new Mazda Renesis engine

[Rui]

I was just surfing the web and came accross an aritcle on the new Mazda Renesis engine that will power the new RX-8. This one sounds like the perfect auto conversion for the Cozy!! 250 HP at 8500 RPM (probably ~200 at a more conservative 6500). Also it seems that it is quite happy to go up to 10,000 RPM. 30% lighter than the old 13B. Physically smaller than the old engine!! Also it burns much leaner than the old, the only stat I could find about this was that it used 40% less fuel at idle than the old engine. This, of course is useless information since it won't be at idle much of the time, but it bodes well for higher revs as well.

 

The only thing that worries me somewhat is that they have increased the exhaust temps greatly so that the catalytic converter works better. It seems that this required a double wall exhaust (not too sure about this one site just had a passing remark about it).

 

So an engine with a published redline of 8500 RPM, limited to ~6500 means that it would be running at ~75% even when you have "full" throttle in an airplane application. Now all you have to do is add a turbo and you can have that power at all the altitudes you care to go.... Sounds really nice. Hopefully, in 4-5 years when I'll be making this decision there will be a reasonable supply of them around.

 

Is anybody currently looking more deeply into this new engine option?

[John Slade]

>Is anybody currently looking more deeply into this new engine option?

 

I agree. The new rotary sounds ideal. In a few years this might well be the engine of choice. Meanwhile, I'll run the 13B.

[macleodm3]

My biggest concern would be the exhaust temperatures... I remember watching the racing RX-7's catching on fire at every pit stop because the exhaust was so hot. The rotary exhaust pulses don't get cooled before exiting the engine as in piston engines. My neighbor has a new Harley and all the exhaust pipes have pretty covers so the blued chrome pipes are never seen. The weight savings of the rotary could allow for heat shielding from the exhaust... but who wants to put heat shields all around the back of a pusher airplane? I've been a long time fan of Mazda'a rotary performance cars and engines. One thing I've learned about Mazda is to not buy anything that they put out until its been out for two to three years. The last rotary they brought to the US was the twin turbo 13B which looked attractive with over 250 HP... until the turbos quit at 20k miles... consistently. Lets hope the new renesis has been tested more thoroughly and that the exhaust doesn't melt our planes... this engine may get popular with the execs at Ford and Mazda. I hope they sell tons of them so that they are easy to find! Lets see... 6 years from now when I might be ready for an engine... subaru WRX 227 hp, mazda renesis rotary, lycoming, continental, diesel... choices choices.

[John Slade]

Adding a turbo can be part of the solution to hot exhausts. Now all you have to deal with is a hot turbo

 

Also, the usage of the engine in a race car or street sports car is very different to what we'll be doing in an airplane. We'll be asking for lots of continuous power instead of sudden bursts and high revs. Those flying the 13B seem to have got around the heat and cooling issues. I understand that the 3rd gen twin turbo (but with the 2nd gen single stage turbo unit) is the best combination.

[Rui]

Interesting that you say that the old exhaust system was too hot. The descriptions of the Renesis say that they increased the exhaust temps because the old one was too cold which made the catalytic converter inefficient.....

 

Be nice to know actual temps on the new one...

[macleodm3]

Here is some info from a rotary enthusiast page, but I can't say its reliable: "The exhaust sytem requirements of a rotary engine are notably different from those of a four stroke engine. With rotary engines the exhaust gas temperature is very high - aproximatly 1,700-2,000 Degree's F at full throttle and high rpm,as compared to 1,100-1,400 Degree's F for a four stroke reciprocating engine. Also the unmuffled exhaust noise of a rotary is very loud"

 

Another good reason to slap on a 2nd gen turbo unit.

I don't know what temps Mazda is talking about with their new engine, but big companies always try to make a "problem" like high exhaust temps appear to be a solution "more effecient cat. conv." Their explanation does make sense though. I always thought it was funny how car companies said that the reason that the rear windows did not roll all the way down was to make the car "safer", although it is definately much cheaper too. Sorry about getting off the subject.

[marbleturtle]

Where did you see the info on the new engine?

[Rui]

for info about the engine just go to Google and do a search for Renesis (or Renisis, I forget the exact spelling). Good thing Mazda chose to invent a new word for it as the search will only bring up stuff related to the engine....

 

You'll mostly automotive magazine articles about it, but they had everything I said in my original post. If anybody has a better source (ie. from Mazda themselves) please post.

[Rui]

I was doing a little more reading about this engine on the internet and it seems that the double wall exhaust is to keep the exhaust at a higher temp until it gets to the catalytic converter. Not as I first assumed to protect the surrounding material from extra high temps.

 

Actully I'm not 100% percent sure either way. The articles are by car reviewers so they may get it wrong too...

[ekisbey]

I think that at 1700 degrees you're going to want the heat shield, regardless.