I called racing beat to get sme info on some products with my mazda6, and we got to talking about the 8, wince they are spending most of there resources right now tuning your car. One of the RB folks mentioned that there may be a problem with carbon building up on the exhaust ports?, which could be why some people are experiencing lower MPG than they should along with potential performance degradation. Since these guys are pretty plugged into mazda and the rotary scene, I take what they say more seriously than most things I read on the internet. I wanted to post this and see if anyone knew what I was taking about.

Have you guys heard about this carbon buildup thing?

 

That is the reason they didn't go to side exhaust ports years ago. I doubt it would build up that much in less than a year. The current engine uses less oil, so Mazda figured it would not build up.

Good theory, but I would hope they prove it first by disassembly/inspection before starting to talk about it.

 

Isn't it part of the reason as to why the rotary likes to be rev'ved up to redline? Helps clear the ports by getting a full burn.

 

They have improved it in the new Renisis engine but that is why we were (or atleast I was) told at the dealership to rev the engine to 3,500 rpms before shutting it off. I have noticed any decrease in mpg in fact mine has steadily been increasing. I also used gas in Idaho which is not oxygenated in the winter like our gas in Washington and it appears to be doing better but I will post my results when I refill the tank.

 

I have read about this regards to the new renesis engine.(I don't remember where. Maybe in one of the many car magazines that I have read thru.) They have suppose to take care of the problem. That's why the new RX-8 is out. Because the old RX-7 had this problem.

 

I believe Mazda has been researching the side port configuration since the 60's but had trouble with carbon build up. With recent technology they were able to eliminate side port carbon build up by using different coatings for the exhaust ports as well as redesigned side seals that keep the ports clean. These facts combined with less oil requirements are the key that made the Renesis come into production. I feel completely confident on Mazda's new design.

 

All I know is, I get a lot of carbon on my exhaust tips, and I try to rev it to redline at least once each trip. I did need an extra quart of oil at 2000 miles too. Hopefully just a cosmetic problem with cleaning the tips.....

 

Didn't the side port theory get thrown on the back burner because it wasn't the best way to go with carburation? Then they just didn't really figure that they needed to retouch upon it again when they switched to fuel injection because the former 13B porting was adequate?

 

FI rotaries go back pretty far especially with single rotor applications. As someone has said already, side ports got clogged pretty easily and the oil injection method didn't help out either. Today's renesis usues less oil and is injected differently with different rotor seals.

Renesis is still a baby as is the rotary in general. If it wasn't for that damn oil crisiss....