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rotary/wankel engines... why not?

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How would you like to have 4stroke power with 2stroke price and reliability? I think it is possible, please, turn your attention to the Mazda RX series of cars. This small, simple, high reving engine is just what motocross needs! No valves! No Cam! No Reeds! No Frustration!

I think this would be a great solution to our "issue". But it has not been done yet to my knowlage. Why Is that?

A. Probably becase MX is sorta behind in tech. 2008 was the first of the electronicaly fuel injected MX bikes... a common technology we have had since the 80s.

Any other reasons? anyone?

I'm looking to start a SOLUTION thread, not a 2stroke vs 4stroke thread, so you strokists out there better straighten up your act and help contribute

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I'm sure others with more knowledge than me will chime in, but rotary engines have a few inherent disadvantages for dirtbike use:

- poor low RPM torque/power.

- powerful, yes, but power made by high RPM's not by large torque.

- poor reliability of the rotor seals.

- very poor fuel consumption

Let's assume that those can be satisfactorily overcome, the main issue is that you still don't really have an advantage over current reciprocating engines. What incentive is there to research, design and build a totally new type of engine for a relatively small market that is ony marginally, if it all, better than what you currently have.

BTW, with respect to your comparison to fuel injection, Wankel rotary engines are not "new tech" or even "high tech", they been around for years.

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Suzuki tried it over 35 years ago.

http://en.wikipedia.org/wiki/Suzuki_RE5

Arctic Cat also did a rotary in snowmobiles in the early 70's.

From what I've read these were all short lived because of -

  • Weight
  • Complexity
  • High fuel consumption
  • More heat created than a standards piston engine (not sure I grasp that one, unless it's just because these were in the day of air cooling)
  • Lack of low rpm power
  • Damage to seals caused when over rev'd

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These are all true, and thanks for giving me some answers.

With that said, I think rotating mass would be less, allowing a more nimble bike. Imo.

The heat is caused by the. Fact that one side is on the exhaust as the other is on the combustion, and the last is on intake. 2 hot sides to 1 cool side adds up after a while, the tricky part is cooling the inside. But my thoughts are this, if the Mazda RX8 can be a street worthy car (lowend torque is a must!) Then with modern technology, we can make a smaller powerful engine for bikes. With so few moving parts, I would think maintenance would be cheaper. The short stroke allows high engine speeds... however you are correct... low torque output... but look at the two stroke engine.

I think this would fix the "pollution problem" with 2smokes and the expensive maintenance with 4chokes.

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There used to be snowmobiles with rotary engines back in the day, but they suffered from most of the problems listed above. Obviously with today's technology most of those problems are much better (as the current rotary engines in the RX8 show), but I think there just hasn't been any incentive to try it again in a small vehicle.

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There were also emissions problems with the Mazdas, as I recall. But they were undeniably fast.

As a technician, my beef against them was that there was one symptom for every problem that they ever had; they wouldn't start. :thumbsup: Made troubleshooting a major PITA.

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As a technician, my beef against them was that there was one symptom for every problem that they ever had; they wouldn't start. :thumbsup: Made troubleshooting a major PITA.

:confused:

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The emissions problem is because they still ARE a 2-cycle engine and I believe my Mazda even had a metering pump that pumped a small amount of crankcase oil into the intake. Thats probably where the "oil comsumption problem" reputation came from. But I LOVED driving it! A definate seat-of-the-pants thrill. The older ones put any piston engine to shame comparing with what other "sports" cars were available.

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It's been done. Hercules Wankel GS.

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Look at the shape of that engine, with a bit of work on the frame and placement of the fuel tank etc, that thing could have such a low centre of gravity!

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A rotory engine is not a two stroke engine.. It has suck squish bang blow.. Only thins is because the "piston" is a rotor it rotates..

Second they do not rev high.. The reason for the "high" rev is because it rotates an essentric shaft thus for every one rev the shaft will be rotate three times.. So in all reality the tru rpms will be 1/3rd of what you see on your dash in an rx7-8 mazda

Next the reason for the exhaust temp being high is due to the fact that it's an open exhaust port design so as soon as the rotor clears the exhaust fresh flame is hitting the exhaust port and then a second ignition[sparkplug] ignites the remaining fuel right in the header thus raising the temp even higher.

Major issues with rotory engines was the forced induction models. The seals just could not handle the added power thus resuling in failure. How ever new materials reduce that and are imployed in the mx8 now.

as far as reduced wieght.. I don't see them getting them that much lighter then a modern 4 stroke if not it may even way more.. mainly because of needing to have a bigger case to acomodate the rotor and the weight of the rotor and counter shaft.

another problem is the fact that when a seal blows it pretty much ruins the plating of the housing. There are very very very very very very very few places in the world capable of plating them. Thus raising the price of repair.

I loved my rx7 but I don't think I want a wankle in my dirtbike.

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... It has suck squish bang blow..
I hate to break this to you, but so does a two-stroke. In truth a Wankel runs the cycle with no strokes because it's not a reciprocating engine.

The two-stroke reference is often incorrectly applied to rotaries because the tip seals require oil in the intake charge. The side seals can be pressure lubed and that oil could be kept from the combustion chamber, it just isn't always done.

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I hate to break this to you, but so does a two-stroke. In truth a Wankel runs the cycle with no strokes because it's not a reciprocating engine.

The two-stroke reference is often incorrectly applied to rotaries because the tip seals require oil in the intake charge. The side seals can be pressure lubed and that oil could be kept from the combustion chamber, it just isn't always done.

Then in the wording you put it's a no stroke or one long continus stroke since a circle could be seen as never ending. How ever due to the design of the rotor it has 4 distinct cumbustion intervals. air intake, compression, ignition, expulsion. another key factor is each side of the rotor only produces power in one full revolution or essentialy like a 4stroke that takes two full revolutions before power occurs vs the two stroke that fires and creates power each time the piston is tdc. Now you're going to say that so does the wankle Yes and No. mainly no becase you have to figure each side of the rotor is it's own combustion "piston" thus it can be consider a three cylinder design.

How ever it is in the same category as a 4stroke engine. Because each portion of the combustion process is separate from the others.. Before you go into well the combustion process is combined with the exhaust. You are correct but for only the last half of it.. Which for the most part modern 4stroke engines are also. The difference between two stroke and the wankle is that the intake is 100% in a different part of the engine thus no possibility of left over exhaust or escaped fuel/air during scavenging or intake.

Let it be known wankles due how ever expel unburnt fuel due to that fact of the open port. This is also why there is duel spark plugs to burn the fuel as it's exiting.

Humm I could be wrong but since I've built wankle engines Im pretty sure I'm right..

Ohh and gray you're right about the seals how ever the new genesis rotor I believe does not require oil injection for the seals. On another note people have been known to mix premix oil in their rx7s to help with this although marvel mystery oil is more used.

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