Why are most rotaries 654cc x #?
 

I know there was the 12A..., but how come there was never a larger displacement two rotor, or even three rotor? Is it something to do with the math, some inefficiency?

I was just curious, thanks for your time
Adam

there was a 13g (three rotor) in the second generation and then there was also a 20b (three rotor), but it wasnt in the 2nd gen. :D i personally think that there isnt too much of a need for a larger displacement rotary in a street car. i could see the 20b as being big enough for me.

paul

oh yeah, and there are a lot of people that stack a larger engine in a custom type job. mazda had the 787b 4-rotor le mans killer also.

Hey speaking of le mans. Isn't the 787B going to be in this year's? (next year's maybe?) I wanna watch it, how can I?

maybe mazda found that if they went any wider on the face of the rotor that they would run into ignition problems. we already have a difficult combustion chamber to ignite efficiently. dont need to make it worse. haha.

paul

i havent heard of the 787 being in the le mans. i think they retired that a long time ago. if they were gonna make another le mans move they would come up with something a little more technologically advanced than that car. they used pulleys and belts for the air horns. haha. . . and it still smoked everybody. gotta love mazda!!!

paul

http://www.howstuffworks.com/rotary-engine4.htm
from looking at the diagram i always thought that if the pockets on the face of each side of the rotor were larger, then compression would be waaaay too low for driveability, fuel consumption, and pollution. I'd like to know more too, if anyone has insight into this....

I think it's all about the thermal efficiency.

i think bigger does not mean better.
Something to do with how fast the flame for ignition can travel.
Maybe they can make it bigger but at lower top RPM limit... Basically does not run as fast, but powerful.

I think the same thing applies to piston, that is why trucks runs at slow rpm, while s2000 can go to 10000rpm...


reza

You can also increase displacement with larger housings and rotors. Compression is also determined by where the intake port is. This is why peripheral port rotaries cannot attain the compression of a side-port rotary. Part of the reason that the renesis is much more thermally efficient is because both the exhaust and intake ports are on the side housings, which means no overlap, higher compression, and retaining combustion gasses for a longer peroid of time.

Compression ratio is defined as the ratio between maximum chamber volume (volume at BDC) and minimum chanber volume (volume at TDC). Port location has absolutely nothing to do with it.

FWIW "Most rotaries" are 12As, not 13Bs... :D They haven't made 12As since 1985 but there are still more of 'em out there than 13Bs.

Oh quiet you 12a nazi!
:) Just kidding pj