SSweet98SS

alright guys, this is my first post so don't bash too much but I definitely need help.
a little back story on the car. I purchased a "98 SS" a couple years ago. I'm now in the process of a cam swap since a lifter went bad. figured why not. while in this process I discovered it had 706 heads on it. Figured what the heck a little bump in compression never hurt anybody. Upon further digging I found out the motor was swapped to a LM7 5.3. Pissed off and depressed I took the heads off to send to the shop to have resurfaced and tested, and theyre cracked, so now I'm sitting with my car tore apart and debating on downing a bottle of sleeping pills lolol jk
so now I think I got a little over zealous and purchased a set of 243 heads that were off of a GTO, the guy didn't know the year(he bought them from someone). Ive been reading and basically need to know straight up if these heads are going to work or not. Ive been seeing people say to mill the heads, ive been seeing people say ill be fine. It has dished pistons. I bought a 224r .600/.600 112 cam, new lifters, 7.40 pushrods, new springs, I believe the head gasket is .051 mls. will I have issues? do I need thinner head gaskets? somebody please help.

JoeNova

You can mill them .020" and you'll end up back at stock 5.3 compression.

SSweet98SS

Ive been seeing 0.30, not saying youre wrong. Would either of those cause clearance issues?

SSweet98SS

Is the bore on the heads too big for the block?

JoeNova

Lots of 5.3s came stock with 243 heads.

NewOrleansLT1

Put the 243's on and go turbo lol..

StealthFormula

iTrader: (35)

No sir, the L33 5.3 motor came stock with 799 heads (same as 243's) and they work very well.

SSweet98SS

so if i dont mill the heads and use .40 gaskets with the 3.91 bore would that be safe? or should i just get them made for the same bore as the block?

JoeNova

Safe for what?

Are you asking about compression, or PTV?

SSweet98SS

both actually. Compression as far as the bore and ptv with the thickness.

JoeNova

PTV isn't really any issue with dished 5.3 pistons.
You can swap in flat top pistons from a 4.8 and you'll have around 10:1 compression with 243 heads on a 5.3.

SSweet98SS

so i wouldnt even have to worry about the clearance if i had them milled??
thank you by the way for all of your input i really appreciate it man.

JoeNova

I've ran .620 lift on a flat-top 5.3 a few times with no problems.
Anything over .600 lift on stock heads isn't worth the hassle since flow numbers drop off above .600.

SSweet98SS

so pretty much what youre telling me is that i dont need to worry about clearance regardless if i get them milled and get the thinner gasket?
i was wanting to mill them and get the gasket for the CR so it wouldnt be like a slug.

Mattlm7

im Building the Same Motor with almost the same specs as above. But my question is push rods !

RB04Av

The answer is MEASURE!!!

Doesn't matter what anybody else came up with in their build. They're all DIFFERENT, once they're not factory stock.

MEASURE MEASURE MEASURE MEASURE MEASURE MEASURE MEASURE. It's the ONLY way you'll be assured of getting it right.

Mattlm7

ok 10/4. 243 heads Milled .20 , mild cam , ls6 springs, truck intake. Summit ls1 Head gaskets. Ls7 lifters 0.80 wall push rods high volume oil pump. Vengeance tune. Thinking of the ls1 intake and injectors. Long tube headers. Should make decent power ?

SoCalDave

Take the 5.3 out and have it bored to the size of a 5.7 liter ls engine. Then install the 243 heads and there you have your iron block 346.

Erod579

I was gonna suggest 383 stroker!