Wankel engine vs Piston engine

I am taking drivers ED this summer and getting a car next year, of my choice, under $30K. I saw the Mazda RX-8 and am seriously considering it. I like its wankel, but I was wondering...

What is a better engine, a Wankel engine or a piston engine?

I don't know about engines but, I'll see your wankel engine...

And I'll raise you a bastard file and a left handed screwdriver.

...

... ... ...

what

Originally posted by ChiKeyMonKey
I don't know about engines but, I'll see your wankel engine...

, I'd never heard of it before either.

Looks pretty cool though, here's the wikipedia link:

I'm pretty sure both are considered piston engines, except that one rotates and the other reciprocates.

Bear in mind that the Wankel engine hasn't exactly taken the world by storm and even Mazda only has one car in its stable that uses one.

Here's a write up on the pros and cons:

www.sciwrite.caltech.edu...

Google Search

[edit on 2007/5/31 by GradyPhilpott]

Wankels sound odd, not like a proper engine to my ears.

350, headers, glass packs=music

I do like the elegant simplicity of a wankel though.

Thanks dj77 for that animation.

Sorry there BW23, just pulling your pistons!

Nice pic DJ77!

Something tells me I would have heard about this sooner if it really was any good! and it's been around for a long time. There must be very good reasons why other companies are not using it...

Mazda seems to have made is successful. Furthermore, its being adapted for hydrogen. Dual fuel is coming, and its simple for such a simple engine.

Umm, I dont really see any similarities between a wankel and a piston engine...one has pistons, one has rotors...

Originally posted by BlackWidow23
Umm, I dont really see any similarities between a wankel and a piston engine...one has pistons, one has rotors...

Read the accompanying material and you will find that the Wankel engine is frequently referred to as a rotary piston engine.

Merriam-Webster defines a piston as something that moves back and forth, but often dictionaries are behind the evolution of technical language.

There are two basic types of internal combustion engines - the conventional reciprocating piston engine and the rotary piston engine; the former being characterised by a connecting crank mechanism (the crankshaft) which transforms the linear motion of the piston into circular motion.
[Fig 1]

Rotary piston engines do not employ a crankshaft; the linear piston is replaced by a rotary piston coupled to a rotating shaft which performs an uniform or variable rotary movement without being affected by alternating inertial forces due to changes in piston velocity, particularly at top dead centre and bottom dead centre. Since the motion produced is rotary, it can be utilised directly without having to be transformed.
[Fig 2]

www.citroen.mb.ca...

Well the Wankel, or what a lot of people just call a rotary engine is a proven design and simple to manufacture due to the reduction of parts involved. Because it does not have any inertial forces like an internal combustion engine with pistons and a crankshaft, it can also rev higher. I saw a dragster powered by a rotary once, that was even turbocharged. It was quite a site. But, I did find a nice little clip of an RX-7 at the dragstrip:

Mazda came out with the rotary engine in about 1973 +/- 2 years, and made a big deal about it. As I recall, there were quite a few maintenance probems with the cars, but I don't know if they were inherent in rotary engines or if the Mazda design had some bugs in it. In any case, they switched to standard engines after a few years. I didn't know they still even made a rotary. I suggest you do some research on problem history before you buy the car.

Occam

Wankel engines have MASSIVE problems with apex seals.

So you go through lots of oil (and seals). Ive "heard" they've fixed a lot of that on the new rx-8 but my buddy has one and he still goes lots of oil. I cant remeber exactly, but I think he said it's normal HA

Should have bought a vette

the problem with the wankel engine is fuekl comsumption. it haa a much bigger one hence the reason it never took of.

the rotary engine is a nice advertisment, like the hemi, but not what it is cracked up to be.

straite engines give the most bang for your buck.

smooth and torquey. Skyline uses them, BMW M series uses them, Ford Falcons use them.

the RX8 is a toy and has never ever kept up to to Nissan or Toyota who would never consider a rotary for any application.

I love the RX-8. Someone mentioned fuel economy, but 26mpg sounds pretty good to me.

30k dollars I would get something better than a rx8. I've never heard of a wankel going past 100k, of course that was the earlier turboed models.

Wankle engine's used to have major problem's with the rotor seal's as stated above but in recent years these problems seem to have been overcome by mazda ( the problems effectively bancrupted NSU one of the original companies to use the engine in cars ) mazda have also achieved some success with this engine at le man's. This engine has also been used in motorcycles by DKW Suzuki and most recently by Norton. Norton won several British superbike season's with a version of their bike although iirc they were never allowed to race within the international superbike races due to a dispute over the exact size of their engine and the way that the rotor rotates as well as moves within the chamber? A rotory Norton also won a Isle Of Man TT race ridden by Steve Hislop iirc?

Just from first impressions, I would say that the wankel is a much more efficient engine than a traditional piston engine.

You could also combine two wankels and come up with a monsterous, pseudo frankenstein Le Mans style 787 engine. (just saw that in last months Sport Compact Car magazine).

Anyone crazy enough to try?


[edit on 9/12/07 by Don Wahn]

If you dont care about reliability get a Rotary engine car, they seem to consume oil badly and generate alot of heat which wears out the apex seals. If they were so awesome for everyday use people wouldnt swap them out for LS1s in RX7s. The reason being the LS1 weighs the same because of its aluminum design vs the wankel cast iron. Also more HP with the same gas mileage. Just get something simple that you can work on unless you have big bucks to fix it when it breaks. Also does it snow by you? Cause that car will be # in the snow.

reply to post by PlausibleDeniability


ok ok ... looks like I need to do damage control on rotary bashing. First, let me say, I have owned big blocks, small blocks, 4 cyl, 6 cyl ... and of course rotaries.

well, did you know, they designed a Vette one time with a rotary engine? Rotary Corvette Prototype '73 more on rotary corvette


Or ... how about the DeLorean? what the DeLorean should have had - not a flux capacitor






I understand the ignorance, and, since we are in BTS, I will let it slide.



The mention of the oil loss. Let me clear this up first. The way Mazda designed the engine is as such ... oil is INJECTED into the engine in small quantities to LUBRICATE the apex seals. Of course, in this method, it uses it up. This system is run by an air pump, the higher the revs, the more oil pumped for more lubrication. Thus, it could burn a quart over 3000 miles driven slow, or burn a quart in 500 miles if you drag race from light to light or drive at 7000 rpms (yes, some people try not to drop below 3000 rpms in daily driving).

The problem is ... if people don't follow manufacturer's maintenance ... there could be a problem ... that isn't Mazda's fault. Keep it with oil, keep the oil clean. A VERY important part is the cooling system. The engine runs hotter than a piston engine. What that image below doesn't show you is all of the cooling tubes that flow around the outside of the chamber. IF you allow your cooling system to fail, or don't keep up on maintenance (changing fluid, etc.) then, of course, it will overheat ... overheating will cause metal to change shape ... it will also cause the fuel to pre-detonate ... when the fuel explodes before it is suppose to, THIS can tear up apex seals.

Over the years, Mazda increased the apex seals width, experimented with different materials. People who heavily modify their engines have the rotors changed to accept 3 mm seals and use ceramic.

A stock rotary motor in the 2nd generation platform put out approximately 150 hp, the turbo about 185 hp ... out of a 1.3 L engine that could rev to about 8000 rpms. a in 89-91, it was increased to 200 hp for the turbo and about 165 hp for the non-turbo. In 93, the sequential twin-turbo raised it to 250 hp, but a drastic rise in available torque makes it a powerful beast on the road ... since RX-7s (and 8s) are known for their near 50/50 weight distribution and weight around 3000 lbs.

BTW, a RUNNING rotary can weigh as little as 150 lbs ... so power to weight of the engine SLAUGHTERS a LS1 engine ... so does the hp to cid. Very few people actually put V8s in the chassis, and it is highly frowned upon by most owners of the vehicle ... a major reason, it throws off the handling and balance of the car with all that extra weight.

The thing about a rotary, it has a lot of untapped power. If you put a full true dual exhaust (one pipe for each rotor from engine back at around 2-2.5" id) you will gain a large hp boost. If you want more, you will have to port the engine, since, stock ports are restrictive ... for best streetability, go for a street port ... bridge ports and j-ports are larger, but it roughens the idle, so more suitable for racing. To free up currently available horsepower, get a lighter flywheel, lighter rim and tire package ... you can even buy lighter rotors.

Since the RX-7 and RX-8 have a 50/50 weight balance, they drive fine in the snow ... they don't push/plow. With any rear drive vehicle, it depends on the control of your foot on the gas pedal. What the poster before did is try to manipulate perception. That LS1 is just as hard to drive in the rain or snow. I know, I drove a 70 Monte Carlo with a drag modded 454 in it which got about 5 mpg. All three of my rotaries got between 17-28 mpg ... depending on how I drove them. My 75 Pontiac Grand Ville convertible with a 400 got 9 mpg. My 76 nova with a 350 got between 10-15 mpg. my dads 79 El Camino with a 350 got about 8-12 mpg (gearing on that one).

I have driven many vehicles with many different engines. I have studied my own cars a lot, for I was always passionate about them. I plan on owning another Grand Ville as well as another RX-7.

I am giving you NON-BIASED info and opinions.


btw that 787B LeMans 4-rotor ... won its first year ... they banned rotaries or heavily restricted them in races since ... I thought about racing one, but there are weight and class restrictions that murder your ability to compete ... putting your 1.3L with a weight penalty against a BMW just doesn't seem fair ... rules may have changed since, but that was 5-10 years ago.

I will give you one hint, and this goes for any car. The faster you drive, the more gas you burn. The numbers advertised are highway mileage. I drive a Hybrid now, and, if I gun it from red light to red light in the city, I will get in the mid-30s in mpg. If I drive defensively and respectfully I get in the mid 40s to mid-50s in the city. If I drive like a 'grandpa' I can get over 60 mpg in the city on full tanks repeatedly. I have also gotten close to 90 mpg on the interstate going from texas to florida. It is all in foot control ... using the least amount of gas pedal to accelerate and maintain speed, maximize costing, timing red lights to conserve momentum ... that is what saves more fuel than anything. If you foot is always on the gas or brake ... you mileage suffers.

If you want any tips on driving economically or want me to hunt down my old rotary links, feel free to U2U me. I know more about those two things than I have use for.

The RX-8 is nice. I wanted to buy one and put a supercharger on it ... though the smooth revving of a naturally aspirated rotary is something else. Just don't over-rev it. The reason is, the eccentric shaft is designed for a certain load. As you increase the speed, the force of the weight of the rotors increases. It is hardened for a certain rpm range in mind. I think the RX-8 is 9 or 10k. This is the highest for a rotary production. I believe the 89-91 non-turbo was 8500 rpm.