3 Rotor Engines
 

Here is a question, why has Mazda never tried for example a 3 rotor smaller displacement (1.3L maybe) engine. It would seem similar to me to making a small block V8 over a V6, where the V6 is a 2 rotor 1.3L design. I know that they did the Cosmo 3 rotor, but that never made it here. What really has stopped them from this, does it really not produce more power and just has more moving parts, is it hard to do the new port exhaust and intake in the middle rotor, are the housings not very scalable resulting in much more R&D?

i believe its a weight/power issue...that third rotor adds a lot of weight to the engine...i've heard about it used in the 90s cosmo and in various race applications (FC AWD rally car comes to mind)

I could see it add some more weight, but it is only .4L in displacement, doesn't seem like that would be too much especially compared with the potential power gain you might get from it. Remember this doesn't have to be a 20B.

I think it may be a fuel economy thing. The 1.3L Renesis already gets bad fuel economy. So adding some weight and more displacement would only make a bad thing worst. While I agree that a 3 rotor would be sweet, with the added torque and power, the economy would certainly be worse and approach that of a full size truck.

The suggestion was for a 1.3 L 3 rotor... Not that this would help. Efficiency wouldn't get any better, and may get worse since we are embracing the inefficient parts of one more rotor.

But I'd need to know how much more power it would generate per the loss of efficency to determine if this would be a good move.

Ok, this may be a hard concept, but what if there was no added displacement. I am not talking about a 2L 3 rotor, I am talking about a 1.3L 3 rotor, which would involve a different housing and rotor size etc than the 13B. Say we make the housings .43L each, and since we will have three of them that will add up to 1.3L total displacement, giving the same displacement. I am not quite sure how much more the engine would weigh, but I don't think it would weight that much more. Also as an alternative you could have one of the rotors turn off at below 30% throttle and that would give you better mileage than a 13B if you wanted it because since each of the rotors would be smaller it would have less displacement than the 13B yet it would still be smooth because you would have two rotors working if you wanted to go for good mileage.

Here's a few reasons:

Tooling costs would be astronomical (new housings, rotors, etc)
Ford accounting would never support it
Extensive investment in the current 1.3L that still has lots of opportunity for enhancement and improvement

What you are suggesting is a clean piece of paper. Very few companies would even dream of such an effort, much less pursue it. There is much more return on investment by utilizing existing technolgies.

There are smaller rotaries (10A, 12A) ... clearly MAZDA believes the 13B foundation is their bread and butter.

i would like to see a new 20B

Scoot in Japan actually built a custom 4 rotor from 12A engine parts (rotors, rotor housings, etc.). Absolute monster.

There has been a great many rumors that Mazda will look at going with more displacement for the rotary to increase power. The standard method to increase displacement is increasing rotor width - the 13b rotors are about 10mm wider than the 12a rotors. So, the iron housings all work, just new rotors, rotor housings, and eccentric shaft.

I would love to see Mazda do more with the 20b - that motor is just insane. They had a VERY tuned down version of it in the Cosmo - 400 horsepower is easy for a 20b. The biggest advantage of the 20b is TORQUE - lots and lots of it. I've heard stories from guys with high-horsepower 20b 3rd gens that said you can put your foot to the floor at 60mph in 5th gear and light up the rear tires. That's torque.

A 3-rotor design is also trickier to make. The eccentric shaft is multi-piece, and there's a thicker iron plate in the engine that is the intermediary, in a way. More time consuming to build, and more parts - that means more expense.

Anyhow, it's all just speculation. I would LOVE to see a 3-rotor design in a production car, but it's probably just not feasible. Who knows.

Dale

has anyone in all these years ever just created there own mazda based rotary engine from scratch? I mean we have the basic design, the parts seem rather simple, mazda did the hard part in the basic design research, so one would think one crazy rotor head would find some good cnc equipment and be able to do what your talking about. people build crazy custom piston engines all the time.

Hmmm, might want to ask RG or Wakeech on that custom building one. Madza managed to make the Cosmo e shaft, so I wouldn't see that much of a problem building more 3 rotor e shafts. Here is a question. I know that increasing displacement will increase the torque, but from the figures I have seen the 20B conversions have over 400lb-ft, which is more than double that of a two rotor, yet the new engine only has 1.5 times the displacement. Would having a 3 rotor smaller displacement engine be more torquey than a two rotor or equal displacement, or is the 20B torque difference only due to better tuning?

dcfc3s,

A good friend of mine just got back from Japan on Monday. Stopped in and shot the breeze with Scoot for nearly 4 hours. When he went to leave, Mr. Scoot asked him if he wanted a "little ride." Needless to say, the pic attached shows him coming back from his white knuckler! Lucky bastard!!


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A ride in an 3 rotor?

Anyways, I did have this nice dream where the RX7 was a 2L Renesis, and there was a MS stage 1 where they widened the rotors for 2.5L of displacement, and a stage 2 where they then used a screw type s/c on the stage one engine. If only...

Trying again... and that would be 4-rotor my friend:D

I've seen videos of that car, IMO the only beautiful part of it is the engine...

You've got to compare apples to apples. The 20B conversions are not using the 20B in anything close to the stock setup, they usually have a big single turbo, etc. The stock Cosmo 20B with the sequential twin setup similar to the FD made less than 300 hp....I don't know the torque but I can almost guarantee it was nowhere near 400 lb-ft!

jds

Ok, so then it was tuning differences. But then back to the question. Would a 3 rotor produce more torque than a two rotor of equal displacement?

Would a 3 rotor produce more torque than a two rotor of equal displacement?

My initial guesstimate would be YES, but I can't answer with any authority.

One thing I DO know is that two years ago during the Sevenstock Sunday Open House at Racing Beat, Big Jim (RB owner) said that one of the reasons why 3-rotors are not mass produced is the difficulty with balancing the assemblies at the factory. With a two-rotor engine, the rotors are oppositely opposed in the engine, hence very little counterweight is needed to balance the assembly. Three rotors take much more time to balance and require more counterweight for balancing. That plus the increased emissions difficulties I feel led Mazda to stick with the two-rotor design for mass production.

One more shot with the doors open!

nah. a 3 rotor of the same displacement would be a big step backwards. it would be longer, heavier, and i think the biggest knock against it would have to be the multipeice eccentric shaft (which is weaker).

20B's are great and everything, and Scoot's 4 rotor FD is next to god, but the bi-rotor has always been, and will continue to be as Dale said, Mazda's bread and butter production engine. even as a competition engine it's pretty good (just look at the Speed Source guys, and i can't wait to see Paul Yaw's car this summer!!).

I've seen the video of the 4 rotor, and I would have to say I would love the car, but the back of it looked horrible.

Ok, I accept that wakeech, but I've heard that it is extremely rare for an eccentric shaft to snap on a 3 rotor even though it may be weaker.

So basically not taking into account R&D costs and ease of development, it would be better for Mazda to produce a 2L Renesis by making the housing bigger, not just adding another rotor. Basically the 2 rotor 2L would be better than the 3 rotor 2L?

Hey Waaech

Another funny thing is that Ryan (my friend who rode in the Scoot car) said that Scoot was controlling the car with 2 Power FCs. He had two damn PFC Commanders in the cockpit. Pretty simple solution to engine management. I would have thought he'd be running a Motec or some other type of high resolution controller. I just thought some of you might find that interesting!

wow
that silver mazda is amazing to say the least

I want a hood like that

The Scoot car may not be super good looking, but I'm sure it's VERY aerodynamic - that car is totally built for top end. They also built a red FD with panels covering the rear tires - real odd looking, but again all about top speed. Had a ~700 horsepower 2-rotor (!) with full peripheral ports and a HUGE turbo. That thing was breathtaking!

The 20b was EXTREMELY under-tuned stock. Had smaller twin turbos than the 3rd gen, made about 280 horsepower at a relatively low boost. The intake/exhaust ports are huge, too, and the manifold flows a lot of air.

Dale

The problem with widening the current chambers is flame front travel. We already have the issue that some parts of the combustion chamber don't completely get burned since the flame front can't get there fast enough. By widening the rotors, you may get a power increase but it will not be an equal amount of gain compared to the amount of added displacement.

The 13B engines made alot more power than the 12A's but alot of it didn't necessarily have to do with displacement. The peripheral exhaust ports can only get so large. The 13B could get much larger exhaust ports than a 12A and therefore breathe better. 12A's have still gotten over 600 hp heavily turbocharged. A side exhaust such as the Renesis would take care of this. Now you can have the same size exhaust ports with smaller displacement. This is kind of like putting bigger ports on the same sized engine without changing the timing. You can really get some nice flow into the small chamber. The flame front also doesn't have as far to go. Personally I would like to see a 3 rotor version of the Renesis based on 12A dimensions. If we aren't talking about high boost levels then shaft flex isn't a problem. I think this would be a very nice nonturbo or positive displacement supercharged engine. 3 rotors just sound cool too!

For custom 3 rotor machining, contact Jeff Bruce in New Zealand. He builds 3 rotor parts (eccentric shafts, intermediate housings, etc...) from machined 2 rotor parts. He is very good. I need to go dig up his contact info.

Would just a simple change to 3 plugs per rotor or do a bit more timing change the flame travel ?

Mazda has experimented with 3 and 4 plugs per rotor, even on the side port pre-Renesis engines and found them to not work any better. The issue is really a distance problem. We also have a moving combustion chamber in relation to the plug locations. Timing still doesn't solve the distance issue.

The largest working rotary ever built was an experimental one that was about 7 feet tall or so. You've probably seen pictures of it. It was a 1 rotor and made 700 hp at an astonishing 100 rpm. The issue was that the combustion chamber was so large that the flame front could not travel across it effectively at any higher rpms. This was an extreme example but relevant never the less.

A product in development that I am very excited about could solve this issue. They are called smart plugs. They do not get fired by a distributer and are triggered through piezo electronics. They are not glow plugs though. Their flame front is huge since the patten is so intense. They send an explosion into the combustion chamber rather than a spark. Here's a link. Check this out. If I can get a hold of some somehow, I will. They are not available to the general public yet but have been used on rotaries. They can run anything from regular fuels to hydrogen to diesel fuels all on the same plugs!

http://www.smartplugs.com/about.htm

dcfc3s,

The silver Scoot car shown in the pics is the SAME as the red car you mentioned with the rear side skirts. This is what Scoot evolved the car into following his Japanese top speed efforts.

RG,
is my avatar the giant one you are talking about?

hydrogen you say? i wonder if Mazda is already experimenting with them in their hydrogen/hybrid rotary........

That's probably it. I hadn't seen that picture of it before.