what do 5.3 heads need to be milled to make 11:5 compression?
11-08-2008, 06:44 PM
#1
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what do 5.3 heads need to be milled to make 11:5 compression? I have some 5.3 heads and would like to see 11:5 compression how much milling will that require to reach that compression?
11-09-2008, 05:27 AM
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Lots of variables involved...
If nothing's been done to the heads (not ported), the 61cc 5.3 heads with a .040" gasket will land you right at 11.5 unmilled.
With a GM MLS gasket, you'd be 11.0-11.1, and would want to mill about .015" to get to 11.5.
Porting these heads and unshrouding larger valves usually enlarges the chamber size a couple cc, so they are typically more like 63cc in modded form. So you might need to mill .010-.015" or so to make up for that.
You should start this process using a compression calculator, and by choosing your head gaskets. Enter all the fixed data (bore,stroke, piston type, deck height, etc) into the calculator, then start playing with chamber size and gasket thickness variables until you arrive at your desired CR. Then (if your heads are not stock), have your chambers cc'd (actually measured), and then you'll know how much to mill to achieve your desired chamber size.
I had mine milled .025" to 59cc, and am also using a .040" gasket. With -1cc notch cut out of the pistons, I'm at 11.67:1.
If nothing's been done to the heads (not ported), the 61cc 5.3 heads with a .040" gasket will land you right at 11.5 unmilled.
With a GM MLS gasket, you'd be 11.0-11.1, and would want to mill about .015" to get to 11.5.
Porting these heads and unshrouding larger valves usually enlarges the chamber size a couple cc, so they are typically more like 63cc in modded form. So you might need to mill .010-.015" or so to make up for that.
You should start this process using a compression calculator, and by choosing your head gaskets. Enter all the fixed data (bore,stroke, piston type, deck height, etc) into the calculator, then start playing with chamber size and gasket thickness variables until you arrive at your desired CR. Then (if your heads are not stock), have your chambers cc'd (actually measured), and then you'll know how much to mill to achieve your desired chamber size.
I had mine milled .025" to 59cc, and am also using a .040" gasket. With -1cc notch cut out of the pistons, I'm at 11.67:1.
11-09-2008, 07:36 AM
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Lots of variables involved...
If nothing's been done to the heads (not ported), the 61cc 5.3 heads with a .040" gasket will land you right at 11.5 unmilled.
With a GM MLS gasket, you'd be 11.0-11.1, and would want to mill about .015" to get to 11.5.
Porting these heads and unshrouding larger valves usually enlarges the chamber size a couple cc, so they are typically more like 63cc in modded form. So you might need to mill .010-.015" or so to make up for that.
You should start this process using a compression calculator, and by choosing your head gaskets. Enter all the fixed data (bore,stroke, piston type, deck height, etc) into the calculator, then start playing with chamber size and gasket thickness variables until you arrive at your desired CR. Then (if your heads are not stock), have your chambers cc'd (actually measured), and then you'll know how much to mill to achieve your desired chamber size.
I had mine milled .025" to 59cc, and am also using a .040" gasket. With -1cc notch cut out of the pistons, I'm at 11.67:1.
If nothing's been done to the heads (not ported), the 61cc 5.3 heads with a .040" gasket will land you right at 11.5 unmilled.
With a GM MLS gasket, you'd be 11.0-11.1, and would want to mill about .015" to get to 11.5.
Porting these heads and unshrouding larger valves usually enlarges the chamber size a couple cc, so they are typically more like 63cc in modded form. So you might need to mill .010-.015" or so to make up for that.
You should start this process using a compression calculator, and by choosing your head gaskets. Enter all the fixed data (bore,stroke, piston type, deck height, etc) into the calculator, then start playing with chamber size and gasket thickness variables until you arrive at your desired CR. Then (if your heads are not stock), have your chambers cc'd (actually measured), and then you'll know how much to mill to achieve your desired chamber size.
I had mine milled .025" to 59cc, and am also using a .040" gasket. With -1cc notch cut out of the pistons, I'm at 11.67:1.
11-09-2008, 08:56 AM
#6
I'm running the Stage 2.5 5.3L heads, 63cc, unmilled
Gasket is a Cometic 0.040", Cam is a 230/236 612/600 111 installed straight up, Stock 346c.i. w/ 91k miles
I didn't flycut the pistons or mill heads and am running 11.17 SCR and 8.43 DCR
Gasket is a Cometic 0.040", Cam is a 230/236 612/600 111 installed straight up, Stock 346c.i. w/ 91k miles
I didn't flycut the pistons or mill heads and am running 11.17 SCR and 8.43 DCR
Last edited by White.Lightning; 11-09-2008 at 09:12 AM.
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11-09-2008, 02:11 PM
#9
Using a compression ratio calculator is the way to go. You can plug in different dynamic variables as in head gasket compressed thickness and combustion chamber size to get different numbers. Then, roughly .007 milled off of a head = 1cc of combustion chamber material removed.
