The REAL advantage of a rotary engine.

Discussion in '1993 Mazda RX-7 JM1FD' started by budgy, Feb 10, 2003.

  1. Rotary engines are incredible, you hear a lot of people talking about how good the hp/l is. But the thing is the hp/l on most rotary engines is really not all that spectacular. Now here is why, take the high powered JDM RX7 that actually has about 280 horsepower. For a 1.3 litre engine that is 215 hp/l, on an engine that is hardly stressed. Rotary engines make this much power because they fire twice every combustion cycle, so it should be rated as a 2.6 litre engine, this makes 112.5hp/l, still a good rating, but really for an engine using forced induction this is not spectacular by any stretch of the imagination. I mean the Lancer's make 140hp/l with forced induction, and like the rotary engine is very unstressed.

    Now before you start flaming me for bashing the RX7, here is why rotary engines are great. Rotary engines have very few moving parts and are very small, 1.3 big engine, that displaces as much as 2.6, this is very good for weight. If you have ever seen the engine bay of an RX7 it is very umm empty. The engine is very small and is actually tucked behind the front axle very close to the middle of the car this technically makes the car a mid engine car. And it gives the car a great weight distribution. This is why the RX7 is such an autocross demon. And that my friends is why rotarys kick ass.
  2. Re: The REAL advantage of a rotary engine.


    thanks for informing us!!
  3. Re: The REAL advantage of a rotary engine.

    and that is also the reason that rotaries guzzle shit loads of fuel
  4. Re: The REAL advantage of a rotary engine.

    They guzzle shitloads of fuel for a "1.3" litre engine they dont guzzle it that bad compared to lots of other cars.
  5. Re: The REAL advantage of a rotary engine.

    That's true. And the reason why it may guzzle gas is the fact that is uses turbos, and turbos gives a lower gas mileage.

    That probably why Mazda is now making their Rotary cars natually aspirated, like putting the new Renesis rotor in the RX-8 and the new RX-7 project.
  6. Re: The REAL advantage of a rotary engine.

    Well it is true that turbos generally decrease gas mileage,(especially in this case) but turbo with small amounts of boost can improve gas mileage on some engines, usually a diesel, it is pretty hard to accomplish that with a gasoline engine.
  7. Re: The REAL advantage of a rotary engine.

    i know this is off the subject but i really cant stand the pic that "undefined jojo" has under his name. that guy looks like a #$%#ing ass hole. uhhh no offence i guess.
  8. Re: The REAL advantage of a rotary engine.

    fukk u ***** im not the one who doesn't know how to take care of his own car "my engine over heats" #%$got that's why you add an intercooler and an intake
  9. Re: The REAL advantage of a rotary engine.

    you are a #$%#ing moron. i posted that the engine smoked a small amount but never overheated in the least bit. that was the whole point of the post. and the car already has an upgraded intercooler. besides, the car came with a stock intercooler. so i dont think that that is the problem. when you come up with somthing better go ahead and let me know. until then, i still think that the guy in your pic looks like #$%#ing reject. besides your only all pissy because i made fun of your pic. so why do you just calm down.
  10. Re: The REAL advantage of a rotary engine.

    It's you can do it with gas - it's called the 'miller cycle'.

    Mazda used it in the 929 (IIRC) with a supercharger, but it would work with a turbo too I would think (probably better, since turbo power is 'free' power more or less). IMHO they should make all their piston engines millers (more power for less displacement and weight is what Mazda - and the rotary - are all about), but it's cheaper to just make a bigger engine (superchargers/turbos are expensive).

    Anyways, it works like this:

    1. Supercharger/turbo overcharger the piston by ~25%
    2. When the compression stroke starts the intake valve is left open for the first bit of the stroke and the overcharge is pushed back out

    Strange as it sounds, this improve effeciency by ~20% - giving you more power for less gas out of a smaller engine (the fact that smaller engines have less friction also helps).

    Why? Because the super/turbo is more effecient than the piston at low compression levels (think about it!)
  11. Re: The REAL advantage of a rotary engine.

    Actually, I looked it up and the Mazda miller (no longer in production as of this year) is ~17% more fule effecient than a n/a engine at the same power rating.

    Now 17% less fule will add up to a lot of money pretty quickly - but I guess the problem is convincing people that the higher upfront cost (of the supercharer system) will save them money in the long run (not to mention improve performance a bit via' the lower weight).
  12. Re: The REAL advantage of a rotary engine.

    So just because it gets fire twice during one cycle, it should be 2.6L? Dude, shut up. It's 1.3L for many other things.
  13. #13 ICEBLEU, May 6, 2003
    Last edited by a moderator: Apr 25, 2016
    Re: The REAL advantage of a rotary engine.

    Actually the spark plug fires 3 times per every rotor revolution, and the rotor turns the crankshaft 3 times per 1 revolution so the sparkplug fires 9 times per cranksft revolution.
    According to your theory the engine would be 11.7 liters, but your theory on motor size is wrong. The engine will always be 1.3 liters stock and thats that. If you want to stick by your theory then fine go ahead 280 hp from a 11.7 liter engine. Look at the facts, Link:
  14. Re: The REAL advantage of a rotary engine.

    It is not considered a 2.6 the 1.3 litre engine has two rotors each 650 cc each 650 x 2=1300 1.3 litre
  15. Re: The REAL advantage of a rotary engine.

    I dun see the bashing but 'my friend'. Learn what a 20b is wit a nice pettit racing intercoller. Its bulletproof power.
  16. re:

    you cant mesure roary engines in liters, so dont try, this is a good engine, we all know that, so lets leave it at that.
  17. Re: re:

    RX-7 Type R FD3S (a.k.a 3rd gen) has an engine called 13B-REW.
    The famous triple-rotor engine is from the Cosmo sedan, called 20B.
    That's because that is their size.

    654cc x 2 (1308cc) = 1.3L = 13B
    654cc x 3 (1962cc) = 2.0L = 20B

    See where the numbers are from?
  18. Re: re:

    Since someone went into the engine and positioning being a factor in the RX-7's autocrossing success, don't forget the lightweight chassis, and sleek design. :p It's gotta play a role in there somewhere, right? -.-
  19. Re: The REAL advantage of a rotary engine.

    The inefficiency is a result of several things.
    1. Rotary engines have lots of surface area. instead of being a small tube, the combustion chamber is a large, thin crescent shape, with much more surface exposed to the outside of the engine (the cooling jacket actually). This means more heat is transferred out of the engine, and energy is lost.
    2. They have lots of internal motion. Even though it says the engine redlines around 7-8000 rpm, that is the crank speed, not the engine speed. The actual rotors are actually revolving 3 times per one rotation of the crank.
    3. They have incomplete combustion, and would much of the unburnt hydrocarbons in the fuel mixture (the stuff that actually burns) would get pushed out the exhaust.
    4. They had intake/exhaust overlap. In order to get rid of as much of the actual exhaust as possible, the intake and exhaust valves would be open at the same time, resulting in the same effect as a 2-Stroke gas engine.
    5. The turbos do lower the fuel efficiency, but pale in comparison to the above.
  20. Re: The REAL advantage of a rotary engine.

    I believe that most of these problems are solved in the RENESIS. <A BORDER="0" HREF=""><IMG BORDER="0" SRC=""></A>

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