Compression test /High altitude = lower readings
 

Hi, I am recently back to an Rx7 and read all the stuff about buying a used one and what to look for,etc...., well I bought it and decided to run a compression check on it.It bounced up to about 85 or in that range, but!!! I found out later that high altitudes affect compression readings. They will be lower. Is anyone familiar or have any info on that? I live in AZ at 7000 feet...so Im hoping my compression would be higher if this is true? Thanks

You would want a higher compression engine at altitude. The air is thinner and you can run higher boost/compression safely.

Foxed.ca - Rotary Compression Calculator

This might help you out. Found it on a thread somewhere in this forum but can't find the thread itself at the moment.

If the check was performed at low altitude, then the compression will be lower at high altitude. If the check was performed at high altitude, then the compression will be higher at low altitude.

You can use the calculator in the above post, or click on the RX-7 Manuals tab and use the graphs in Chapter 1 of the 1988 FSM.

I would recommend a turbocharged engine for high altitude. Non-turbo engines suck wind at high altitude.