Compression Test --> Opinions wanted
 

**This is a duplicated of a post I made on the 2nd gen forums, but due to lack of replies, I figured I would give this forum a shot. If that's a problem, feel free to delete this.



I'm about to buy an fc with low compression, so I found a car that had damage to take the engine from and swap into the one I'm buying.

The details of the engine (which I havent bought yet):

Front rotor: 7.7 kg/cm2, 7.6, 7.6

Rear rotor: 8.9 kg/cm2, 8.8, 8.8

*Compression was done following RETed's guide on a digital mazda compression tester.

The car is an 87 N/A with 54,000 miles. I have done searching/research on compression, but what would explain the disparity between the two rotors? I mean, the front is certainly good and the rear is awesome, but is there a problem with them being "significantly" different?

Thanks guys

Even though the ratings are different by slightly less than 10%, it is still enough despairity to raise skepticism. With that percent difference, the rotor might still be in working order now but there is no reassurance that it will maintain the marginally acceptable compression values that it has now. I personally do not use SI compression ratings but that sounds a little much.

SI compression ratings?

Marginally acceptable compression values? I thought they were both very decent.

Bump :P

These are the facts, straight from the long-time chief mechanic at the Northwest's best rotary dealership:

Anything over 7.0 is great, and readings in the 8's are superb and rarely seen in compression tests he has done.

My NA engine has readings from 7.0 - 7.9, and I'm very happy with it. You should be delighted with your readings... I would be! :)

Thank you sir.

Your response is far more encouraging than "marginally acceptable".

You're welcome.

I talked with that mechanic recently, and he commented that there is a lot of misinformation out there about compression readings.

See ya later.. :)