based8

"For the rx8:

readings above 115psi are excellent
readings between 105-115 are average
readings between 95 and 105 are weak
readings below 95 would generally fall within mazda's replacement guidelines, and such an engine would also have difficulty starting when hot, and perhaps have idle and stalling issues.

Technically the lower limit for compression on the rx8 is 96-97psi.

These values are at or near sea level and at or near 250 cranking rpm. For values measured higher than sea level, or values at lower cranking rpm, there is a correction chart to go by which tells you the lowest compression value that's acceptable because you will get lowered values at lower cranking rpm or higher altitudes."

hi i am a newbie to rx8's but not rotary's. i am going to look at a 04 rx8 with a reman engine that has 7k mi on it but i want to make sure it is in good shape and run a compression check. i found the above information which was quite helpful except it appears cranking speed is quite important with these cars.

Anyone have any idea what cranking speed a 04 rx8 with a fresh battery should be cranking at?

would looking for psi numbers around the above scaling be close with a 04 model ?

and lastly this is using the 3 bump method with the valve removed correct?


( im sure i probably posted this in the wrong section so here to make up for that is some *** for viewing pleasure )





Thanks

olddragger

iTrader: (3)

nice info concerning the compression values.
As you probably know a lot of variables have to be thought about when it comes to cranking rpm. But, in general with the updated starter ( not the oridginal 04 model) it is over 200 . at least the rx8s i have seen in ga have shown that.

based8

thanks for the reply, but i dont believe this has had a replaced starter. so with a starter cranking below 200 possibly ( guess im just going to have to gauge it looking at the tach when turning it over lol ) how should i adjust the values ?

Thanks

xexok

You need to get a proper compression test done, that will tell you the RPM as well as kpa/psi.

olddragger

iTrader: (3)

there is a chart available that will guide you for adjustments to the rpms--but like stated--if you dont have the tools for this important tests--you just need to get it done.

What are your vacuum readings?--that also can be somewhat of a guide to how well the engine is sealing.

Footman

iTrader: (2)

The acceptable range of compression @ 250 RPM as follows:

KPA:
830 standard
680 minimum
150 diff / chamber
100 diff / rotors

Kg F / cm^2:
8.5 standard
6.9 minimum
1.5 diff / chamber
1 diff / rotors

PSI:
120 standard
98.6 minimum
21.8 diff / chamber
14.5 diff / rotors

Remember values need to be normalized for 250 rpm.

muncheyboy

thanks footman!