Milling for compression-How much?
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TECH Enthusiast
Joined: Nov 2007
Posts: 719
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From: Evans, Colorado
Milling for compression-How much? Okay i have a 391 sbc (bored and stroked 350) (3.82 stroke crank). From what everyone tells me i have about 9.7 to 1 (static) compression with my 64 cc heads. Here in colorado (locally) the highest octane on pump is 91. what is the highest (recommended) compression i can run with that on the street? I was thinking shooting for 11 to 1, not sure(?). Also how much to i have to get milled to get this compression and what gasket do i use?? thanks guys
I ran an all iron 357 with 11:1 and 8.4 dynamic with 89 octane and 34 degrees total timing.
I later swapped cams and got 8.5 dcr that would not run with 89 octane.
As I said (to someone recently) get out the tools and cc everything, run some numbers.
You can get *** deep in bullshit taking other peoples word vs real world measuring tools.
I bought a set of 10:1 with xx cc head pistons from summit once, never checked, never ran right.
When I cc'd the domes I found out my engine had 11.4 scr.
Just my opinion, you have the engine, you need to do the work to figure it out. Do you really trust anyones guess here? If I threw out a number, would you shoot for that and trust me? I wouldn't.
EDIT: you say nothing about dynamic compression ratio. DCR is what determines what octane/max spark advance you can shoot for.
Yea you can run pump gas with 14:1 scr and a huge cam that'll get you 7:1 dcr but it's going to run like ****. Major ****.
I later swapped cams and got 8.5 dcr that would not run with 89 octane.
As I said (to someone recently) get out the tools and cc everything, run some numbers.
You can get *** deep in bullshit taking other peoples word vs real world measuring tools.
I bought a set of 10:1 with xx cc head pistons from summit once, never checked, never ran right.
When I cc'd the domes I found out my engine had 11.4 scr.
Just my opinion, you have the engine, you need to do the work to figure it out. Do you really trust anyones guess here? If I threw out a number, would you shoot for that and trust me? I wouldn't.
EDIT: you say nothing about dynamic compression ratio. DCR is what determines what octane/max spark advance you can shoot for.
Yea you can run pump gas with 14:1 scr and a huge cam that'll get you 7:1 dcr but it's going to run like ****. Major ****.
.006" per cc flat mill & generally .0075" per cc angle mill
At your elevation you can get away with running more compression, but think about where you will be driving the vehicle. That way you don't get yourself into trouble if you go down in elevation and are out on the road where your limited to pump gas. Like 9000th01ss said, check your head cc's, piston cc's (negative or positive volume), deck height measurement, and gasket volume. Take the time to do things right the first time!!!
At your elevation you can get away with running more compression, but think about where you will be driving the vehicle. That way you don't get yourself into trouble if you go down in elevation and are out on the road where your limited to pump gas. Like 9000th01ss said, check your head cc's, piston cc's (negative or positive volume), deck height measurement, and gasket volume. Take the time to do things right the first time!!!
