Couple of questions about calculating compression ratio.

[Alfred1]

For those of you who have done this, did you use some kind of special tool like this ? I have a book about engine blueprinting that says you should take the compressed head gasket thickness into account when calculating the compression ratio (first photo below) but all of the formulas that I have seen for calculating an air-cooled VW's c/r (second photo) only take cylinder volume, deck clearance volume and combustion chamber volume into account and disregard the thickness of the compressed shim between the barrel and head. Is the thickness of this shim insignificant?

[woodman]

Good your looking this close at what you're doing. Porsche issued a tech bulletin recommending not using the head gasket. http://www.dolphinsci.com/techbull.html

Don't account for it in your measurments. Lap each cylinder to it's respective head to de glaze, if you've recently had head work done or had any material taken off the barrel.

[SteveStromberg]

http://www.aircooled.net/gnrlsite/resource/specgeninfo/calcs.htm

[Dave at Pelican Parts]

If you do use a head gasket of any kind, you can fold that into the deck height measurement pretty easily... Just add the thickness of the (compressed) gasket to the deck height. That will account for the gasket, though there will be a very small error induced because the ID of the gasket is usually a tiny bit smaller than the ID of the cylinder.

--DD