Advantages of a Rotary Engine
 

My friend asked me an interesting question the other day as we are talking about cars and he asked me this:

what's so good about a rotary engine anyway?
if rotary engines are so good, then why don't all cars have it?


and i said that it has smooth, high-revving characteristics, has a very high power to weight and a power to displacement ratio and less moving parts...

then i said that it was because of fuel efficiency and some stuff about the rights that only mazda had to build the rotary engine or something like that im not quite sure...



but after that i thought about it, and i was thinking why is the car still almost 3000 lbs if the rotary engine is supposed to save weight? i would have expected the car to between the 2600 and the 2900 lbs range.

can your typical 4banger make women's panties wet?

um...

"a typical car has 3 seats in the back without the thing in the middle so stuff can happen there"


my friend's words, not mine

The weight is due to the size. Mazda made it a GT car rather than a more "purist" car.

The advantage of size of the engine is so that it can be placed so close to the ground and so far back in the chassis that they can relatively easily get world class handling with a modern suspension.

Beyond that, there is no tangible "advantage" to the rotary that you can put on paper or get someone else to believe just by talking at them.

The people that love the rotary engine love it, drawbacks and all. Only the blind rotorheads think that it is a "superior" engine in the perspective of "what every car should have". No, it has it's place, and it's place isn't a very big one. Many other engine types out there are better in many other ways, each to their own goal, and you wouldn't try to put a steam engine on a jet plane. Each to their own purpose.

Most engines are designed to move something. Move it efficiently, move it fast, move it hard, move it long distances, move lots all at the same time, etc...

The rotary is just here to move hearts.

If your friend doesn't have one, pity him. You won't get someone to understand that doesn't understand through a simple test drive. Don't fight a holy war, don't bother trying to convert the unbelievers :)

The Rx-7 was around 2800lbs. Don't forget the Rx-8 is still technically a 4door coupe with 2 backseats that can actually fit human sized people.

Mazda did keep the weight low for Grand Touring & Models, around 3000lbs but the sport is even less, around 2800lbs... Luxuries take up weight.

The weight difference in the engine alone compared to a similar hp output engine is only maybe 100-200 lbs.

Weight reduction comes mainly from the frame materials and size. Its a balance between 5 star crash ratings and light weight metals. This car was designed in late 90's.

Design it over with today's technologies and it would probably be 300-400 lbs lighter for the same car.

The advantage...theoretically is reliability due to fewer moving parts. From a physics standpoint it should be more efficient with a continuous eccentric circular motion vs. up and down of pistons.

Bottom line. Piston engine has been refined by millions of researchers over hundreds of years where as the rotary has been researched by a few hundred over 40 years.

Your friend has the right idea !

Seriously though :

1/very high power output in relation to size/shape allowing ideal placement for c of g and weight distribution. This is the single biggest advantage.
2/Good power output in relation to weight .Has potential to be great in this regard but needs a lot more development yet.
3/Low vibration
4/Free revving - great for extended use at high rpm.

/\
This.

Also, the best way to convert anybody to the rotary is through a test drive. But I don't let anybody drive my car, so I have no converts yet:lol2:

Im a blind rotorhead.

My first RX7 (S2) weighed about 2350 and the second (S3) weighted about 2500 lbs.
The RX8 is larger and has more safety features than these cars from 30 yrs ago did.

the fd had a backseat and only weighed like 40lbs if we want to be technical :p

+1

But I do have a soft spot for Ls7's, Ferrari & Lamborghini's V12's and 2JZ's. :cool:

That's a front engine rear wheel drive issue, not a rotary issue.

Does your friend have a copy of the issue of Consumer Reports from the first time they tested a Porsche? They did not understand why anyone would want one of those when you could buy a Dodge Dart, which carried more people and bags of groceries, for way less money.

Ken

Go test drive BMW's new 4 banger. Made me wet.

This. The small size of the engine allows it to be placed behind the front axle and almost on the ground. This is the real secret of the 8's amazing handling in its price class. You don't get Porsche power, but you get Porsche handling, at half the price. It's not just the weight of the engine, but where it can be placed for balance.

As for why rotaries aren't used in other cars, it's mainly due to the fuel economy. This has been a problem with rotaries since the '70s, they just can't be as efficient as piston engines due to the design characteristics of the Wankel, and the more expensive gas gets the worse this problem is. Also, it's harder to meet modern emissions requirements with a rotary, making it hard to bring them to the US market without sacrificing a good bit of performance (or reliability, as in carbon-lock). The 16x promises to be a big improvement in these areas; if it ever makes it into production we'll see.

In any case, I'm enjoying the hell out of my 8 and I plan to keep it as long as I can, because I'm afraid we'll all soon be driving electric clown cars with electronic nannies, 20 air bags, and 500 lbs of batteries.

You can't explain it in numbers. It's like comparing scotch, you can't just look at the year and be like 'clearly this is better'. You have to taste it and find it's your thing.

Human's nature is, when they dont know something, most of the time they start talking shit about it as much as they can. That explains why rotary engine is getting all the hate that it does not deserve

I believe that rotary engine can match even surpass the power abd mpg than pistons. Dont forget the 13B-MSP is still based on a freaking old 13B design. So if 16x is really as good as they claim ot to be, rotary engine revolution might start.again

The biggest problem with rotary efficiency isn't development (though that's a factor), it's inherent in the Wankel design. I doubt that rotaries will ever be as efficient as a piston engine of the same power, although the 16x may narrow the gap a good bit if it ever goes into production.

you failed the ghey test.

O'rly Mr. Jedi?

20 years ago, cell phone looks like a brick, well, its so big.that u can actually use it like a weapon on someone's head.

now, phones are actually small and be able to outperform some super.computers from about 10 years

things change overtime u never know what will happen. there were many faults inherent in piston designs too, but after 100 something years and millions of engineers blood and.sweat...

When people ask me this question i give them one simple answer "zoom zoom"

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did u piss yourself, or just explosive diarrhea?

either one, women don't find that attractive

I tend to agree. I know all about the inherent inefficiencies of the Wankel design. That said, it's hard to look at the up-stop-down-stop-up movement of pistons and not find, conceptually at least, the rotary engine to be a more elegant, sensible design. I mean, why use hundreds of parts to do what can be done with just three? But then, I'm not an engineer, so I'm out of my league here.

Those hundreds of parts give you more parameters to develop.

Intake and exhaust timing, in particular. The Wankel gets its charge in and out via ports. No changing the timing or area profiles. The Renesis does a bit of adjustment by having three sets of ports with three induction paths, so there's some tuning available. But it's not like a piston engine where cam profiles, valve lift, positioning of the valves in the head, etc. are possible. Nor can the combustion chamber be reshaped. No Hemi Wankels. That we need two plugs per chamber says something about the less than optimal efficiency of the epitrochoid.

But none of that comes close to taking away the joy of sneering at a friend's Corvette and saying "Eeew...that has pistons!"

Ken