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Final Verdict on Renesis
Submitted by Charles Wilson on Wednesday, May 2, 2007 - 9:59am

R&T had a comparo with 4 - 5 cars and the RX-8 won. Still, there were problems and recurrent ones. Is it time to total up the plusses and minuses on the "No Overlap Rotary"?

We still see the flooding problem, worse gas mileage than an RX-2 with blown seals. R&T complained of very low torque.

Has the Renesis engine development been a dead end compared with the recip or even with what research has shown the rotary could be doing right now?


Charles Wilson

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Final verdict on RENESIS
May 3, 2007 - 10:11pm
The comparison test was in Car and Driver, not Road & Track. But good grief, the RX-8 wins first place in the test, beating some heavy hitters, and we're trying to snatch defeat from the jaws of victory by emphasizing the problems that C/D harped on?

The Wankel rotary will never be able to produce a lot of low-speed torque. This is because of the fundamental geometry of the engine, as the rotor eccentricity dimension is roughly an order of magnitude less than the typical stroke dimension in a piston engine. Turbines don't produce a lot of low-speed torque either, for related reasons.

The rotary is a power and high rpm engine, not a torquer. Every engine design and configuration has its strengths and weaknesses. The key is to create the best compromise for your desired application. The frustration is that many companies will not consider the rotary for applications for which it would be well suited. The problems of the 1970s, much of which were due to excessive hype about the Wankel, continue to influence opinion about the engine today. What Mazda later called "lazy maintenance", leading to engine failures in the US, along with the NSU Ro80's major engine longevity problems in Europe, did not help matters.

You must keep in mind that C/D almost never gets anywhere near the EPA rated fuel economy figures for any vehicle it tests because of its testing regimen and driving styles. Keep your foot out of it and your mileage will be better. "Gee, I drove at 100 mph all the time and got lousy mileage. What a piece of crap!"

Considering that the conventional piston engine has well over a century of development under its belt compared to roughly 50 years for the Wankel, what Mazda has done with the RENESIS is little short of a miracle. You didn't ask for one, but I'll give you a broader view (and my opinions) anyway.

Except for the burst of money by licensees in the mid 1960s-early 1970s, the Wankel has never seen the size of the research and development effort that continues with the piston engine. For example, independent analysis using computational fluid dynamics (CFD) for Wankel combustion has been at a standstill for over a decade—and there never was a huge amount of it during its heyday from the mid-1980s to the early 1990s. It's hard to keep up when universities don't have much interest in continuing the basic research. Several academics seem to be under the impression that no one is building Wankels anymore, despite Mazda, OS/Graupner, Moller, UAV Engines Ltd (UEL), etc.

Also, Wankel research efforts at NASA's Lewis Research Center in Ohio dried up after Rotary Power International (RPI) acquired the old Curtiss-Wright rotary engine operation from John Deere in 1991. This work at Lewis dated back to the 1970s with Curtiss-Wright. RPI, not NASA, killed the research. (Lewis is now Glenn Research Center.)

And while on that topic, the Wankel has suffered from more than its share of charlatans who have drained money and hindered development and production plans. I can't vouch for the accuracy, but this seems to make sense: according to comments made to me off the record by someone who has been in contact with former employees, the people at the top at RPI in the early 1990s intended an eventual IPO (initial public offering) of stock that would enable them to cash out with loads of money—but would leave RPI foundering, as happened to a number of dot-coms that went down the same path. Developing the rotary was never in the bargain, as examining the legally required EDGAR reports for RPI will show. RPI was incredibly secretive, but the big secret seems to be that little new product development took place between 1991 and 2003, when the company went kaput.

As another example, it was alleged that those at the top milked Norton for money during the years of motorcycle production. That led directly to the end of the rotary motorcycles in 1993-1994 and to Mid-West and UEL taking over the Norton Wankel tooling for aviation use. If Norton had not pursued the aviation market in the mid-1980s, that engine would probably no longer be around in any form.

Examples exist of shortchanging rotary development due to financial problems or political reasons. Mazda required a bank bailout in the mid-1970s that hindered and nearly killed its rotary then. Ford came very close to killing rotary development at Mazda in the mid-1990s, and Mazda had a shoestring budget and only a handful of engineers for the new version.

All of these factors have handicapped the Wankel. Some of the specific RX-8 engine issues have other causes. For instance, Ford apparently required Mazda to specify 5W-20 oil in the US-spec RENESIS when 10W-40 is the spec in other markets. The thinner oil gives slightly better fuel economy, at least in piston engines, and Ford specifies it across the board in almost all its US vehicles now. Use of 5W-20 played a huge role, in my opinion, in the failures with the RX-8 engines here in the US, especially in hot areas. Australia has plenty of heat as well, but the RENESIS has had few if any failures there using thicker oils.

I'd say there is plenty of room left to wring more power out of the RENESIS design using turbo- or supercharging. There is also still a need for more combustion research on the rotary in general, especially the RENESIS configuration, using CFD and experimentation by independent researchers. Whatever computer simulations and combustion experiments Mazda and other manufacturers might be doing are being kept in-house and not published in technical papers available to the public. That leads to a vicious circle with the net result I mentioned before: no one considers the rotary for applications where it makes sense.

But I also believe that Mazda needs to start looking closely at stratified charge for fuel economy, especially since the recent US Supreme Court decision that basically says the EPA must regulate CO2 emissions (that is, require more fuel-efficient vehicles) or explain why CO2 emissions aren't a problem. Since Mazda sales have been brisk and even helping to prop up Ford, perhaps the company will be able to spend the money to make this change to the RENESIS design.

Certainly Curtiss-Wright had a handle on stratified-charge rotaries back in the 1970s, so there is little reason for Mazda not to use the technology, except for cost. This will be the new frontier. Fortunately, as with use of hydrogen as a fuel, the rotary is even better suited to stratified charge than is the piston engine.

The RENESIS is not "done". We can look forward to much more from it. A promising sign is use of the hydrogen version in the front-drive Premacy/Mazda 5, which implies that we will see variations in other vehicles besides sports cars, which have a limited market and will be targets of new fuel economy regulations. The next several years will be interesting for rotary buffs. Watch what Mazda does. By the way, also watch Moller and its arm Freedom Motors.
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There is no other car out the
May 6, 2007 - 2:31pm
There is no other car out there like the RX-8. It may have some quirks that need to be addressed but all cars are like that in some way or another. I have never in my life driven a car that feels as good as the RX-8. I have a 2004 and absolutely love the way it drives. (Although the gas mileage is not something I like.) But when it comes to real world driving over real roads, the RX-8 handles better than anything I have driven. It totally deserved to win the comparison against all those cars. And look at how they are doing in the in racing now? With a turbo this car would be a world class sports car like the old RX-7 used to be. But even as it is now it is really good!
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May 4, 2007 - 2:36am
I was gonna say that!
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final verdict
May 6, 2007 - 12:44pm
My sentiments exactly.

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