why 13bs 1.3 liters or 12as 1.2 liters what decides the size of the engine? what about custom made housings and rotors in a bigger size, this is just me talking out load so please no flames

 

12a is 1.1 liters

custom rotors ect means custom machine shop work
with enginering, balancing, ect.
starting from zero!

do you want to design, manufacture and build your own motor? way,way too much work and the cost must be enormous.

better to add an additional rotor/housing which they do;change the compression; add turbo/nitrous

see what everyone else has done on the rx7club for power gains

 

no i wasnt talking about doing it myself, that would be crazy, i was just thinking outloud i wanted to know why 1.3 liters has been the size of choice for so long

 

From what I've read, the 10A, 12A, and 13B, all have some interchangeable parts. The primary difference being the width of the rotors.

As far as the diameter(?) or the rotor goes, it has something to do with an amount of losing RPMs with larger rotors.

Since these engines make most of their power in the upper RPM range, a balance must be achieved to recieve the maximum gain.

I believe that physically larger diameter(?) rotors have a diminishing return for automobible, specifically sports car, applications.

 

just to add to what has already been said ...
i believe the main issue would be weight. horsepower is a function of RPM, and although larger (wider) rotors would mean better torque, the engine would be making less power (relative to the 60, 70 and 80 mm rotors that have been used to this point) ... the sheer weight would pose a problem.
even if the larger engine was modified to achieve the same RPM levels as say, a 13B, it would still be limited because of e-shaft flex based on rotating heavier rotors.

 

Mazda has experimented with alot os different sizes of engines and lots of combinations.

this site has some of the hardest to find info on all of the weirdest rotarys made http://cpwww.topcities.com/rotary/index.htm

 

The displacement of the engine is determined by subtracting the minimum combustion chamber volume from the maximum volume. This gives displacement for one combustion chamber. To determine maximum displacement for the engine you determine how often the engine fires in one 360 degree rotation of the crankshaft (eccentric shaft). In the case of a rotary it is 3 times per rotation. Total swept volume of the rotary (13B) in one complete rotation is 1308 cc. or 1.3 liters. Some less educated individuals argue that since this is only 3 out of 6 faces in the engine that displacement is actually 2.6 liters. Dead wrong. Piston engine displacement is calculated the same way. An 8 cylinder engine does not fire 8 times per crank rotation it fires 4! Therefore a 5.7 liter V-8 displacement is only figured based upon swept volume of 4 cylinders. If a 13B is 2.6 liters then the LS1 is 11.4 liters! I don't think so.

The main difference between the 10A, 12A, 13B family of engines is rotor width. Each one being roughly a half inch wider than the smaller version.

 

the whith is 10mm different in each engine. The 10A had 60mm wide rotors and rotor housings, the 12A was 70mm and the 13B was 80mm.

 

Right so far. No, it's the swept volume that's being calculated, so the number of times the engine fires per revolution isn't important. No, the rotor only completes 1/3 of a rotation per crankshaft revolution. No, that's not where the 2.6L idea comes from. A 13B sweeps 1308cc per revotution, just like a 1308cc piston engine. But with a rotary, twice as many of those sweeps is an intake stroke, so in theory it should inhale twice as much air, the same amount as a 2616cc piston engine, which is why they're more accurately compared to a 2.6L engine instead of a 1.3L one. In practice this doesn't quite happen, which is why most racing formulas use a 1.8 capacity equivalence factor (instead of 2.0) to class the 13B as a 2354cc (2.4L) engine. As I said above, it's the swept volume per revolution. An LS1 cylinder with a 99mm bore and 92mm stroke sweeps 708.2cc in one revolution, 8 x 708.2cc = 5665cc (5.7L).

 

Its just money.Im sure Mazda stuck with the 1.3L because they already have the tools ect. to make them. also, more displacement is not needed because the rotary is more efficient than pistons engines, so they can use the tiny 1.3l ( yes 1.3 not 2.6- who cares about airflow or how many times it fires, a piston engine is the volume of air between TDC and BDC x the # of cylinders whether its a 2 or 4 stroke).
If the rotors were bigger in the 13B and it was a 1.6L it would make more power and even more tourqe ( no replacement for displacement) and might not rev as high, but same goes for 2.0l and 5.7L piston engines ie honda s2000 revs to 9000 and has less torque than HP most larger engines rev to around 5-6000 but have more tourqe than HP. Rotories make lots of torque for their size : 12A- 100HP 106 ft.lbs/tq , 87 13B turbo- 182hp 183 ft.lbs/tq @ 3500 rpm 89 turbo- 200hp 196 ft.lbs/torque 91 cosmos- 20B 280 hp 296 ft.lbs/tq
gsl-se 135hp 133 ftlbs/tq ECT!! where did the rumor about rotories w/o tq come from anyway?Just admit it, rotories rock! LOL

 

If the rotory flows twice as much air , well that $#@%in awesome!

 

yes, but twice as much air means twice as much gas. the rotary's arent excatly fuel efficient.

 

If you want fuel efficient get a diesel.
Does anyone here care about fuel mileage?
rotarys should be classed in power range not size range because there are no 1.3L piston engines that can make 160 N/A stock in a production car.

 

i thought it was accepted that "twice the combustion volume multipled by the number of rotors" - AE 200

 

Each of the six rotor faces is part of a 654cc chamber, so you would get 2.6L with that formula. Counting all six rotor faces gives 3.9L, but it takes three rotations of the eccentric shaft to fire them all.

Piston engines only use half their displacement on a given rotation of the crankshaft, where a rotary uses all of its rated displacement (1.3L for a 13B).

There is no perfect answer about how rotary displacement relates to piston engine displacement, and there is even argument about the manner in which displacement should be measured/calculated. That means you really just have to learn how it works to get the understanding. There will be no "eureka moment" that makes the One True™ rotary to piston displacement relationship clear.

-Max