So i've done a search on compression numbers for the FD, however i didnt quite get an answer to what happens if you get varying numbers...

for example, this one FD that im considering buying got these compression numbers when warmed up:

the highest Rotor #2 was 7.2 and the lowest was 6.8.

Rotor #1 didn't do so well, the lowest it got was 5.8 and the highest was 6.1

This is on a original motor with 60,000 or so. From the search, they seem to be within tolarances, however, i am new to rotaries and would like your guys' imput.

thanks!

 

Below 6 kg/cm^3 = below Mazda's minimum compression specs. Assuming the comp test was performed correctly, that's not a very healthy motor. In fact, my motor is getting rebuilt right now -- front housing was just below 6.0.

 

disheartening to hear.. the person who owns this car claimed that it was running very strong... = (

 

It's a very sad but common thing for a seller to say. Some know better, some don't.

Dave

 

how many of these motors realy die form slightly low compression? Most die from broken apex seals. From what Ive been told equil numbers on all rotor faces is more important than high numbers. Just try to get it at a great price so if the worst happens you wont be out too bad.

 

Yes, the engine will probably run for several thousand miles yet. But there is damage somewhere in the front housing, as evidenced by the low compression. The car will have poor throttle response, less low end power, won't be able to handle high boost, and will likely get terrible fuel mileage, as compared to a healthy high compression motor.

 

sad to hear.. especially since clean FD's are so hard to find... this one was considering was very clean inside and out... this compression number, and the price, were the only real turn offs.. though the compression is too important to really overlook.