This engine used to be in the Mazda RX7. I wonder if it is still available in some new cars. If not, when was the last time it was used and why is it not used anymore?
It’s still used in the successor to the RX7, the RX8. I think that’s the only automotive use, though.
Uh, yeah, Mazda made a successor, called the RX-8
It’s a little odd that you know of one and not the other. Been watching The Fast and Furious I gather?
Maybe it’s just me, but I don’t very many of the the fast and the furious crowd knowing the rotary engine by the Wankel name.
I had an RX-8 for three years but sold it a few months ago. Lovely car, but too damn thirsty when you’re paying almost £1 a litre for petrol. 
The rotary engine, from what I read, had issues meeting emissions standards because the shape of the combustion chamber exposed more grease to the flame. The RX-8 was eventually released of course, but I assume that it was a good bit of a pain to get working up to standards and ultimately only a very small number of people would buy a car because it has a funny combustion chamber.
It’s used in the RX8.
The only real downside I know of is that the gas mileage SUCKS. Much worse than it should, given the weight and horsepower of the vehicle in question.
The RX8 has serious engine relaibility issues, but I don’t know if that’s really a problem with rotary designs in general.
I owned an RX-3 once upon a time. I was quite a bit younger and more irresponsible then and stupidly allowed the engine to run completely out of oil. I drove it until the engine seized up and stopped. The next day I came back, put in 5 quarts of oil, and it started right up and ran well. It did have seal damage and burned oil after that though. It was a remarkable engine with extremely high HP for the small weight and displacement. Only 3 moving parts in the engine itself. I wouldn’t call it a gas hog, but it was certainly not fuel efficient.
There is a second downside, and that is the engine is very dirty. The emission levels in a rotary are much higher than in a comparable Otto cycle engine.
IIRC HC and NO[sub]X[/sub] are especially high.
Yup, the RX8 is the only one. Almost bought one so I know a bit about it. Comes in two versions. A 4 port 197HP version with an auto tranny and a 6 port 240hp version which only comes with a stick.
It is a 2 rotor design and unlike the last gen RX7 is not turbocharged.
Reliablility is questionable. One thing I learned when researching was that when you shut it down, you have to hold it at 3000RPM for a few seconds or it won’t restart. This may have been fixed for 2008. It goes through a quart of oil every 1000 miles and fuel economy is not good especially considering the engine has an equivalent displacement of only 1300cc.
The RX8 is an eccentric vehicle with an eccentric engine. It did handle very very well though.
Anyone (especially Euro dopers) remember the NSU Ro80?
To the best of knowledge this is not true. I have driven them, and this is not a requirement. What you don’t want to do is have the battery go dead. I saw a Mazda instructor struggle to get one of his RX 8 running again after the computer lost it’s memory.
They use oil by design. Oil is injected into the lip seals to keep them working. The engine has a 7 qt oil capacity as a result.
Ran out of edit time.
A work colleague of mine who dabbles with remote control model aeroplanes informed me that there is a 5cc mini wankel engine. I found it here: OS Engines | Horizon Hobby RC Engines and Parts
Also, the seat belt tensioners in some VWs and most Benzs, uses a small wankel engine to pull the belts in during an accident.
Yes, although I have only ever seen one in my then hometown of Whitby, Yorkshire. Damned if I can remember who owned it but my dad knew them and being a fitter was very interested in the unusual engine design.
NSU still holds the licensing for rotary engines. I believe to this day you will find ‘NSU’ stamped on the Mazda Renesis engine.
I would like to correct this misconception. A vehicle’s fuel economy has very little directly to do with the displacement of its engine - a 5.7L Corvette gets the same EPA fuel economy rating as a 2.1l Honda S2000, and the Vette is a heavier, larger car to boot. There is no reason why a large engine cannot do the same work with the same amount of fuel as a small one. In the case of the rotary, this has to do with the compression ratio - two rotors == two combustion chambers, and 1300cc is pretty big for what is essentially a 2 cylinder engine. The low compression ratio in the rotors makes for inefficient combustion and increased emissions.
Without going into a lot of detail, my mechanic gave me the easy explanation for Rotary reliability: The engine revvs very high and has little torque, which translates into fewer reciprocating parts that none the less must move much more than an equivalent piston engine. Thus a rotary that’s gone for 200,000km has gone through the same amount of movement and stress as a piston engine with 400,000km. It came up while we were mulling over my friend’s RX-7, that I had convinced him to buy(That will teach him to ask me for car advice again).
That’s FAR from an exact scientific explanation and there’s a lot more involved, but it gives you a general idea. The RX-7 in particular also had a very advanced (for the time) sequential twin-turbocharger system, which added great deal of complexity to an already less-than-reliable engine.
I’m pretty sure the Mazda RX8 has a Wankel engine.
I got 'cher “wankel” right here! 
Again, to the best of my knowledge this is also not true. Do you have a cite for this?
Thinking off the top of my head, I can’t see how this could be true. The start up time for any internal combustion engine would exceed the time frame for deployment of the seat belt tensioners. We are talking <40 milliseconds for the tensioner to operate. Everyone I have ever seen is either pyrotechnic or mechanical (a big ass spring)
So once again, cite?
That is only because in order for Chevrolet to meet CAFE and other EPA fuel economy standards (and still be able to sell a ton of Corvettes), the 6th gear on the C5 and C6 Vette is almost absurdly low. Like an overdrive with overdrive so that at 65mph the engine is barely turning 1500RPM. That makes for good fuel economy so long as you stay at 65mph in top gear.
You’re not seriously trying to tell me that a 430HP 6.2l V8 has a ‘real world’ fuel economy that is better than a 2.2l 4 banger now are you?
Fuel economy is dependant on many things and one of the major factors is the displacement of the engine.
Not that I can add much at this point, but my basic understanding of why rotaries suffer in the reliability department is because you’re trying to maintain a tight seal in an irregular shape. Machining round parts is relatively easy - drills make nice round holes in engine blocks, and lathes make nice round pistons to fit inside them. Slap on a few cheap piston rings, and you have a nice setup that will withstand lots of abuse and even a little bit of wear/warping.
Rotary chambers are mostly oval, but not quite… it’s an oval with the sides tucked in a bit, sort of like an overinflated 8. You then have to get a triangle to maintain a constant seal inside that shape. The seals at each point of the triangle are called apex seals, and because of the extreme precision required to keep a seal with that bizarre shape, they wear out a lot. When rotaries fail, it’s not usually in a big kablooey, time to get a new car sort of way. They just start burning more and more oil until you can’t take it anymore and rebuild it. The trick to getting a rotary to last past 100,000 miles seems to be lots of proper maintenance and lots of luck.