Why Don't Motorcycles Use Rotary Again?

nturtenwald · Dec 10, 2008

Since the classic 1976 Suzuki RE5 Rotary (check it out here: http://www.motorcyclemuseum.org/classics/bike.asp?id=39) dropped off the face of the Earth, no one has really talked about the use of the Wankel Rotary Engine in bikes much. Mazda has been struggling to help people see the efficiency of the Wankel Rotary engine and even lowered their standards by making the RX series more family-oriented. The RX-8 is now a 2+2 setup, lost it's turbochargers, and gained a bit of weight since the re-design. Quite the downgrade if you ask me or anyone else concerned with performance.

Rotary engines put an outrageously higher power/litre ratio than V-engines OR inline engines (Check out all the advantages here: http://en.wikipedia.org/wiki/Wankel_rotary)! Modern technology can keep the weight down and provides opportunities for the best efficiency. Rotary Engines can now adapt a fuel injection system that avoids the overly-complex carburetor systems of yester-year and advances in technology can stop all the reasons why the RE5 died out. There are independent companies that make project bikes for drag or track, but why not mass-produce them? Each Mazda rotary is approximately .7L (RX-7, RX-8 used two rotors for a 1.3L and 1.4L displacement, respectively) and put out approximately 120hp/rotary unit without tunes or upgrades!. A 1.4L can put out over 300hp that out-revs a Harley (well, a lawn mower can out-rev a Harley so that isn't much of an improvement)!

So the engine is light, puts out more power/Litre, easy to disassemble, and has been put in a bike before. Why not do it again? Maybe it can be done right this time around.

Countryboy · Dec 10, 2008

rotarys are the shit. My buddy has a turbo rx-7 and that son of a gun flys yet the engine is so small. We had it all apart and was showing me how a rotary works and all that good stuff. No wonder guys put them in dune buggies and what not.

See Steddy Win · Dec 10, 2008

I have said this before, but they are inefficient.

Plain and simple...Just because they are small displacement doesn't mean they are light either.

I believe the modern 13B is only like 35 lbs lighter than an LS1

nitrous36 · Dec 10, 2008

Yeah. Mazda won the 24 hours of Leman with one in 92 with the 787B. The pros to the motor is that it has less moving parts, which means less to go wrong and fail. But on the con side I hear they blow easier and typically have a shorter engine life, supposebly they wear quicker.

And if I remember right, the short life span is due to the tips of the rotors wearing away quicker than rings do on a piston.

Not claiming that this is correct. So if I am wrong on any of it please say so.

See Steddy Win · Dec 10, 2008

Apex seals...you were right, but it isn't the rotors, it is the apex seals...which is like a piston ring.

Only not really...fucking Doritos...:lol

nitrous36 · Dec 10, 2008

Yeah I knew it was some kind of seals, but just said the tip of the rotors for the lack of a better term.

Doritos:lol

nturtenwald · Dec 10, 2008

See Steddy Fail said:
I have said this before, but they are inefficient.

Plain and simple...Just because they are small displacement doesn't mean they are light either.

I believe the modern 13B is only like 35 lbs lighter than an LS1

Are you sure? Motorcycles will use quite a bit less wiring and material in addition to the weight reduction of the LS1.

The Aluminum Block LS1 weighs 434 lbs. (http://toy-jet.com/index2.html) while the Wankel Rotary only weighs 224 lbs (http://en.wikipedia.org/wiki/Mazda_Wankel_engine) but this number is based on the old generation model. [UPDATE: 2005 RX-8 Rotary engine weighs 344lbs sans fluid/tranny] You would not believe how hard it is to find the weight of the Rotary Engine itself! :cursing The only specs on it's weight are "LIGHT" and "SMALL". There are hundreds of musings about the total weight of the RX-7s and RX-8s (2800lbs+/- driver/useless passenger seats).

The Stock USDM (restricted) Wankel achieves a 196.2 BHP/Liter and grows from there. How much does your LS1 make?

nturtenwald · Dec 10, 2008

klutch_r said:
'Efficiency' and 'Rotary' should not be used in the same sentance. Sure, when you mention the volumetric displacement they sound like tiny, high-output engines, but they're not. That "1.3" liter Renesis gets about the same fuel economy as a Ford 5.0. They still burn an abnormally high amount of oil and eat through apex seals, even fifty years after the first mass-produced ones. I'll keep my I4, thanks.

I am talking about volumetric efficiency. The rotaries on bikes of yesteryear achieved approximately 35mpg (see original description of the Suzuki Rotary link). The technology has vastly improved and the numbers you're looking at are the gas mileage of the RX-7s and RX-8s. Keep in mind these cars weigh about 5x the weight of the bike and rider combined. And with the power the rotary engines put out, compare them to the Hayabusas and 1300cc superbikes.

Speaking of comparisons, how many miles can you put on your bike before you need to rebuild the engine? It's about the same time span that you'd see in a rotary. "But wait, if I don't push my bike hard, then I won't need to rebuild it" You can say the same thing about rotary engines. It just so happens that most Mazda RX owners buy sport's cars, not daily drivers. If you push your bike, you will blow the engine faster. If you push a rotary, the engine will blow faster.

And those apex seals go bad from high rpm use. Just like the piston rings on the inline series engines. If you keep the RPM down and regularly perform inspections and maintenance, you will avoid these problems.

And here's some old pictures of my 95' RX-7 next to my first bike. Memories. Especially of the bike's transmission that loved to slip out of first gear under hard acceleration. And who could forget getting pulled over and trying to convince an officer that there really were catalytic converters on the car.... And I'll never forget putting the car back to stock and having CHP inspect it. (They can't see inside the engine so they didn't know it was street-ported!)

nturtenwald · Dec 10, 2008

klutch_r said:
The RX7 is an awesome car, with an awesome engine - don't get me wrong, I love rotaries. But when compared with their piston-driven counterparts for most applications, the rotary tends to get the short end of the stick. I've done the comparisons, weight for weight, power for power, between the LS series V8's and the turbo powerplant from an '89 Turbo II for an RX build me and a friend did. Weight was within 20 pounds. Displacement didn't really matter power-wise - sure, the rotary was easily capable of 400-odd horsepower without too much work, but the V8 was already there, and with almost three times the torque, which matters much more for a car. Fuel efficiency was the same around town, and actually favoured the LS on the highway. Power was more easily extracted as well; as a dollar-figure comparison, the LS was at over 650 horspower after about $4 grand; the rotary would have taken nearly that much just to get it to 400 reliably.

Sounds like a cool swap! But you're talking about an 89 RX-7, not a 95 RX-7. Compare the Gixxers of yesteryear (like mine, 94) to modern (2007, or even +5 years to the 2001) A lot can happen in those years and technological improvements increase power and decrease weight.

And swapping in a built LS in place of a presumably stock TurboII is not necessarily comparable, I assume that replacement parts were top quality and there is no longer A/C or P/S. And I know for a fact that LS you put in was not an 89' LS for obvious reasons, so the improvement of technology stands as as evidence that as time progresses, engines weigh less, put out more power, and achieve higher efficiency in gas consumption.

Consider swapping the RX-8's "RENESIS" 13B-MSP engine into the Turbo II. Remove the 20 year-old components and replace with the bare minimum. You'll save a lot more than 20lbs and have a normally aspirated power improvement over the inferior first-turbo-generation design. The new MazdaSpeed setups will easily pull the RX-8's power above and beyond the 300 mark with equal torque boosts. But regarding price, the V8 is already there and costs a bit less. You win that round, sir! Don't forget to mention the custom-fabricated engine cradle that you need to fit that baby in there and the gas tank reconstruction (or probably fuel cell setup since you're going that far)

But we're getting a little

fftopic , aren't we? Back to Rotaries in Bikes!

SPL170db · Dec 10, 2008

nturtenwald said:
Since the classic 1976 Suzuki RE5 Rotary (check it out here: http://www.motorcyclemuseum.org/classics/bike.asp?id=39) dropped off the face of the Earth, no one has really talked about the use of the Wankel Rotary Engine in bikes much. Mazda has been struggling to help people see the efficiency of the Wankel Rotary engine and even lowered their standards by making the RX series more family-oriented. The RX-8 is now a 2+2 setup, lost it's turbochargers, and gained a bit of weight since the re-design. Quite the downgrade if you ask me or anyone else concerned with performance.

Rotary engines put an outrageously higher power/litre ratio than V-engines OR inline engines (Check out all the advantages here: http://en.wikipedia.org/wiki/Wankel_rotary)! Modern technology can keep the weight down and provides opportunities for the best efficiency. Rotary Engines can now adapt a fuel injection system that avoids the overly-complex carburetor systems of yester-year and advances in technology can stop all the reasons why the RE5 died out. There are independent companies that make project bikes for drag or track, but why not mass-produce them? Each Mazda rotary is approximately .7L (RX-7, RX-8 used two rotors for a 1.3L and 1.4L displacement, respectively) and put out approximately 120hp/rotary unit without tunes or upgrades!. A 1.4L can put out over 300hp that out-revs a Harley (well, a lawn mower can out-rev a Harley so that isn't much of an improvement)!

So the engine is light, puts out more power/Litre, easy to disassemble, and has been put in a bike before. Why not do it again? Maybe it can be done right this time around.

Norton made a rotary powered racebike, the NRV588, and it kicked some serious ass.

http://www.youtube.com/watch?v=VDngDlIuyIE

http://www.realclassic.co.uk/norton06120100.html

"Their presence set British racetracks alight, drawing huge crowds and Crighton's peak achievement was in 1994, when his Nortons sponsored by Duckhams Oils dominated the UK's premier Superbike championship. The winner that year was Ian Simpson, with team mate Phil Borley only missing second place by one point."

Sucram · Dec 10, 2008

Me and a mate pulled one of my old long engines (no carb, intake or exhaust)out with nothing but a pole, rope and our arms to lift it.

nturtenwald · Dec 10, 2008

Exactly what I'm talking about! Independent companies produce these bikes, such as Norton, for low-production runs but they aren't popular because of all the misconceptions about the rotary engines (review the entire post and I can disclaim any complaint you have to offer)! Look at the pictures of that bike, do you see that on the road everyday?

And you can't argue with the stat's on that bike:
# 588cc twin-rotor Wankel type engine.
# Fuel injected, direct spray into both bellmouths.
# Fully variable intake tract to peak maximum torque between 8000rpm and 11,000rpm.
# Electric water pump.
# Ducted fan air cooling for rotors.
# 'Fly-by-wire' throttle
# Power: 170bhp @ 11,500rpm
# Chassis: Twin spar aluminium, by Spondon
# Suspension: Ohlins USD forks, rear Ohlins long-stroke single-sided direct connection unit
# Brakes: AP Racing systems with radially mounted front calipers
# Wheels/tyres: Dymag 16.5-inch, Dunlop
# Dry weight: 130kg

Why are more companies not catching on or expanding on this technology!?!?

SPL170db · Dec 10, 2008

nturtenwald said:
Look at the pictures of that bike, do you see that on the road everyday?

I should hope not, that is a race bike and not in any way shape or form street legal

nturtenwald · Dec 10, 2008

SPL170db said:
I should hope not, that is a race bike and not in any way shape or form street legal

Blah blah blah. "Too high emissions, too fast, won't stop for police" Poppycock! ....Also, the article reads that if Norton (the company) wants to professionally race the bike, they need to sell at least 150 units annually. So touche, sir! Hopefully they will increase sales and we will see one on the street (and maybe be friends with the owner so we can beg a test-drive of the bike!)

i never sleep · Dec 10, 2008

It fucks up the handling.

Steve Hislop won the IOM TT on a Norton Rotary but he was a legend.

river rat · Dec 10, 2008

Prolly erelevant, but at the local dragstrip, I see them blow the seals on every other run, if not every. That's definately not a selling point...

Dream of Flight · Dec 10, 2008

I love the concept of rotary engines!

unk haven't really looked into all the logistics of it though...

SPL170db · Dec 10, 2008

nturtenwald said:
Blah blah blah. "Too high emissions, too fast, won't stop for police" Poppycock! ....Also, the article reads that if Norton (the company) wants to professionally race the bike, they need to sell at least 150 units annually. So touche, sir!

:scratch

Actually I meant it has 16.5 inch slick tires and no street going hardware (lights, signals etc). Weirdo

:scared

Hopefully they will increase sales and we will see one on the street (and maybe be friends with the owner so we can beg a test-drive of the bike!)

Don't hold your breath.

TheGeek · Dec 10, 2008

Rotory engines die really fast for one simple reason. Thermal expansion. The rotor grows with heat and wears the seals. When it's cooler, it leaks. Leaks cause deposits, which cause more wear. They basicly destory themselves.

That's the beautiful thing about reciprocal engines. The piston rings over lap to account for growth, and have elasticity (spring) to compensate for shrinkage. In a cold engine, without the rings installed, the piston will pretty much flop around. Heat those same parts up to operating temp and there is very little room to spare. There is just no way to keep a rotory engine sealed up when parts change size with heat.

nturtenwald · Dec 11, 2008

river rat said:
Prolly erelevant, but at the local dragstrip, I see them blow the seals on every other run, if not every. That's definately not a selling point...

Well they're not necessarily taking it easy through the gears, are they? That's a drag strip. Look at the inline engines on drag strips, how do they hold up? They're taken apart and inspected after each hard run. If they aren't taken apart, they're probably near-stock engines. The problem in this comparison is that there aren't any near-stock rotary bikes to compare to this because they're either fully built drag bikes or they're the bikes of yester-year that are never taken past 5k RPM

Why Don't Motorcycles Use Rotary Again?

nturtenwald

Countryboy

See Steddy Win

nitrous36

See Steddy Win

nitrous36

nturtenwald

nturtenwald

nturtenwald

SPL170db

Sucram

nturtenwald

SPL170db

nturtenwald

i never sleep

river rat

Dream of Flight

SPL170db

TheGeek

nturtenwald

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