The Mazda dealership did a compression test on my '90 non-turbo today and they said the readings varied from 7.8 to 8.1. Am I right in assuming they did this in kg/cm2? Also, if my conversions to lbs/in2 are correct, that would put it at ~ 110-115 lbs/in2....is this good?

 

Good nuf.

 

Those readings sohnd pretty healthy to me.

 

Thank guys! I appreciate the help.

 

115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment.

 

Heh a friends car was showing 70, scary huh

115 is perfect

 

accually, i thought 120 was perfect.... **** if 115 is perfect, then i guess my old motor that had 120/120 was a freak motor.

 

i'm a freak too, lol...when i got mine tested BOTH rotors were over 125psi! hehe

dual90s: looks like you've got a strong car

 

hehe, i got even 75's on both rotors and it still runs pretty good. just takes a while to get to redline.

175k miles

 

well, I meant 115 is perfect for an old motor.

 

Maybe you're engine is really just so close to carbon lock that your reading is great!

 

lol...wrong

it was tested 2 years ago...still daily driven today and strong as ever...

 

Just had a car checked today. Following figures are front rotor (3 specs) and then rear rotor. Help deciphering them appreciated!

Front rotor: 7.7 8.0 7.7
Rear rotor: 9.4 8.6 8.8
(when multiplied by 14 equals
Front rotor:107.8 112 107.8
Rear rotor: 131.6 120.4 123.2

on an engine with about 20k miles on it. Whaddya think, especially in the discrepancy between the front and rear rotor? Make any difference?

Thanks,
Tom Reynolds
Hereford, AZ

 

Anything over 100 is decent...over 110 is pretty damn good, over 120 is like new. Most rebuilds are *lucky* to exceed 115psi. Only a new housing, new seal motor will exceed 115psi. 125psi is basically brand new with less than 10k miles. After 50k miles compression starts dropping rapidly, and by 100k compression can be down near 90.

BTW< a 10-15psi differential between front and rear is normal, though not desireable. More than that and you start to worry...too much of a discrepancy will cause uneven idling and poor mileage.