I found a set of LS6 heads that I'm ready to pull the trigger on, but I had a few questions. I'm keeping my truck N/A for now and will be using it as a weekend toy on the street mostly.

From my research, milling the 243's .030" with a .040" gasket will put me at 9.9-10.0:1 CR. Does this hold true for dished pistons or just flat?

I will be bolting these to my 2003 5.3 in sig. I believe I have dished pistons, as opposed to the flat tops, however, I've read conflicting information on this. Swapping pistons to flat tops is NOT an option.

Would these heads get me to where I want to be if I have them milled .030" even with the dished pistons? Ideally I'd like to be at ~10.5 CR. What gasket would you recommend?

Cam specs- 215/222 .603"/.596" 115.

Input and opinions welcomed.

 

You wouldn't need them decked at all with flat pistons... look at the gen4 5.3 and they use 243/799 heads because GM switched over the pistons to retain the c/r. Decking .030" gets you back to around stock.

Also, I'm not sure, but I'd think you'll have clearance issues with that cam.

 

2003 5.3s come with dished pistons and 862 or 706 heads which have like 61-62ccs. when gm went to the 08 5.3s with 799 and 243s which have 64-65ccs, they also went to flat top pistons to maintain the compression. milling 799 or 243 heads .030 will put you right around 59-60cc bringing you compression a hair up but increase head flow quite a bit. using a .040 gasket would bring compression up closer to your goal of 10.5 but ptv would be become more critical. compression helps with torque so the milling and use of .040 gaskets i would do.

now as for the cam, 215 isnt much on the intake and the 115 lsa would help with ptv and it would have a smooth idle.

just depends on what you want to do with the truck and 5.3 really. what are your goals? do you intend to put a stall and gears eventually or just heads and cam? if just heads and cam, i suppose that 215 cam would do but you still better check ptv to be the safe side. now if you plan to do stall and gears later on, i would think a 220 cam would be best. a tr220 with 551 is a proven cam. a tsp 220 with 581 lift would be good too. some folks get caught up in the lift numbers and lift isnt everything. either one of those cams would clear easier too.

good luck with your project....rob

 

Thanks for explaining that better than me Rob...

 

If you are looking at purchasing a set of cylinder heads, we do offer a stage 2.5 fully cnc ported 5.3 cylinder head that we can mill to match your CR goals and still fit with that camshaft and have great ptv clearance. If you are on a budget these cylinder heads offer great flow (alot more than a stock 243), are a brand new GM casting, have aftermarket stainless steel valves, .650" dual springs, and are still cheap enough to fit most budgets for what all they offer.

Here is a link to our page:
PRC Stage 2.5 5.3L CNC Ported Heads

 

I forgot to mention that another good option would be our Stage 1 LS6 cylinder heads as we can get great flow out of them as well and they start $1199.99 with stock springs and valves.

 

I thought my signature posted, but I see it didn't.

Thanks for the help, Rob.
My cam was spec'd by Geoff at EPS. He said that the high lift would give me more torque down low, which is what I was looking for. I wanted ~10.5:1CR originally for more torque, but I see that probably won't be an option without running into PTV issues. 10:1 CR would be fine then.

Any of the 220 cams mentioned wouldn't help me down low, which is what I need to get my Av moving. I'd also need at least a 3200+ stall TC.

So now I ask- what would get me to ~10:1CR with 243 heads on my dished pistons? Would milling them .030" still be beneficial? What head gasket would I need then?

Jake- thanks for the info. I'll keep you guys in mind if I can't get these heads to work for me.

 

Dished pistons with .030 mill and .040 head gaskets = 9.9:1 (what I currently have).

In a 2003 you'll have dished pistons unless you have the aluminum block, which more than likely you don't. If you have the flat tops it'll put you at 10.5:1 -- ish.

From flow charts I've seen, the stock 243/799 heads airflow seriously falls off after .550 lift. If you have the money, I'd definately start looking into the PRC's that were mentioned earlier.

 

another good thread that will do me some good later on

 

Dmelvin thanks for replying. Do you have a link to those flow charts?

I'm trying to decide if putting these heads on would really benefit me with the cam I have. The PRC's are not in the budget right now.

No one has anymore opinions?