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  1. #1
    The Cycle of Life Turbonium's Avatar
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    biking is like a rotor. (rx7)

    have you heird about the rx7 engine? its a rotor, it has no pistons that go up and down.


    well a bicycle is like a rotary engine, goes around and around. walking or running is like a piston engine up and down or back and forward, less efficiently. rotor

  2. #2
    Senior Member late's Avatar
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    Yeah,
    I had one of those a million years ago. It was in a Mazda sedan. Crappy handling, pathetic brakes, and an engine with a 5 speed that just wouldn't quit. It looked like a large, ugly, bright yellow potato.
    Unfortunately, you have the analogy backwards. Your legs are just like the
    piston/crankarm assembly. Pistons go up and down over a rotating crank. Your legs go up and down over a rotating crank.
    Old Man Maine

  3. #3
    The Red Lantern Rev.Chuck's Avatar
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    Just like a piston engine our legs have a power zone at middle of power stroke and a no power stroke at top and bottom center. This why Shimano tried Biopace.
    The rotary, however, is a great little motor. It is funny to see a carbed one sitting all alone in the engine compartment. Looks like you could just reach in and pull it out with your hands.
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    I heard that the rotary is really expensive to hook up becuase it has to run extremely rich. Aftermarket intakes, exhaust, all run the risk of making the engine run too lean, and therefore causing detonation, and in the rotary, detonation is fatal.

    Also the rotaries of the past burned oil like crazy.

    The new rx-8 is also a rotary...with undoubltely the same troubles. I think I'll stay away...

  5. #5
    Senior Member late's Avatar
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    Baloney,
    Phatman, I had a rotary sedan, my stepdad had a rotary station wagon.
    Neither burned oil; the bodies rusted away but the engines stayed strong. We didn't hot rod the engines. Back in the 50's and 60's poorly designed aftermarket hot rod parts destroyed a lot of engines. With experience, guys will learn to make hot rod parts, but it takes time. It's a gutsy little engine, I never felt a need for more power.
    Old Man Maine

  6. #6
    60mph in the 42 ring! Dave Stohler's Avatar
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    Don't forget, the rotary is an eccentric engine-it takes 2 revolutions of the shaft to get 1 rev of the rotor.

    FWIW, the "Wankel" rotary engine is a powerful, compact engine best suited to high-performance cars. Mazda (and previously, NSU) tried to use it in all kinds of vehicles that it wasn't suited for: luxury coupes, station wagons, even pickup trucks. Rotaries are not fuel-efficent, and never will be.
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  7. #7
    Senior Member Greg's Avatar
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    If a rotory is burning oil, there's big problems inside.

    These little motors are actually quite fastinating.

    Mazda uses a patent of the American designer, Wankel.

    Chevrolet has experimented with three rotor (as opposed to the usual two rotor) Wankels with extremely high horsepower output.

    As for the analogy, it works for me. Power in 360 degrees.

  8. #8
    Can't ride enough! Da Tinker's Avatar
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    The Wankels were great engines if you just allowed them to warm up before pushing hard. My mother (who has the soul of a race care driver) had one, which I installed a turbocharger on. It seems she couldn't beat out a buddy with a turbo Nissan Z. She drove it, equiped with Pirelli P7's until back trouble made it difficult to get in and out of.

    In the hands of an unenlightened driver (like my wife), who will just 'pop & go' in a cold cold car, a Wankel dies an early death. Pity.
    Happiness begins with facing life with a smile & a wink.

  9. #9
    Chi
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    Rides with Cows Chi's Avatar
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    I want a Wankel.

  10. #10
    The Cycle of Life Turbonium's Avatar
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    see the rotor motor didn't have as much time to develop as the piston engine. the piston engine had much much more time to develop and to fix the problems. if you were to give to rotary engine as much time as the piston engine then it would have better fuel consuption etc..

    as the analogy, a piston engine has to go down then stop completly and then acelerate back up, which creats stess. a rotary just has to turn and turn. in biking you are just turning and turning the crack. in running or walking you have to acelerate your foot forward to a stop and back. thats why in running you can't go too fast.

    the fastest rotary engine went 25000rpm and the only limitation to that speed was fuel suply.

    no rotor no motor.

  11. #11
    60mph in the 42 ring! Dave Stohler's Avatar
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    Years ago, when Mazda was racing an RX-7 in IMSA races here in the US, I had the chance to observe the mechanics in the paddock overhauling one of their race motors. From what the head mechanic told me, the actual motor was nearly bone-stock, having only had some machining to the edges of the ports. A huge turbo with a computerized wastegate was the only real difference between a stock RX-7 motor and this 600 hp engine.

    Oh, another advantage Wankel rotary motors have: they have only 1/4 the moving parts, and are very easy to overhaul once removed from the car. A decent mechanic can completely disassembe one in an hour, and be completely finished with an overhaul in one afternoon.
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  12. #12
    Footballus vita est iamlucky13's Avatar
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    I like rotaries, so I'll let the analogy stand on that basis.

    In WWII, a P47 pilot took a bunch of anti-aircraft fire and his (2100 hp rotary) engine starting sounding funny, so he turned and headed back across the Channel as fast as he could. He made it fine and on landing found two of his cylinders had 20 mm diameter holes in them. That plane was a beast.
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  13. #13
    Senior Member late's Avatar
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    The Jug (P47) was an amazing piece of hardware. I have read many stories; and I would bet a lot of them are true, of it's unbelievable toughness. While it had a rotary engine, it was a typical aircraft rotary design. The pistons were arranged in a circle around a crank. Quite different from the Wankel. One guy coming back damaged from a flight overflew American AA ahead of schedule. The full battery of AA opened up on him, ripping his plane stem to stern. Somehow, he got the plane down ; and as he was taxiing down the runway, the entire tail of the plane fell off. Someting I find even more remarkable was the the main *** of the FW190 was designed to rip a bomber to pieces. A single cannon shell could rip a wing off if it hit in the right place.Jugs routinely took hits from 190's and went on to finish the mission. In simulations I never warmed up to the plane; it can't turn for beans. But I was part of a massive week long argument once as to what the best plane of the war was.
    The Jug guys pretty much won the argument.
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  14. #14
    eert a ekil yzarc SpiderMike's Avatar
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    So if we are making equals of engines and our legs to the pedals...
    Then would gatorade and powerbars be Octane boost?

    And breath right strips be Cold air intakes?

    Going from platform pedals to SPD be like changing out the differential with a Ford 9"?

    A computer with cadence be like a tachometer? Too bad the cyclo computers don't com with shift lights, that would make it easier to teach someone how to shift.


    Cycling is my first love, with hot rods being second.

    Ride on.

  15. #15
    DEADBEEF khuon's Avatar
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    The P-47s actually used radial engines... not rotaries. One of the keys to the Thunderbolt's robustness was the fact that the engine was air-cooled (and huge). It could absorb hits without failure. There was no coolant system to rupture. pieces of the engine could be popping out and the thing would still run.
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  16. #16
    60mph in the 42 ring! Dave Stohler's Avatar
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    In WWII, a P47 pilot took a bunch of anti-aircraft fire and his (2100 hp rotary) engine starting sounding funny,
    Strange, since the first Wankel rotary engine wasn't built until 1957. I believe you are confusing a radial engine with a rotary.
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  17. #17
    DEADBEEF khuon's Avatar
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    Originally posted by Dave Stohler
    Strange, since the first Wankel rotary engine wasn't built until 1957. I believe you are confusing a radial engine with a rotary.
    Yes, I think that poster meant radial. A radial engine has its cylinder assembly fixed while a rotary engine has the crankshaft fixed and the cylinder assembly rotating. The advantage of course was cooling.

    The rotary aircraft engine predates the Wankel rotary. The most famous of these were the Gnome engines used during the biplane era. Ever wondered about the origins of the flying scarf? Scarves were primarily worn by early pilots to wipe off the oil (castor) from their goggles that spewing out the ends of the rotating cylinders in rotary engines. Also, it was often said that the endurance limit of an aircraft back in those days was governed by the pilot's ability to withold his/her bowel movements due to eventual ingestion of the castor oil. Hmmm... now that I mention that, I think we've found a certain commonality to biking.
    Last edited by khuon; 09-02-03 at 07:21 PM.
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  18. #18
    Senior Member djbowen1's Avatar
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    i had a 86 rx7 and a 93 rx7 tt and they were both pieces of ****, more the 86 than the other, every little thing goes wrong with those cars.

  19. #19
    The Red Lantern Rev.Chuck's Avatar
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    The rotary is a port valved motor much like a two stroke and there are issues with comprimising on effeciency and power as well as not getting optimum cylinder filling and scavenging at all rpm's. There was also the need to protect the apex seals that do not like lean running (heat) or detonation. There is also the need to inject oil into the chamber to lube the apex seals. The rich running, esp. carbed cars, combined with oil injection not always at optimum gave the cars a reputation for being smokers. As most people were used to piston motors where smoking indicates worn rings or valve guide seals, the average person figured the motors wore out easy when they were just doing what they were supposed to.
    The new motor in the RX8 uses an altered port setup, on the side of the chamber rather than in the area swept by the apex seals, to give room for a better shape (This has been a hotrod trick on the exhaust port for a long time.). The engine is also fuel injected so the precise amount of fuel is entered for that rpm.
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  20. #20
    DEADBEEF khuon's Avatar
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    BTW, in case it wasn't clear what I was trying to say earlier. The aircraft rotary engine is not the same as the Wankel rotary engine. They are based on totally different design principles.
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  21. #21
    60mph in the 42 ring! Dave Stohler's Avatar
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    Just to confuse things, I once read about a 2-stroke Wankel rotary. I guess it ran, but I can't find anything online about it.
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  22. #22
    The Red Lantern Rev.Chuck's Avatar
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    All rotarys are "two stroke" in that they fill/compress/combust/exhaust in one cycle like a two stroke. It is not actually two strokes as the motor spins rather than pumping up and down.
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  23. #23
    60mph in the 42 ring! Dave Stohler's Avatar
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    Sorry, you are wrong. All Wankel rotaries use the same common 4-stroke principal (actually a 6-part process in thermodynamics, but I don't wish to confuse the matter..) as the vast majority of piston engines. A few piston engines use the 2-stroke principal (such as certain motorcycle, outboard, chainsaw, etc. motors), incuding the formerly very popular Detroit Diesel truck motors, which used a blower to scavenge the cylinder on each power cycle.

    The motor I was referring to used sparkplugs on each side, and had port top and bottom. It relied on blower scavenging, was very small, light, powerful, and noisy. I also assume it was not economical.

    Rev chuck-you seem to know only a very little about these motors, so I'd suggest you quit while you are behind. In fact, a Wankel does require 2 revolutions of the crankshaft for each power stroke, just like a piston engine.
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  24. #24
    Traffic shark
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    Dave can you be any more of an anus in your reply?

    If you feel he's wrong.. you can say you feel he's wrong. No need to make it an attack.
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  25. #25
    Senior Member late's Avatar
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    Attack, you mean like describing someone as an unpleasant body orifice? Perhaps you should heed your own advice.
    Old Man Maine

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