Re: How to lower compression from 13.2 to pump gas

c.evans on September 17th 2010, 5:35 pm

IF, If, if, you decide to machine the top/crown of your current JE pistons, and put some dish in them to reduce compression ratio,,,,,be advised that for every 2.81 grams of weight removel, you have given yourself 1 cc of volume reduction. Restated; 2.81 gms. = 1 cc.

The reason I'm saying this is, because it is quicker to weigh a piston, than to "pour" for volume using a burret.

Uncle Charlie

Ed501 on September 18th 2010, 12:45 am

Thanks Charlie, that some useful info especially when you dont have a cc stuff but can borrow someones weightwatchers scale lol. Cool

res0rli9 on September 18th 2010, 2:38 am

weightwatchers sale

thats funny

dfree383 on September 18th 2010, 7:11 pm

Hogwash wrote:what about putting a thicker head gasket on?

that's the wrong thing to do with pump gas. Need quench to stave off detonation and keep flame travel right.

I may be in Montreal in November if you need some help.

bb429power on September 18th 2010, 7:19 pm

dfree383 wrote:
Hogwash wrote:what about putting a thicker head gasket on?
that's the wrong thing to do with pump gas. Need quench to stave off detonation and keep flame travel right.

I may be in Montreal in November if you need some help.

So would like 40 thou or 47 thou be an okay thickness for pump gas? That's what I have.

dfree383 on September 18th 2010, 7:53 pm

Low .040's is about as low as you can go safely. With the big bore in a 460 piston rock and contact with the heads becomes a problem any tighter.

rmcomprandy on September 18th 2010, 8:09 pm

Doug Rahn wrote:
Hogwash wrote:
Doug Rahn wrote:39cc dish will yield about 8.75 to 1.

oh wow still with those heads i have, they say its Combustion chamber volume 75cc? i though i would give me at least 10.1

Did I read your specs. wrong? I did the calculations based on 86.91cc. If the combustion chamber is 73cc then the C/R will be about 9.60 to 1 with a 39cc dish.

You were correct the first time ... the #1018 head gasket is 11.something cc's.

Doug Rahn on September 19th 2010, 5:57 am

rmcomprandy wrote:
Doug Rahn wrote:
Hogwash wrote:
Doug Rahn wrote:39cc dish will yield about 8.75 to 1.

oh wow still with those heads i have, they say its Combustion chamber volume 75cc? i though i would give me at least 10.1

Did I read your specs. wrong? I did the calculations based on 86.91cc. If the combustion chamber is 73cc then the C/R will be about 9.60 to 1 with a 39cc dish.

You were correct the first time ... the #1018 head gasket is 11.something cc's.

I see what you're saying Randy, he included gasket volume with his spec. When I did the first calculation on my spread sheet I added in another 10. something cc's to the mix. Spreadsheet I have will figure gasket volume, top ring land, etc.

I wish I knew how to post up Excel spreadsheets on here, so everybody could use them. I have some really good ones, compression ratio, piston speed, gear calculator, 4-link, and a few others.