Rx8 Engine Builds | Understanding eccentric shaft end play / cooling factors and why it matters, especially here at altitude.
Mazda has a solid car with the Rx8, it handles well, excellent brakes and a roomy cabin. Since it has been 10 years since it was available at the dealership, people have been the reason for it still being a popular track / performance car.
With that comes the question of what to do when your motor is in need of a rebuild. What people miss when shopping for this here at altitude is where things can go wrong...quickly.
Overheating or running hot (230-242 degrees F) is going to reduce the life of your rotary engine. The problem is that here at altitude with our thin air the Mazda Rx8 engine and dash gauges is at a loss for real data.
The gauges in the Rx8 are at best a good-looking layout with a poor ability to give real information. Because the oil pressure fluxuates on the rotary, engineers decided that the oil pressure gauge should go to its desired spot and stay there. What that means is that it is at zero if no pressure and at a predetermined point when the engine is running. This makes the majority of drivers happy.
The same goes for the water temperature, it goes to its predetermined point and stays there....regardless of running hot. This water temperature gauge won't tell you that it is running too hot. I don't like coolant temps over 230 for long periods of time on the Rx8. For track day driving, I like it around 210 F.
Add to that a major issue of where the radiator is and the battery and intake plenum reducing the airflow after the cooling fans and things can get hot fast. Now, if you are missing the lower pan (as many that come into the shop are) the radiator / fans are being forced to work all the time. Result: A hot engine from everyday driving. This puts enormous strain on rotors and housings. Rotaries do not like to function at high temperatures for very long. I am a fan of moving the battery box and a performance air intake, this gives us room for hot air to escape vs. just making the radiator / fans work harder. The life of your engine depends on getting hot air out of there.
Ok, back to the original premise, building engines and end play of the e-shaft. If you are planning to run your rotary engine hard, and we expect you do (that is where the fun is). It is important that when you do have your engine rebuilt that everything mentioned above is addressed / modified.
We like to have an ample amount of room on end play. I like 3.5-4.5 thousands (of an inch) on the digital dial indicator. Ours goes to .0001 of an inch, that is 10 thousands of an inch. The right equipment matters for a proper engine build.
Our years of racing experience has shown us that end play matters and when it isn't enough, things can get tight. I know, I had this happen on a fresh build back in 1994, the engine wouldn't pull linear to redline, I could feel it slowing at peak power. Sure enough, I pulled the front off the motor, checked the spacer and when I put in a larger one, the engine freed up. We finished a well deserved 7th at the SCCA runoffs that weekend. Details matter.
Our altitude presents some tough hurdles if you are not aware of how to keep things cool and tolerances proper. Do it right, make it last.
