So did a compression test on my new (used) RX8 tonight. Just wanted to check and see what exactly these numbers mean.

All of the graphs showed compression at about 7 or so. However, I have no idea what hte RPM's are. The tester we had was analog, and doesn't list RPM's. Anyone know what the default RPM's would be with a stock battery? (you can click on the image below if you can't read it well enough)

 

https://www.rx8club.com/showthread.p...mpression+test

 

So then I can assume that standard RPM's on a stock RX8 are around 200RPM's?

I haven't seen that listed anywhere.

I'd read that thread already, but it's a single person posting the RPM's on their 8 while doing a compression test. I'm trying to find out if ~200 is normal or if there's a lot of variation.

 

its my understanding that you need 250rpm to do a good comp test and if you are below 7 it.s too low. I am not an expert though.
olddragger

 

I have attached the apprpriate pages of the Repair Manual.The really important thing here is that a compression test must be performed with a hot engine and valid recording of engine speed--otherwise you are wasting your time.

The earlier thread referred to where the owner was told that hot measurements were poor ,the proper response is to ask for the measurements--my guess is that they were not done .It is a real pain in the ***-oops I mean fingers to remove hot plugs and insert pressure tap.

As for knowlng the rpm--look at the chart--it is a requirement to interpret pressure reading.

 

I should say, we did the test ourselves. The engine was hot and I burned my fingers repeatedly trying to work them out of there.

The problem is that although we have a compression tester from the rotary club in our area, I didn't have any way to know what the RPM's were when the engine was turning over. The tach doesn't read anything while you're starting, or it was so low as to not register.

I was hoping that a stock RX8 would tend to turn over at approx. the same RPM's while running off the battery. Otherwise I need to get another program to read engine data while we do another compression test. My fingers would appreciate it if I didn't have to.

 

I suspect there is no "standard' turn speed now.Some cars are fitted with the updated starter motor which zips about 300rpm in my car.The original in my car struggled to make 200rpm.If you have the original starter in your crank speed would (probably) be less than 250 rpm.

 

rpms should be around 250