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My understanding is that everyone acknowledges that rotary engines are great, bt in comparison to piston based engines they have far shorter longevity.

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My '88 RX-7's engine went 120k miles before I decided to rebuild it and it still probably had a good 30k miles before it would have 'gone'.

This is completely normal through the 70s and 80s when these engines were popular. We didn't start getting million-miler cars until the Lexus LS400 came out.

The problem with the rotary is heat and the damage it does to other components. The RX-8's engine design was actually bad and doesn't adequately lubricate, but that gets 'fixed' in the last three model years.

The biggest reason that RX-7 owners have seal failures are often due to adding on too much power without adequately upgrading the fuel system. Keep in mind that Wankel engines are absurdly popular in the world of amateur aviation without any of the stigma.

They also have issues meeting emissions targets - both because of the basic design (there isn't the ability to actively control valve timing events), and also because they typically need some sort of lubrication for the combustion chamber. They are similar to two-stroke engines in these respects.

Running them at a pre-determined RPM constantly can resolve lack of VVT, but that limits their applications. New materials for apex seals being researched could alleviate their longevity issues too. But, I have a big soft spot for rotaries and would love to see them applied more :(

Isn't this how the range extender in the MX-30 works?

I guess the range-extender application is also less likely to suffer from the effects of lots of short trips.

Ohhhhh interesting, this would be a perfect fit for a range extender!

Whilst also being worse-performing?

Take a two-stroke Moster 185 engine: 25 HP at 7.800 RPM, for a 15kg package.

I'd be keen to understand how (if) this outperforms a typical two-stroke.

I think it's difficult to make a direct comparison because of the way the capacity of the engines is calculated. I know it's "fair" from one point of view, but it's not from another (depending on which team you support).

The only straight-ish comparison I can think of is the Suzuki RE5 vs the GT500, which are same-era motorbikes from the same manufacturer, with roughly the same capacity. The RE5 wins on horsepower (62 vs 44), but weighs about 50kg more.

My near-mint condition 2009 Mazda RX-8 never had a Wankel engine problem (over 100k miles). It would have easily lasted another 5 years without a doubt or hiccup.

Wankels are usually excluded from all engine comparisons, because it's a considered a different class...for piston engine marketing reasons.

I sold off my RX8 in 2018 because my fiancee and I moved to Seattle (passing emissions testing wasn't anything special). We needed the money and we had her car, which was more functional. I do miss it.

More antic-data: i worked with a guy whose brand new RX-8 needed two engines in the time we worked together. Granted, his was a 04 automatic, which is the worst combo. But still, Mazda didn't go out of their way to extend the engine warranties on the early RX-8s for no reason.

Did you happen to have an 08+ model with the updated engine and/or remove teh catalytic converter?

Yes, the model was 2009 automatic (updated my initial post for clarity). No, I did not remove the converter.

My RX-8 needed a new engine at 50k miles. As you likely know, if you start and stop an RX-8 engine without allowing it to warmup you risk flooding the engine.

In my case, I was taking a trip with my family and my RX-8 was blocking the driveway. We were running late for the flight, so I pulled it out, parked it back in the driveway, and let it idle there for 30 seconds knowing I'm not supposed to shut it down so quickly. But I had people waiting for me and what am I supposed to do, say "Sorry I own a strange car and I need to drive around the block for a bit to let it warm up!".

Of course that flooded the engine, but I didn't know until I got back from the trip. I followed all the instructions to de-flood the engine but it wasn't working for me so I had it towed to Mazda where they probably screwed it up further. It was there 2 weeks before they told me the engine needed to be replaced. They eventually had to fly an engineer from Japan to replace the engine since the dealer apparently had no one capable of dealing with rotaries. I think my car was at the dealer for a good 2 months. Thankfully all covered by warranty.

Long since mattering, but you could move them like this if you started it, rev'd it beyond 4k RPM, and then shut the motor off prior to it dropping below 4k. Basically, the idea was the rotors would force the fuel / oil mixture out of the crankcase and keep the spark plugs from fouling.

I loved my RX-8, but it was a pain in the rear. Switched to a WRX and got 50% better gas mileage, more power, more torque, and way more room. This of course bypassed the need to check / refill the oil every other fill up (aka, every 300-ish miles) all while trying desperately not to burn your hand.

I also experienced this flooding issue. Running it to a high rpm before shutoff to avoid the flooding, was a convenient workaround.

Why flooding the car (or frankly doing anything to my RX-8's engine) would require it to be replaced seems ridiculous. The casing of the engine is a solid piece of steel. Removing the ring gears and shaft (which you have to do for cleaning every 100k mi anyway), there's nothing to break.

Ofc, if you introduce the engine to some exotic combustion or get some foreign material in there, you could scar any part of the casing and that would brick the engine.

They're not great, at all. They have very few moving parts and they are very smooth because there are no reciprocating parts.

Other than that, they have emissions like 2-stroke engines because of the incomplete combustion and we have never been able to devise any kind of material to make the apex and side seals last anything like as long as piston rings.

Piston engines are a terrible way to power vehicles, but everything else we've tried is worse.

Wankel engines are great in one respect, power density. But they have terrible reliability and fuel efficiency.

Turbine engines also have great power density and terrible fuel efficiency, but they are very reliable.

Diesel engines are reliable and fuel efficient but heavy.

This one appears to have improved reliability and fuel efficiency over the Wankel without sacrificing power density.

Large turbines running at close to rated power actually have pretty good efficiency. Turbines are bad at scaling down to smaller sizes due to e.g. boundary layer friction, and also part load efficiency is poor. Recuperators help somewhat, though still not nearly as good as a piston engine.

LiquidPiston addressed both of those issues.

Mazda addressed both of those issues, Rotax addressed both of those issues, Norton addressed both of those issues, NSU addressed both of those issues, Comotor addressed both of those issues...

The issues remain fundamental, and largely unaddressed.

I understand this too, however, the technology might be worth revisiting with modern techniques, I understand the power output is 'smoother', which can reduce vibration, some applications might need that?

Nearly all engines need some level of vibration reduction if anything just to prevent it from damaging itself.

The problem with rotary engine is that its max power efficiency is at a very narrow rpm range and loses power at most other rpm ranges. This is due to the constant air intake inherent in the design. Piston engine has variable valve air intake to ensure optimal air oil mixture compression to deliver max power efficiency at a long range of rpm’s. That’s why rotary design is not popular for cars.

Mazda is reviving small single cylinder rotary engine design for HEV by running it at a constant speed with max power efficiency to charge the battery.

Some years past, a friend who worked for Mazda explained to me that the engines need to be driven for a bit because until they're warmed up fully there can be a lot of carbon buildup and it needs to be run some amount of time to get the carbon through. Once they're warmed up and running for a bit they're fine. Supposedly it's the short trips of only a few miles that can kill them over time.

Not sure if that's correct.

Yeah I talked to some race mechanics that said the mazda rotary engines had much better longevity if you really drove the piss out of them. They liked to rev high and hard, which would be basically consistent with that notion.

If we lived in a world of rotaries and BMW came out with the S85 we'd say that piston engines were emotive and fun but too unreliable for mainstream use. When we refer to rotary engines we mostly talk about two generations of one engine from one manufacturer used in sports cars that were designed before emissions targets changed.

The folks in the article seem to have figured some of the longevity problems out.

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