Compression ratio from compression test?

[My427stang]

Filling the cyl at BDC and TDC should work, but how to measure and pressurize if the plug is not at the top would take some thinking.

As far as using cranking compression, it wont work. Cranking compression is affected by valve timing and two different cams, or even the same cam at a different ICL will change cranking compression.

If you really wanted to know, I'd pull a head and measure, but my theory has always been...why take apart something that isnt broken

[TurboDiverArt]

Hi all,

I probably should have mentioned the reason for knowing this. I wanted to use it to get an idea of what type of fuel to use. When I got it I was using 116 because I was concerned about potential knocking. I have since dropped to 112. Car is running faster than I had hoped for when I bought it. Over the winter I took inventory of the car and realized the fuel pump was way too small for the application. The car had a Holley "blue" pump in it, which is basically a street pump. Car went 8's with it at 152 but I think it was running out of fuel at the top end. Always seemed to start lying over at the top end although the plugs looked good. Car never reacted to timing changes anywhere between 34 and 38 degrees. Definitely the wrong pump for the job, I've since upgraded so we will see if it goes any faster.

Art.

[Mr. Monte]

I have a 421 small block chevy and the reading on all the cylinders is 215. My compression is 14:1

[Gator]

If you look in the back section of the nhra rulebook..
the method is clearly spelled out.
or go to..
www.csgnetwork.com (search engine compression ratio)