Compression Question

[stinger222]

Since I have a crack in the #6 cyl wall in my 383 and it is all torn down, I thought I would install the vortec heads I have laying around in my garage. My current gm heads were milled to about 72cc when combined with my dished D-shape pistons gives me around 9:1 comp. The vortecs are 64cc, so my comp will bump up some. Will my comp be too high for marine use?

 

[John_S]

Re: Compression Question

You need to run the numbers through a compression calculator. Along with the bore, stroke, and cyl chamber size, you will need to know deck height, head gasket compression, and piston volume (+ or -). You will also need to consider you total advance timing and octane you plan to use. In general, it is good to be in the 9 to 9.5:1 range.

"http://www.kb-silvolite.com/calc.php?action=comp"

 

[Bondo]

Re: Compression Question

Ayuh,........

The Vortecs will take Timing Better, even with an elevated Comp. Ratio........
But,....
What you have going Against you is the Dished Pistons.......

With a .040 Quench the Votecs Really Shine......
Problem is,...
It takes D-dished pistons for the Quench factor.......

 

[stinger222]

Re: Compression Question

Ayuh,........

The Vortecs will take Timing Better, even with an elevated Comp. Ratio........
But,....
What you have going Against you is the Dished Pistons.......

With a .040 Quench the Votecs Really Shine......
Problem is,...
It takes D-dished pistons for the Quench factor.......

I do have D-dished pistons. I don't know how many -ccs they are though

 

[Bondo]

Re: Compression Question

Ayuh,.........

You can always Measure them.....

 

[John_S]

Re: Compression Question

mntrat is working on the same thing: http://forums.iboats.com/showthread.php?t=220630

I'd PM him. I am sure that there is allot of info you guys could exchange.

 

[stinger222]

Re: Compression Question

Yes I noticed that he is building basically the same motor. I'll PM him and exchange ideas with him. I just spoke with Dennis Moore by phone, and he said that as long as I have D-shaped quench pistons (he didn't ask the -ccs), keept the total timing around 30 deg, and run a 140 deg thermostat I should be ok with vortecs in a 383.