Hi

How far offset are the eccentric shaft lobes in a 2, 3, and 4 rotor?
In my head I have this...
2 rotor - 180 degrees.
3 rotor - 120 degrees.
4 rotor - either 90 degrees, or 180 degrees in pairs (lobes for rotors 1 and 2 are 180 degrees offset from lobes 3 and 4).

 

You can time rotors in a rotary in whatever orientation you like, it's not a piston engine. Some people have even built eccentric shafts for 4 rotors with 2 rotor pairs hitting at the same time for a more torquey engine.

For the best balance and highest revving engine IMO a 4 rotor runs the smoothest with each rotor at 90 degrees.

Unless you have a very sophisticated machine shop you aren't going to be building them on your own though.

 

I'm asking about the offset Mazda used in their engines.

 

The standard Mazda 10A, 12A, 13B, 13B-RE, 13B-REW and 13B-MSP all have a standard 180 degree firing order.

The R26B 4 rotor which you can't buy or get parts for is a 90 degree firing order, the 20B 3 rotor I haven't seen anyone post specifics on the offset of the 3rd lobe however the back 2 rotors are standard 180 degree offset while the front appears to only be about a 10-20 degree or so offset from rotor 2. Most folks accept the rotor clocking that Mazda presented themselves with and never questioned it in regards to the 20B.

You would probably have to get your hands on a 20B e-shaft(good luck finding one, best I see now is repro custom ones for $7k+) and do the measurements yourself since I have never seen anyone post the info anywhere about the rotor firing order and degrees of offset for rotor 1.

Given the 3 rotor 20B is the only commercially available engine(and costs upwards of $20k these days for a rebuilt engine, new ones either don't exist or would cost twice that figure to try and source) I'm not sure this is a legitimate question. Building one from scratch is out of the realm of possibility for 99.99% of people, we still seem to get people who think these are modular engines you can simply stack together, those people annoy the rest of us because that's not how rotary engines work. It's the same as taking a V8 cast iron engine and wanting to turn it into a V12, it's possible, but it's not like you can just add a 4 cylinder to the back of the engine and make an F1 V12 motor, in fact it's easier to make one from nothing.

There is several shops that build custom 3,4, 6 and even higher rotor configuration engines but the people who come to this forum asking about specifics often times don't have the $100k in their bank account to back up their dreams, that includes a machine shop capable of doing the job. It requires specialty machines built for balancing rotating assemblies with rotor counterweights and precise lathes for machining the eccentrics.

I guess in short what I mean is just because you see half a dozen youtube videos presenting 3,4 and 6 rotor engines doesn't mean the vast majority of us will ever actually have one in our garage unless you devote a good chunk of your life to it or win the lottery. Anyone who is serious enough about this question would already have a 20B shaft in their hands to model off of, rather than relying on some questionable specs from someone on the internets. Or be drawing up their own blueprints based off of existing engine designs(by Mazda since their parts are easy enough to obtain rather than make yourself), again not relying on someone else to give questionable measurements. I rather doubt PPRE or DAW will step in here and give all their hard earned proprietary information regarding their own engine designs, additionally what works for them may not work for everyone who is a machinist anyways.

 

Running a big bang 4 rotor won't increase average torque, only peak impulse force. It's moronic as it means you can only put half the power through a clutch/gearbox as you could with an even fire engine of the same displacement/rotor count.

 

true, i suppose i explained it a bit wrong on my part.