mill them. I'm not sure how much can you take out of them though. If you can was ground for the 5.3 heads it will work, but not be optimum for the ls3 heads.

If your going to do the swap I'd spend the money to have the ls3 heads milled and ported...why leave so much possible flow and power on the table by not porting them?

What pistons are you running now, flat, dished, or flat with valve reliefs, and if dished or reliefs what cc are they?

If you just bolt the ls3 heads on I think your engine will feel lazy in the lower and mid rpms compared to your 5.3 heads now.

Raven02TA

iTrader: (11)

take off .030. which is just about what everone does with l92 or ls3 heads.

groundczero

iTrader: (2)

What does that bring the combustion camber to?

Mark I get what you are saying, and I figure a cam swap would be in order also, but these heads will pick up another 30 or so cfm on the intake which is pretty big, these are already ported by GM.
They are a dished piston, I forget the exact amount (I think 20 cc, need to check the paperwork at home).

Raven02TA

iTrader: (11)

Should be at 63cc with .030. The stock ls3 head is 68.4cc.....

for every .006 taken off is 1cc

groundczero

iTrader: (2)

Ok I just checked the build it is dished 14cc pistons.
The cam is 600/610 lift 240/244 Dur 113+3 LSA.

I am wondering if I can go 0.04 on the milling and get even more compression, or is that going to give me problems and just stay at the .03.

KingPin1094

iTrader: (12)

i would definitely try to get back near 11.5:1 compression. thats what i wanna run with my 408.

mark21742

I'm running 12.5:1 scr in my 408 with a 255/271 .624/.634 115lsa cam on 92/93 octane pump gas and full timing. 8.22:1 dcr

groundczero

iTrader: (2)

Mark what size combustion chamber do your heads have, which heads are you running?

mark21742

57cc chamber...in heavily worked over 241s