Compression Issue

Thought the cylinder chambers were 56cc on my head... they are 49 on the money. So my compression is now going to be 10.6:1, way too high for pump gas. So my question is... if I get a HG with a 50 crush, I can get down to around 9.9, which is doable.

Where can I source this gasket, what does it cost, and what's the highest compression I can run in a built 250 with a 4v carb and mikes head? Thanks so much, amigos

Hi, maybe you can enlarge the combustion chambers. Good luck

Sounds like you have all the pieces. Curious, did you calculate what the dynamic compression was going to be when you thought the chambers were 56?

I can't get more than a couple cc's out of the chambers.

DCR was around 7.4 to 1 I belive. May have been 7.8? Don't have my notes handy.

The Felpro head gasket is a .050 crush and is readily available at most part houses...around $30.

Using the Aluminum head you might be ok because it dissipates heat much more quickly than an iron head does. As an example on the 5.0 V8's they are able to use 1 point and more in static (higher) compression on pump gas than would be able to be used with the iron heads. I would be tempted to just try it or if you can find a good steel or copper shim head gasket you could stack them. Good luck

You might be OK if the DCR is still below 8.4. Couple that with what bubba said about the aluminum head, and I think you could be ok.

You need a ROL/Corteco gasket, compress ~.053". The new Felpro I have measures .046 uncompressed. They recently discontinued the ROL/Corteco gasket but I bet you can still find one. I have one but I want to hold on to it. The ROL part# is HG31060.

Crisis averted... double checked numbers... I'll be looking at a 9.9 - 10.05 SCR depending on who gives me the crush on a stock FelPro gasket. With my IVC at 65, this puts DCR right at 8.0. So I believe all is well and we are good, thanks for the help again guys. One step closer...

I actually have a ROL gasket. I'll bet you a shiny penny that I got it from rockauto. I would double check it but the thing is at the machineshop with my head.

You will be ok with 10.5 compression ratio since you have the aluminum head.
I would use the felpro gasket, cause I've heard of problems with the corteco.
Another plus you can get 93 octane fuel in your area of the country.
Make sure you test your A/F ratio. 14.5 cruise, 12.8-13.1 WOT. A lean mixture will promote detonation. Bill