Why do rotory engines only have 1/2/3 rotors? Why not keep up with the piston and make hearty 12 rotors? Are rotors bigger? I think it would be awesome if mazda made a 12 rotor supercar. But... they haven't.

 

Mazda has raced 4 rotor engines, which is plenty of HP.

J-

 

Well, the more rotors the longer the E-shaft. This becomes a problem once you use more then 2 rotors. 3 and 4 rotor engines have been build right in the early days of the Wankel engine. But the engineers always struggled with the e-shaft. Due to the typical shape, and the fact that an E-shaft is mounted in the center of the engine/housings (where a cranckshaft basicly hangs under the block) it wasn't possible to build a long one (more then 2 rotors) in one piece, and the more pieces the more flex. Mazda's solution is to build a 2 piece shaft for 3 rotors and a 3 piece shaft for 4 rotors.
Mercedes Benz sollution in the seventies was to use a one piece shaft, but split the bearings of the centre housings. This was very difficult to construct if they wanted it to last, but it worked. They had a 350hp 4 rotor (non-turbo, mechanical injection) ready in the seventies, called the C111.
But since the amount of power that can be squeezed out of a 2 rotor (latest Mazda FD 280hp, the Renesis even does 230 without turbo!) there isn't that much need for larger engines. The Le Mans winning 787B had a 4 rotor (R26B) that is based on 13B specs, and developped about 700hp. That was non-turbo!
The three rotor 20B's are often making 400-500hp (twin turbo or single turbo conversion) and even more.
So a supercar powered by a 3 (or maybe a 4) rotor Renesis, maybe turbo'd, would blow all competition away, especially since the car can be build a lot more compact, and lighter.
However, there are always people willing to push it just a bit more, so Hurley engineering in the UK has build a 6-rotor!

 

after a certain number of rotors, u'll have multiple rotors firing at the same time which will gain no extra power.

 

Have you seen a 2 rotor engine in person? Let alone a 3 rotor?

 

Couldn't you offset them like with a piston engine? And even if they did fire at the same moment, wouldn't that just act like one bigger (wider) rotor, thus meaning more power? I really don't see why you couldn't build a 12 rotor engine from this point of view.
Of course, again, there's no reason to, and it wouldn't be the most reliable, since E-shaft flex would be huge, but there's no reason to say two rotors firing at the same time wouldn't make more power. Actually, I'm pretty sure that if you bolt two 13B's together you're gonna have more power then if you use one!

 

i am sure you could build a 12 rotor engine but you
are going to end up with a really long hood on the
car you put it in

matt

 

Ok...so a 12-chamber rotory is a little too much, but Hurley Engineering's 6-chamber would do well, or even a supercharged 4-chamber would give the same power, but less weight? Maybe mazda could offer different rotary sizes...

 

Basicy, if you'd want a really fast, really powerfull supercar, you'd be fine with a turbo'd 4 rotor, based on renesis components. We are talking power outputs in the real supercar-terms here. If the RX-8 makes about 230hp NA, a 4 rotor turbo'd one would easily reach 600-700hp. And it'd still be more suitable then a V12: it'll be lighter, shorter, lower, and overall: smaller.
But the point is: would a supercar named Mazda sell? Doubtfull, very doubtfull. The FD never did very well in Europe. People don't pay that kind of money for a Mazda. They go Porsche.

 

True, true, but it would be good to see some supercar rotory powered...ferrari, perhaps?