What prevented mazda engineers from increasing the offset of eccentric shaft for a longer "stroke"? larger moment arm = more torque right? what actualy governs this dimension? Not that it would be very feasible to say stroke a 12A 13B 20B considering the internal geometry of the rotor housings would have to be complety remachined (cutting toward the water cooling passages eek!) buuut... What actualy governs the geometry of the eccentric shaft? Is it a harmonics issue? Curiosity like this makes sitting in front of a computer designing circuit boards on a friday before a holiday really hard. Anyone have an idea on this one??

 

Good luck finding a 13A.

 

just guessing here ...
changing shaft profile for larger ... ahem ... "stroke" (using the term loosely and quite inaccurately) - i think it's called rotating axis or something - i would imagine that, yes, the housing would have to all be made taller and wider for an increased peritrochoid. the rotors would also have to be larger (pronounced, " even heavier") and Mazda perhaps figured that they were not going to be very efficient or responsive compared to the 10A, 12A, 13B and derivative designs. i belive they experimented with the very thing you mentioned with their 13A, 15A and 21A engines.

but don't take this as gospel ...

 

yeah the 21a was a 2.1l two rotor, but the oil crisis hit and they ditched it

 

because the reciprocating motion in piston engines is all lost once the piston reaches TDC or BDC. for the most efficient engine you want to create an engine with little to no reciprocating motion.

 

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you shoule listen to some of the conversations i have with my friends... that topic has been addressed a LOT--especially for the renesis engine.


there are some reports of maybe possibly a 15b engine being produced sometime in the future. with the side exhaust ports of the renesis engine, you'd have more air going in, but virtually teh same port size to get the exhaust out--which leads to backpressure and no-no stuff.

if the thing were made taller, you could get a much larger port, while decreasing port overlap, and improving power, reliability, emissions and gas milage all at the same time.

our whole take on the subject is:
rotaries are made to be turbocharged. period. even the high hp peripheral n/a's aren't as much fun to drive (to me) as a good turbocharged one.

give it more air and spin it slower. turbo engines (unless built with racing in mind) don't have any business spinning 10 or 11,000 rpm.

from an engineering/production standpoint, yea, weight is an issue, wear on the housings and apex seals, combustion sealing itself, blah blah blah.... it wouldn't be an easy job doing it, and i think mazda is trying its best to get a good balance of everything.

i didn't really touch on many of the downsides to doing this..i'll let the critics take care of that