Mods: I am cross posting from the 3rd gen section to spread the word. If this is not appropriate, please delete the thread.

Banzai Racing made a good thread in the 3rd gen section pointing out some of the problems you run into when you check compression without the Mazda tool. https://www.rx7club.com/3rd-generati...sting-1098715/ 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. I checked a 2nd gen Rx-7, 3rd gen Rx-7, and Rx-8 manual and the curve is the same. But it's not entirely obvious how to actually do that accurately. So I went ahead and made a Microsoft Excel tool to assist. 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.

 

Exactly the sort of effort/info that makes the forum valuable...so thanks.
Also the sort of effort that will sink below the waves if not stickied immediately.

Given that "Have you checked compression?" must be among the most commonly asked questions, let's keep this available.

 

You could put it in the FAQ

 

no but...misterstyx could do it though. in before the archive and stickie!! i'd like to say hi to maw.