# What's the deal with Wankel engines?
**URL:** https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584
**Category:** Factual Questions
**Created:** [September 1, 2000, 2:24am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584 "2000-09-01T02:24:29Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Lizard](https://boards.straightdope.com/u/Lizard)
#### Post date: [September 1, 2000, 2:24am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/1 "2000-09-01T02:24:29Z")
I’m referring to those engines they used to put in some Mazda RX-7’s, back in the 80’s I think. I can’t possibly describe how these things looked or worked, but that’s not wshat this question is about, anyway. My question is: What were the advantages/disadvantages to Wankel engines? Why didn’t they catch on? Did they get better/worse gas milage thena conventional piston engines? Can you still get a Wankel engine in ANY vehicle today? Are they still used anywhere, for anything? Enquiring minds want to know!
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### Author:  [@Mr.Sheepshead](https://boards.straightdope.com/u/Mr.Sheepshead)
#### Post date: [September 1, 2000, 2:32am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/2 "2000-09-01T02:32:28Z")
Sadly, my auto knowledge is limited. However, I believe most Mazdas (the Japanese ones at least) still use Wenkel engines.
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### Author:  [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)
#### Post date: [September 1, 2000, 2:36am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/3 "2000-09-01T02:36:21Z")
> [@](#):
>
> \*Originally posted by Lizard \*
> Enquiring minds want to know!
Try [Encyclopedia Britannica](http://www.britannica.com/bcom/eb/article/idxref/0/0,5716,241608,00.html). There may not be as much pro-and-con discussion as you’re after, but it’s better than nothing.
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### Author:  [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)
#### Post date: [September 1, 2000, 3:29am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/4 "2000-09-01T03:29:36Z")
This is an excerpt from [http://www.freedom-motors.com/history.html](http://www.freedom-motors.com/history.html)
> [@](#):
>
> In general, the attributes of the Wankel rotary were outstanding, but in the automotive industry it was competing against the four-stroke piston engine with a 100 year history and hundreds of billions of dollars behind it. In addition, tests suggested that the Wankel rotary had poorer fuel consumption at lower power settings (at that time sealing was not as good as the piston engine at low speed).
>
> …
>
> The Wankel-type engine is less fuel efficient at very low power settings, which is where automobiles in the developed countries operate much of the time; i.e., 10% power at 60 MPH, 2% power at 20 MPH. In developing countries where engines used for transportation operate at the higher end of their power capability and where many two-stroke engines are used, the Freedom engine is far superior in fuel efficiency.
>
> Wankel-based engines have a remarkable record of reliability. Ingersol-Rand achieved over 40,000 hours without an overhaul. Rotary Power International (RPI) rotary engines (took over from John Deere) are guaranteed for a minimum of 10,000 hours, and most of the OMC engines produced in the mid-1970’s are still running today without an overhaul. Mazda racing engines operate an entire racing season without an overhaul while piston competitors are overhauled after each race.
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### Author:  [@bdgr](https://boards.straightdope.com/u/bdgr)
#### Post date: [September 1, 2000, 3:30am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/5 "2000-09-01T03:30:55Z")
> [@](#):
>
> \*Originally posted by Lizard \*
> \*\*I’m referring to those engines they used to put in some Mazda RX-7’s, back in the 80’s I think. I can’t possibly describe how these things looked or worked, but that’s not wshat this question is about, anyway. My question is: What were the advantages/disadvantages to Wankel engines? Why didn’t they catch on? Did they get better/worse gas milage thena conventional piston engines? Can you still get a Wankel engine in ANY vehicle today? Are they still used anywhere, for anything? Enquiring minds want to know! \*\*
Not an expert but, as I remember, they were all two strokes, which makes them bad emission wise(oil mixed with the gas). Suzuki made a motorcycle with one, and Norton supposedly did too, but it wasn’t imported to the states.
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### Author:  [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)
#### Post date: [September 1, 2000, 3:46am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/6 "2000-09-01T03:46:51Z")
The Wankel engine (often pronounced “Wonka” by wise-ass mechanics, like myself) I think only appeared in two popular cars in the US - the RX3, and the RX7.
The Wankel engine is known for smooth, high-revving power and a very compact and light powerplant. It’s also known for poor gas mileage, poor emissions, poor low-speed torque curve, and very poor reliability.
They didn’t catch on because they couldn’t compete with piston-engined cars in any category. Mazda really tried, and tried hard, but even the final year RX7 Turbo was not that great of a car relative to a Supra Turbo.
A shame really, since they were a neat concept.
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### Author:  [@yabob](https://boards.straightdope.com/u/yabob)
#### Post date: [September 1, 2000, 4:14am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/7 "2000-09-01T04:14:29Z")
Mazda has been showing a concept car, the RX-EVOLV, which has an updated version of the Rotary engine called the RENESIS. A new RX-7 based on the concept is scheduled to come out in 2002.
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### Author:  [@mangeorge](https://boards.straightdope.com/u/mangeorge)
#### Post date: [September 1, 2000, 4:25am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/8 "2000-09-01T04:25:20Z")
My ex-wife had a mid 80’s RX7. It was a little rocket, as long as you kept the revs up. Hell on clutches, though.
Peace,
mangeorge
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### Author:  [@yabob](https://boards.straightdope.com/u/yabob)
#### Post date: [September 1, 2000, 4:27am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/9 "2000-09-01T04:27:53Z")
Oh, and here’s a blurb on the RX-EVOLV:
[http://www.teg.net/CARS/rx-evolv.html](http://www.teg.net/CARS/rx-evolv.html)
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### Author:  [@brad\_d](https://boards.straightdope.com/u/brad_d)
#### Post date: [September 1, 2000, 4:46am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/10 "2000-09-01T04:46:44Z")
I don’t believe that Wankels are two-stroke. These descriptions seem to clearly indicate four “strokes” per cycle:
[http://www.freedom-motors.com/rotor.html](http://www.freedom-motors.com/rotor.html)
[http://www.monito.com/wankel/rce.html](http://www.monito.com/wankel/rce.html)
All four “strokes” are distinct, and take place in one turn of the funny triangular piece around its axis.
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### Author:  [@wolfman](https://boards.straightdope.com/u/wolfman)
#### Post date: [September 1, 2000, 5:00am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/11 "2000-09-01T05:00:31Z")
the biggest potential advantage of a rotary engine is that nothing ever has to stop. A traditional piston engine has pistons that to up, the stop and go down, eating up a fair amount of enegry starting and stopping the momentum.A rotary turns in only one direction so it doesn’t ever have to stop anything that is moving. The biggest drawback as I recall was getting both high compression and stability. The triangular center turns within the funny shaped outer casing. when the outer part is more bulbous there is more volume in the combustion chamber. The trapped air-gas mixture in the chamber turns to the less bulbous section(less volume) to compress the air enough for to ignite it. but the center triangle doesn’t rotate in place, but wobbles around the outercasing. If you make the outer casing dramatic enough to get high compression, the wobble gets more extreme, and keeping the engine in place becomes difficult.
But IIRC the RX-7 got a fair amount of horsepower out of only 1.3 liters, but the torque left something to be desired.
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### Author:  [@honkytonkwillie](https://boards.straightdope.com/u/honkytonkwillie)
#### Post date: [September 1, 2000, 7:11am UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/12 "2000-09-01T07:11:09Z")
> [@](#):
>
> \*Originally posted by bdgr \*
> \*\*Not an expert but, as I remember, they were all two strokes, which makes them bad emission wise(oil mixed with the gas). Suzuki made a motorcycle with one, and Norton supposedly did too, but it wasn’t imported to the states. \*\*
I’m pretty sure you’re thinking of two rotors instead of two strokes in the Mazda.
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### Author:  [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)
#### Post date: [September 1, 2000, 12:36pm UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/13 "2000-09-01T12:36:17Z")
I seem to remember it was theoretically very easy to increase the displacement of a Wankel engine, simply by “bolting on” another rotor unit. Of course it would have to fit in the engine bay of whatever vehicle you were modifying, and if it got too long there’d be drveshaft stability problems. Am I remembering correctly?
As far as efficiency goes, according to my cite the Wankel is less efficient at low revs. But it also says they’re very reliable.
A friend of mine had an old Mazda back in the mid-80s. He had some problems with the “thermal reactor”, but otherwise the car ran okay.
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### Author:  [@Centerline](https://boards.straightdope.com/u/Centerline)
#### Post date: [September 1, 2000, 1:09pm UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/14 "2000-09-01T13:09:35Z")
The wankel at first had sealing and lubrication problems (think large piston rings moving in two dimensions). Then material technology caught up but some of the bad press scared manufacturers away. The torque curve is a problem as mentioned. In general it is better suited to constant high rev usage similar to being in a jet aircraft, formula racing or cross country cruising, rather than start and stop traffic.
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### Author:  [@galen](https://boards.straightdope.com/u/galen)
#### Post date: [September 1, 2000, 3:07pm UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/15 "2000-09-01T15:07:49Z")
> [@](#):
>
> \*Originally posted by wolfman \*
> \*\*the biggest potential advantage of a rotary engine is that nothing ever has to stop. A traditional piston engine has pistons that to up, the stop and go down, eating up a fair amount of enegry starting and stopping the momentum. \*\*
I used to think this too, but now I’m not so sure. It seems to me that its possible that the counterbalances on the crankshaft work to cancel out the motion of the piston and rod. I’m not sure of this,though. We need the opinion of a mechanical engineer here.
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### Author:  [@sailor](https://boards.straightdope.com/u/sailor)
#### Post date: [September 1, 2000, 4:29pm UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/16 "2000-09-01T16:29:22Z")
> [@](#):
>
> the biggest potential advantage of a rotary engine is that nothing ever has to stop. A traditional piston engine has pistons that to up, the stop and go down, eating up a fair amount of enegry starting and stopping the momentum.A rotary turns in only one direction so it doesn’t ever have to stop anything that is moving.
This is mistaken. The only thing that takes energy is friction. The alternative motion of the pistons is like a pendulum: it stores energy during half of the cycle and it returns it during the other half.
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### Author:  [@L.Guardian](https://boards.straightdope.com/u/L.Guardian)
#### Post date: [September 1, 2000, 4:52pm UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/17 "2000-09-01T16:52:40Z")
Well, I’m not a mechanical engineer, but I did take physics. Anytime you have a mass that is at rest, it takes force to put it in motion and vice versa. The pistons in an engine come to rest at TDC and BDC (top dead center and bottom dead center). It is only for a fraction of a second, but they are stopped. To move them again takes force which “absorbs” work from the engine. The counter-balances aid in moving the pistons, just like the ignited fuel-air mixture. However, the fact they the pistons are mass that is being put in motion means that the engine _is_ having to work to move them. This is why racing engines use the lightest pistons that will stand the pressure.
> [@](#):
>
> By sailor:
> This is mistaken. The only thing that takes energy is friction. The alternative motion of the pistons is like a pendulum: it stores energy during half of the cycle and it returns it during the other half.
This is too simplified, and you are missing the fact that work is done to swing the pendulum back and forth. In the case of a pendulum, the work is done by the force of gravity. In the case of an internal combustion engine, the work is done by the momentum of the counter-balances and the ignition of the fuel. This means that the work done to move the pistons is not available to be transfered the output of the crankshaft.
We also all know that there is no such thing as a perpetual motion machine. Even if there were no friction a pendulum would not swing forever. Over time, it will swing slower and slower until it can not gain enough potential on the upswing to overcome gravity.
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### Author:  [@Centerline](https://boards.straightdope.com/u/Centerline)
#### Post date: [September 1, 2000, 6:10pm UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/18 "2000-09-01T18:10:06Z")
“We also all know that there is no such thing as a perpetual motion machine. Even if there were no friction [and no air resistance] a pendulum would not swing forever. Over time, it will swing slower and slower until it can not gain enough potential on the upswing to overcome gravity.”
Huh?..If I send an object out to space in a trajectory that let it miraculously miss all the planets and stars, and assuming no other friction, this object will travel forever, weaving in and out of all the planets’ and stars’ gravity fields! A pendulum will swing forever…there is no net work consumed nor generated.
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### Author:  [@L.Guardian](https://boards.straightdope.com/u/L.Guardian)
#### Post date: [September 1, 2000, 7:02pm UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/19 "2000-09-01T19:02:54Z")
> [@](#):
>
> \*Originally posted by Centerline \*
> \*\*“We also all know that there is no such thing as a perpetual motion machine. Even if there were no friction [and no air resistance] a pendulum would not swing forever. Over time, it will swing slower and slower until it can not gain enough potential on the upswing to overcome gravity.”
>
> Huh?..If I send an object out to space in a trajectory that let it miraculously miss all the planets and stars, and assuming no other friction, this object will travel forever, weaving in and out of all the planets’ and stars’ gravity fields! A pendulum will swing forever…there is no net work consumed nor generated. \*\*
So you are saying that perpetual motion machines do indeed exist? COOL!! And I always believed my physics teacher when he said they don’t. Boy, was he an idiot! (any cites?)
BTW, it’s not fair to add words to someone’s statement when quoting them. Yes, I did mean no air resistance, but I did not say it. Please, in the future, do not edit my words. I will admit that I should remove the “no friction” part, simply because we are dealing with a real world application here, and there is no such thing as “no friction” in an engine.
In your example above, however, your object traveling through space will slow each time it passes through a gravitational field. Eventually it will slow to the point that the next gravitational field it passes by will capture it, and it will enter an orbit in that field. Eventually, it will even slow to the point that it will fall in to the gravity well and crash.
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### Author:  [@Punoqllads](https://boards.straightdope.com/u/Punoqllads)
#### Post date: [September 1, 2000, 7:07pm UTC](https://boards.straightdope.com/t/whats-the-deal-with-wankel-engines/31584/20 "2000-09-01T19:07:29Z")
> [@](#):
>
> \*Originally posted by wolfman \*
> the biggest potential advantage of a rotary engine is that nothing ever has to stop
While rotary engines technically don’t stop, in any one direction perpendicular to its axis of rotation, it’s stopping just as much as a piston stops. Essentially, it’s trading off linear inertia for rotational inertia, so it’s not really a win from that aspect.
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