1FastBrick

iTrader: (17)

How do you plan to obtain 10.1 compression on a stock 5.3L and 243 heads???

1FastBrick

iTrader: (17)

Since a factory 5.3L is around 9.5:1 with the factory heads @ 61.5 CC chamber and the 243 heads have around a 64.5 cc chamber, You would have to mill the 243's around .030 just to get them back to factory spec to maintain 9.5:1.

The more you mill the heads, the more you comprimise the deck for forced inductions applications.

.030 is about the most you can mill a factory head before you start running into Intake fitment issues...

Now if you open the motor up and stick a flat top 4.8L piston in there You would barely have to mill the heads.

Dont believe me??? Look up the factory L33 option. Its an aluminum 5.3L with 4.8 flat top pistons and 243 heads from the factory. Compression is around 9.9:1

HTH

01silvy

This is info i've needing to hear.. The main reason im doing the heads is because i'm leaking coolant in the block somehow, either by head gasket or a cracked castec(i do have castecs on this engine) so i was wanting to get rid of these stock heads all together. I wont be swapping pistons or anything like that, I was also planning on using the stock MLS gaskets but if i need to run the thinner cometic head gasket and mill the heads .030"-.035" then i would do that.. So to acheive 10:1 and run the stock MLS head gasket i would probly have to mill the 243's around .040"?

Thanks guys

01silvy

Bump, any other ideas?

spent21

iTrader: (3)

Some of the 4.8/5.3 heads had a notch in them that hindered one from using MLS gaskets. I'm not sure if any of the 243's were notched or not, but that is definitely something to be mindful of.

Do you already have the 243's? If not, how much are you planning on spending on a set? The reason I ask is that by the time you find a set and have them rebuilt/milled, you may be able to pick up a good set of 862/706's and have a mild port job done.

TXSZ66AVLANCHE

iTrader: (7)

$27 per piston for new flat tops to much for some added HP?

01silvy

No its not too much at all but all im planning on doing is the heads and cam..doing a head and cam swap is one thing but pulling the entire bottom end and all that is another thing.. if i was gonna do the pistons and all that i would probly just go ahead and do my 6.0 swap.. I've thought about it more and my best bet is to probly just stick with 5.3 heads cause i wont have to mill them hardly at all to get my desired compression ratio..

Since ill probly just stick with 5.3 heads my main concern is i want alittle better flow but will a port job hurt the bottom end power any? I know bringing the compression up will help bottom end too i just dont want to lose any from porting the heads..

Thanks guys

1FastBrick

iTrader: (17)

I am only aware of it being the early 862 heads on the 99 and some 2000 4.8L/5.3L

The 806 early premeter valve covers had the same issue with the nothced area

Here is were That info can be found. Gen III GM Small Block: Engine Builder

243 heads did not have that issue.

Here is a discusion we had pertaining to MLS head gaskets. https://www.performancetrucks.net/fo...gasket-491846/

01silvy

^^^^^^ yeah thats what i was thinking, i dont think the notched heads will be a problem for me.

1FastBrick

iTrader: (17)

No A mild port job would not hurt your bottom end power band.