Hi everyone,

I don't post on rx8club that often but I wanted to mention a new spreadsheet I made to help understand compression results better when you don't have access to a Mazda compression tool. There was a thread recently on rx7club about some of the problems you run into when you check compression without the Mazda tool. Compression Testing - RX7Club.com One of the biggest concerns is the effect of cranking speed, but altitude affects the reading as well.

In that thread I suggested people use the compensation curves found in the service manuals to normalize your compression results for 250rpm cranking speed and sea level altitude. I checked a 2nd gen Rx-7, 3rd gen Rx-7, and Rx-8 manual and the correction curves are the same. I went ahead and made a Microsoft Excel tool to assist in the process. The tool is available here on Google Drive:

https://drive.google.com/file/d/0B_j...ew?usp=sharing

It uses the cranking speed (from some source besides the tachometer in the instrument panel), compression reading in psi, and altitude that can be easily looked up online (whatismyelevation.com). The compensation formula came from determining the linear slope of the curves in the service manual diagrams. This isn't as good as using a real Mazda compression tester but it's a step towards a more accurate understanding of engine health. A screenshot of the tool is below: