Im getting ready to buy an rx8 soon. Im getting a compresson test on it before I purchase, There is a rotary specialist near where I am getting the car from, and he said he can do the compression test along with a pre purchase inspection. But he said his his Electric compression tester is down but he can use his mechanical tester. My question is will that mechanical one still give accurate compression results?

 

no you need a rotary specific comp test. you will get seven #s. comp for each rotor face and cranking rpm

 

By mechanical tester does he mean a regular compression tester? If so, it does kind of work but it won't be near as accurate as a rotary tester. It will only give you very rough numbers but what it will do is verify seals are working and will give you an idea of the condition of the engine.

Ideally, try to get a compression test done with the correct tool.

 

You can kinda-sorta make it work with a regular(as in, designed for piston engines), mechanical tester, but you do need a slow-motion camera along with an OBD2 reader which is capable of reading live data.

You would have to basically try to capture the "spikes" of pressure reading as you crank the engine, and read the cranking RPM with the live OBD2 data. Even then, that's not really ideally compared to the numbers you can get from an electronic, rotary-specific unit.

 

Do you have options? Are there other rotary shops or Mazda dealers around who could test it for you?

If not and mechanical is the best you can do, its better than nothing. Any car you buy in the area will need the same test. You just have to take the results with a grain of salt.