Compression Ratio Calcs

[jgpainter2]

Just to confuse compression ratio issues more... What altitude is your base airport at? Mine (36U) is nearly 6,000'. This altitude (higher than many of you even CRUISE at) can allow and justify use of higher ratios. When racers come out here to the drags and Bonneville Salt Flats , they increase their compression ratios. Kind of like "normalizing" to make up for the thinner atmospheric pressure. When i perform a compression check during my annual on my 2.1, I have to account for the thinner air using a conversion, to get a representative reading.( Yes, a standard compression test - they have been relying on that for VW's since about the 1940's. Remember, you are looking for trends and differences). So, it makes sense to raise the compression ratio at higher altitudes of operation. After I raised mine from 7.2 : 1 to 8.6 : 1, the increased performance was short of incredible. Much higher RPM on climbout and WOT , on the order of near 200 RPM. I have the benefit of a local shop that builds VW engines for racing and dune buggies. They suggested the raise in compression ratio. Don't use the Sonex chart for calculating( i think too general and simplistic) - measure the cc's of your heads and do the calculations. Not really hard, as many resources online.
I am REALLY glad I put forth the extra effort. George. N1020X with 175 hrs.