I have a 2004 5.3 which has a 7cc factory dished piston
trying to decide how much to mill my 243 heads to achieve a 10.0 to 1 static comp ratio

243 heads have a 64.45 cc chamber and it takes .007 to remove 1 cc
milled .042 achieves 58.45cc chamber which i came up with 10.09 to 1 comp
milled .049 achieves 57.45cc chamber which i came up with 10.2 to 1comp

Can someone double check my numbers for me?


These are the numbers i put in the comp calculator
3.779 bore
3.662 stroke
-7cc piston dish
.053 head gasket thickness
3.903 head gasket bore
.010 piston out of the hole
9.240 deck height

 

Welllllll the easier way than guessing is to just plug it directly into the calculator, Engine Compression Ratio (CR) Calculator

Put in all the stuff then at the bottom put in 10:1 for the CR then click calc combustion chamber volume.

According to that you need a 55.034cc chamber for 10:1 SCR. So with your 0.007in per cc, thats (64.45-55.034)*0.007=0.0659in mill.

With that said, the stock deck is only about .375" thick, so you are going to cut off about 18% of the deck to get the higher compression. This is not a good idea if you plan on lots of boost or nitrous. Also, you need to be meticulous about checking PTV clearance. 0.0659 is a huge mill. I wouldnt do it.

 

ok i figured it out!....Thanks for the help ATOMIC

SO STOCK 243 HEADS ON A 5.3 99-06 with factory dish piston

57.25cc chamber is 9.8 to 1 milled .050
58.13cc chamber is 9.7 to 1 milled .044
59.03cc chamber is 9.6 to 1 milled .038
59.95cc chamber is 9.5 to 1 milled .031

I was expecting to gain more compression than that!

 

Careful using all that math, you might be deemed an idealistic bastard.

 

so without starting another thread and being terrible with math what would a 5.3 with 243s milled .030 and a .040 head gasket be at?

 

.040 crushed thickness head gasket?
Well .030 mill and a .013 less headgasket gives a total of .043
So you should be 9.7 to 1
cheaper just mill .044 off the heads than spend all that money on a set of thinner head gaskets

 

gotcha. whats a safe amount of milling before valve clearance or any other issues with our dish 5.3 pistons

 

depends on cam used

 

I heard that after when u get to 50 thousands u start having firring issues with the manifold..but not for sure

 

.040 mill works for sure with no intake fitment issues.Anything over .040 i would mill the intake side of the head for intake fitment.