The Mazda RX-9 won’t have a rotary engine

Hot off the heels of the Supra revitalization, the web is filled with the next possible RX Mazda sports car. Fanboys won’t be happy though, because what everyone wants is a ‘new’ ’93 RX-7. They want a gorgeous low slung lightweight body with two seats, a turbocharged rotary engine, 6-speed manual gearbox, locking differential and traditional Mazda chassis and suspension calibration. Sounds perfect, doesn’t it? It was. Unfortunately, the most important part of that formula to the fanboys is that turbocharged rotary engine.

The 3rd generation RX-7 is widely regarded as one of the best looking Japanese cars of all time. We all want the RX-9 to follow in these footsteps.

The rotary engine hasn’t been used in a production car since the RX-8 went out of production nearly 10 years ago and that one was garbage. A turbocharged rotary hasn’t been produced in almost 20 years as the FD was discontinued in Japan in 2002. A rotary engine in the form that we know it won’t be able to meet modern emissions standards, not by a long shot. There are a few deadly flaws in the Wankel design that hinder its ability to burn fuel cleanly. First is the basic shape of its combustion chamber and the rotor itself. Because the rotor comes to a point, it can only have one surface that touches the housing, the dreaded apex seal.

Because each rotor tip comes to a point, only one surface may be used to seal off the combustion chamber, the apex seal. This means preventing oil from getting into the combustion chamber is nearly impossible.

In a piston engine, the pistons use 3 seals against the cylinder walls called piston rings. The top ring is for sealing combustion pressure into the combustion chamber. The second ring is shaped to scrape the oil makes it up the piston skirt back down again. And the bottom ring is there to provide oil control. The rotary as mentioned earlier only gets one ‘ring’, and it better be holding combustion pressures in the chamber or this engine won’t be powering anything. Yes, Wankels use oil seals and such also, but nothing to specifically keep oil from the combustion chamber. In fact, rotaries use an oil injector to inject oil into the rotor housing for lubrication. Burning of this oil creates lots of nasty byproducts that must be filtered before they can leave the tailpipe. Catalytic converters can only deal with this burned oil for a short time before they become clogged up and stop working properly. A much more precisely controlled lubrication system would have to be devised and implemented before the rotary could be considered to power the RX-9.

The piston engine gets 3 rings to make sufficient sealing and keep oil from entering the combustion chamber.

The next hurdle is timing control, or lack thereof. One way modern piston engines broaden powerbands and meet emissions requirements is electronic control over when the intake valves open and close. Some OEMs even have control over valve lift, or how far and long valves stay open. The rotary uses no valves. Again, like a 2 stroke piston engine, there are ports milled into the side of the rotor housing. When the rotor passes over these ports it creates a vacuum to pull intake air in, or creates positive pressure to push exhaust gas out. A beautiful simplicity, but once the ports are milled into the housings, that’s where they stay. There’s currently no way of keeping ports open longer or shorter depending on engine speed or torque demand from the driver. This would be the equivalent of variable valve timing for a rotary.

On the Renesis engine used in the RX-8 Mazda moved the exhaust ports from the rotor housings to the side plates apparently in an attempt to improve tailpipe emissions. This reduces port overlap timing and improves hydrocarbon emissions.

40 comments

    1. Whoever did the rendering is clearly a fan of the FRZ/86 styling. An 86 with an LS would be a pretty good leap in that direction; should that be the next MotoIQ project car?

  1. Even though nowadays most car makers have no respect for the history behind the names of their cars, I really hope Mazda won’t call a car RX if there’s no rotary engine in it.
    Also, I hope I’m mistaken, but it seems very unlikely that Mazda will design a sports car powered by an ICE in the near future. Latest patents from the brand tend to show that it could be an EV with a rotary power generator like the MX-30.

    1. Lots of patents get filed that never make it to an actual physical model. That being said, I’d love nothing more than to be wrong.

    1. At that point, you could just put a Mazda-styled nose on a BRZ and call it a day. Then swap in a LS, and make Mike happy too (see above comment).

      I’d agree though, there really isn’t much to get excited about in the current Mazda engine lineup that would lend itself to a RX-9.

  2. Two things.

    First off, the NA 13Bs and even the Renesis closed off extra ports, affecting port timing in essentially the same way as 2-stage cam profiles, ala VTEC. This dates back to 1984.

    Secondly, the actual big efficiency/emissions thing isn’t burning oil, it’s inertia stratifying the intake charge in the combustion chamber leading to a mixture that varies from leaner than optimal towards one apex seal, to rich beyond combustion limits at the trailing apex. And then on the older peripheral exhaust engines this gets dumped straight out the exhaust port. On the Renesis, it gets recirculated… but moving the exhaust ports to the side means that heat flux is killing the temper on the side seal springs.

    This, by the way, is why so many “concepts” using rotaries are hydrogen fuelled – because that issue doesn’t apply when the fuel is roughly the same density as the air.

    I guess I just expected original content, even ignoring those points; I’ve seen articles like this about the RX-9 since the RX-Vision concept in 2015, and articles on how the rotary is dead back about 10 years before that. Yes, if Mazda is building a halo car there’s no indication in public as to what it would use as a powerplant, and yes, a lot of signs point to that no it wouldn’t be a rotary if they were. Since nothing in their lineup would work for a halo car, it would be interesting to see educated speculation as to what they could be working on would be interesting. Or heck, given it’s all the rage, talk about technology sharing agreements they have going on where they could be licensing powerplants with other manufacturers that could lead to a halo car powerplant. It’s not like Mazda is ignorant of what exists in the marketplace, nor of their own capabilities relative to larger companies.

    1. Thanks for the great insight Dan! I think you’re probably correct on Mazda resource sharing with another company to develop a drivetrain for the car, as much as I’d hate to see it be anything other than rotary powered.

      1. There’s rumors of Toyota and Mazda collaborating on a straight 6 using Mazda’s Skyactiv-X tech going around recently, so that’s one potential. In reality, who knows?

        Don’t get me wrong – I’m a rotary fan to an uncommon degree but the odds aren’t in favor barring some previously unknown wrinkle in tech.

  3. It’s always fun to day dream about the next “RX-9″… but I feel we only have two real choices if they keep everything in-house.

    A) It’ll be a taught up skyactive engine that produces in the neighborhood of 300hp, hopefully still allowing an option for a proper manual (not likely). Puts us in the $40-50k ballpark

    B) It will go the way of the NSX and all-in on the electric powertrain with crazy dual motors backed w/ some small combustion engine and push the price into $80-100k territory. Not a chance of stick shift here and sadly not a chance for most consumers.

    End of the day, I’m all for whatever comes out as long as it looks this good. Even if that means I’ll never own one, someone will, and we could all use this sight on our daily commute filled with drabs of crossovers and SUVs.

  4. I think automakers’ problems, particularly Japanese automakers, is that most people in product planning are not car people and are clueless. When possibly by mistake they make a wonderful car, the next version suffers from content creep and is a mess. That’s why Japanese makers lose their DNA and keep on making appliances. The NSX is a case in point. The new NSX should have used today’s technology with the DNA of the old car to make a lightweight 4-5 liter NA high revving engine with 500-550 hp with the performance target to exceed the Porsche GT3. Honda could have easily done this and the fans of the old car, including the adult kids who grew up dreaming of having an NSX that could now afford it would have bought them in droves. Instead, they built a car no one wanted alienating the fans of the car. Notice now that Japanese car fans are mostly into old cars?

    1. I think (I may be biased) that Mazda is doing better than most, but honestly given their resources I’d be surprised if they’re going for a halo car.

      But given as how I’m playing with early 80s RX-7s maybe I’m more accidentally proving your last point than anything.

    2. Good example. I felt very much the same way. Honda built another ‘daily drivable Super are instead of ‘fun, light, engaging, daily drivable super car. This was a huge failure as modern cars require so little compromise that most Super cars have become truly daily drivable.

    3. The new Corvette is realistically what the NSX should’ve been: parts-bin-engineered mid-engine supercar at attainable prices. What we got was a bloated gimmick-mobile like you say.

      1. I’ve never really thought about it that way, but you’re right. I think the upcoming z06 trim corvette is going to be really special.

          1. I can’t imagine GM going that route, but I could be totally wrong. I see an LT5 from the C7 ZR1 with maybe additional electrical power. As usual, I hope I’m wrong though.

        1. Bummer is most of the Japanese car companies have the ability to make these cars, just zero desire or internal drive. Nissan was going downhill then ze French finished them off. Now, I’m bummed when that’s all that’s left at the rental lot (hell, a Malibu is more appealing than an Altima). Honda built the Type R, then the design team watched Fast and the Furious 300 times and came up with that hideous bodywork. The NSX could’ve easily been a 4-500hp turbo J-series for under $100k, instead we get this ridiculously overpriced and overcomplicated douche-mobile. Toyota doesn’t build anything in-house, just provides some input to other manufacturers to build their cars.

          German cars were where it’s at, but content creep and bloat is turning them into gimmick-mobiles.

          Most of the fun cars are built by American companies these days.

          1. I agree with all of your sentiments Steve, but I must admit, I’m coming around to the CTR’s looks.

            Germans make amazing cars, but they’re all running to a center point of being the same car by different manufacturers. All the fast German stuff is powered by 4 liter TT V8 ‘hot vee’ engines with 8spd gearboxes, AWD and so much sound deadening you can’t even tell what’s thrusting you along at 200mph. Not to mention unless you’ve got $120k, you’re not getting any of those.

            American cars though….man. I’m proud right now. Sixth gen Camaro SS 1LE and ZL1 1LE are monsters, GT350 from Ford is amazing, C7 Z06/ZR1, C8 corvettes if you’re into DCTs. Everything dodge/SRT makes is gold in terms of fun. Everything can be had with a 6.4l 485hp naturally aspirated v8, or if that’s not enough opt for a 6.2l supercharged v8 making AT LEAST 707hp. Hard to argue with fun like that. Need a sedan – they got it, want a coupe? They got it…sort of. Need a jeep with 700hp? No problem. Oh, you have 3 kids and need 3 rows of seats and the ability to pull a boat but still want 485hp v8? Sure, here. And it’s all so very affordable (for a reason I understand) compared to the German stuff.

            That list alone is insane compared to what I came up with when a v6 Nissan Maxima made more horsepower than a v8 mustang GT and american cars were laughable. So much has changed.

  5. I did hear that Mazda was working on a skyactiv inline six-cylinder engine for a rear-drive layout.

    https://www.caranddriver.com/news/a27420382/mazda-rwd-platform-inline-six/

    Although the article suggests this would be more for a big sedan, this could be a sweet engine for an RX replacement. If, as the article states, it is based on the Skyactiv-X, this might result in a 3.0L with about 270 hp. While last I heard Mazda is still saying that Skyactiv-X will come to the US, this yet remains to be seen.

    1. If they did come in with an in-line 6 in the 300hp range, itd have to be significantly lighter and different than the current BMWs/Supra to make it really worthwhile. Especially keeping in mind the B58 and S55 in those cars make nearly 400hp.

  6. Fun fact, related to the picture caption about not seeing 2-strokes in anything but sub-350cc dirt bikes:

    You can go to your Evinrude dealer tomorrow morning and buy a 300HP E-TEC 2-stroke, 3.4L V6 with an ECU, triple throttle bodies, and a direct injection fuel system. They’re one of the cleanest burning outboards on the market, and still have the power to weight advantage that 2-strokes are known for. Not clean enough for the road most likely, but a world away from a carb’d dirt bike.
    They still have reed valves, and oil injection (100:1, expensive low-ash stuff), run on pump gas, and they are a badass engine to put on your boat. I have a 150HP E-TEC with 1700 hours on it, that’s been trouble free for the last 9 years since it was new.

    Also, I’m expecting Dave Coleman to suddenly materialize to defend the honor of the Mazda name. Where is that guy?

    1. 2 stroke is definitely still relevant in the marine world, but I’m not sure what their emissions are like compared to road cars. I’m sure the duty cycles and such are vastly different t given the use cases.

      I’d love Dave Coleman to pop up and smack me with an behind the scenes photo of a clean burning turbocharged rotary theyre currently developing! His writing has riveted me for almost 20 years now.

  7. I have owned 12 RX-7’s and one RX8 and need to have my bucket list fulfilled with another Mazda rotary engine car before I go.

    1. You’re a sucker for punishment. I’d love a nice FC turboII or FD. The RX8 felt like such a turd compared to the other cars of that vintage.

  8. I just had a thought that would solve much of the rotaries emissions problems that is possible with today’s technology. Direct injection with a staged stratified charge injection strategy. I wonder why Mazda has not tried this, it seems like a no brainer.

    1. Pratt and Whitney Canada have been patenting a bunch of rotary engine stuff the last 5 years; I’d have to dig into specifics if it was just heavy fuel or also spark ignition stuff. Also Curtiss Wright did stratified charge stuff back in the day. I’m just wondering if someone beat them to it and patented it.

    2. We know you have contacts…make some phone calls. But I’ve got to think with as common DI is these days Mazda has considered that. They already produce turbocharged DI engines for their SUVs.

  9. I have a driver’s license, which is how you know I’m old enough to remember when multiple magazines all showed different renderings of the next (now current) MX-5. None of them looked anything like what we actually got. A quick google search for “RX-9 concept” shows that the image at the top of this article is at least as old as 2018. I’d bet a set of Hoosiers that some kind of concept for the “next RX” gets sketched regularly by people who actually work for a Mazda styling studio, and they are better at not leaking said sketches than people who work in DC.

    I just hope that if they do build another RX-like car, they will make the interior have as much leg and head room as the ’79 RX-7.

  10. There’s almost certainly a new rotary in the works.

    “The technology development is under way [for a range extender hybrid],” said MX-30 program manager Tomiko Takeuchi.

    The MX-30 is Mazda’s first pure electric vehicle but will also spawn hybrid models, including at least one that uses a modern version of the rotary

    https://www.news.com.au/technology/innovation/motoring/motoring-news/legendary-mazda-technology-set-to-return-but-not-as-you-know-it/news-story/ddc2cb0d30a70dee36c86a550035abbe

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