compression tests

[KaiserDamz]

Hi, going to be looking at a few rx7\'s fd\'s soon and just wanting to check something.  Generally I have seen compression results given as things like 7.5,7.4,7.6 etc for each rotor.  Now sometimes I will see it just saying 95psi etc.  What is the better indicator of a better engine?

two cars im looking at have these results

Hello there just had Rex compression tested 95PSI in front rotor & 100PSI in rear rotor  engine turning for 10 seconds on each . I

and

 Front rotor 7.9,8.1, 8.1. Rear Rotor 8.2, 8.2, 8.5.

1st car is roughly 60,000 miles 96 year and second car is 48,000 miles 95 year, just wondering with two different styles of results how can you relate which is a better engine?

[m1tch]

You cannot use a normal compression tester on a rotary, the compression should be stated as such:

Front rotor 7.9,8.1, 8.1. Rear Rotor 8.2, 8.2, 8.5.

The piston compression tester can only test 1 compression, each rotor has 3 compressions, hence the 3 numbers. The values are important as well as how even they are, they should be close to each other.

Ask the owner of the car who gave you PSI readings to give you the proper mazda compression test readings, if the mazda readings are in bar then 95 psi is 6.5 and 100psi is 6.8.

The figues on the second car are very good, thats basically a fresh engine and has been looked after.

[KaiserDamz]

thank god you said that, i\'m picking up the second one tomorrow if it all looks ok. the first car was one i was looking at quite some time ago but guy went on holiday and came back and did a compression test.  The first car had a rebuild 9000 Miles ago so I know sometimes it needs running in till it gets good results but I think its best to play it safe and go with one with good results now.

[davehg]

Also find out what rpm it was done at as I must be 250 or you get the wrong results

[KaiserDamz]

it was done at 250rpm, car is in really good nick and low miles. sadly you can only see so much in pictures so will see for myself tomorrow.