hey guys.

Tryed searching and couldnt find anything.. i know im missing it because i found it here before, but looking for what compression numbers are good and what are bad. my engine has 147,000kms on orig. engine and it runs amazing with plenty of power thu out the whole band, but im curious as to what its compressions like so test time.. what are the numbers?

example

below 40 - needs rebuild

50-95 good

125 - new engine

you get the point..i hope

 

Mazda has set minimum compression pressure to be at 70psi. Good compression are readings anything above 100psi. Compression testing under 80psi is a sign of an engine requiring a rebuild soon. Compression should be even across all three rotor faces on both the front and rear rotors. It is more important to have all even compression numbers across the rotor faces versus one really high number on one face.

 

hmm well it turned out well for how many k's i have on the engine and how much abuse its seen.... 85 on rear rotor and 90 on front. 147,000 and the engines never been rebuilt. LOL and its seen quite a few turbos on it thx for the info tho!

 

no prob

 

what about on a 3rd gen which i have 105psi front and 105 psi back?

 

I believe it's the same except the minimum is 60psi instead of 70psi

 

Where did you come up with this ****?

The mazda specification for rotary compression has been minimum 85psi for all 2nd gens, correcting for cranking rpm and altitude. On the renesis/rx8 they raised this to 96psi.

Rotaries below 85psi will barely run and are a bitch to start hot, and rotaries in the 60s or 70's will no longer start at all without a roll start...and they won't idle and have zero low end power.

Please stop making things up.

 

I had a car with 60psi on both rotors and it started fine every time.

 

so is my engine good?

 

i would say that your engine is fairly worn. its still decent, yes, but the oil consumption may be higher(worn oil control seals) and gas mileage may be lower than that of an engine with better compression numbers and newer internal seals. you may find it difficult to start when the engine is hot or when the outside temps are high.

 

http://www.fc3spro.com/TECH/FAQ/compress.html

 

^thats funny because FSM says 85 PSI Minimum.

 

This is from the s4 FSM, the s5 and FD manuals are identical.

 

+1 I've always heard different things on the forums but every book that i have ever read was the same 85 psi. Then again, we don't always do exactly what the FSM says, and i am sure they put a "buffer" in their numbers. anything below 85 should be rebuilt. It will still run, but a rebuild before an apex failure is almost always cheaper and easier IMO.

 

So you've seen where I came up with this S@#$ and it's comes from a pretty reputable source so I wasn't making things up and sorry but your not allowed flaming until your post count reaches (10)

 

welll thats lame.. i did it when my engine was cold and w/o the pedal pressed at all... looks like ill be at it again.