Rotary Engine Rx-8?

Dear All,
What do you guys know about the rotary engines like the one used in the new RX-8? Are they more reliable than the conventional engines? Have you all driven it? What do you guys think about it? Would you own it? Are they more difficult to maintain? I have also heard that they last longer than conventional engines.
The reason I am posting this in diesel discussion is because my diesel bros know EVERYTHING

[Matt L]

They have different problems than piston engines. One thing to be aware of is that they all use oil, just a bit, by design.

When the rings wear on a piston engine, you lose compression, and the engine slowly deteriorates to the point where you know a rebuild is necessary. The Wankel engine wears its rotor seals, but this does not generally cause a loss of compression. Rather, when the seal gets thin enough, it can suddenly snag on a port with absolutely no warning.

I wouldn't say that they last longer, but I would say that until a rebuild is mandated, the engine's power won't diminish.

I'd be most afraid of what was necessary to get these modern Wankels to pass the EPA's scrutiny. Perhaps they're just cleaner than the old models.

[vwbuge]

I would agree with MattL. They do not necessarily last longer than a conventional gas enginge. They DO make much more power vs. a comparable sized piston engine. Although it is hard to compare them size wise.

If you think it is hard to find a mechanic that knows a diesel engine, try finding one that will build your Wankel.

[jcyuhn]

As of 15 years ago rotary's were a lot less durable than piston engines. About 100K miles was the most that could be expected before a rebuild. Not sure where the current state of the art lies, but I would be surprised if they have caught up to piston engines.

A wankel has a higher ratio of surface area in the combustion chamber relative to displacement, as compared to a piston engine. Hence there is greater heat loss than in a piston engine. This translates into lower efficiency. As a result, a rotary engine delivers lower fuel mileage than a piston engine of equal power. A quick comparison: the 2006 Corvette has 400HP and delivers MPG of 18/28. The smaller, lighter RX-8 with only 238HP delivers 18/24. Guess which ones larger, faster, and gets better fuel economy?

In my opinion the real attraction of the Wankel was to the designers and stylists. It is a short, compact engine that opens up new opportunities in the packaging, styling, and design of a vehicle.

Lastly, wankel's are wankers. They don't make much torque, so you end up with a car that will accelerate hard flat out, but is a gutless wonder at middle RPM. The current RX-8 makes 158ft-lbs of peak torque. For reference that's less than the current crop of 4-cylinder Accords, Camrys, and Altimas - not exactly paragons of power. Floorboard the throttle at 3K RPM, and essentially nothing will happen. The 158ft-lbs comes at 5500RPM, just above the point at which 1ft-lb equals 1HP (5252RPM). So at 5500RPM, the RX-8 is making perhaps 165HP. From there the power curve presumably climgs steeply to the power peak at 8500RPM. Basically what 'ya got is a car that's dead below 6000RPM.

Basically, the Wankel is the opposite of a diesel. The former has little power throughout the RPM range with a strong burst at the top end. A modern diesel has a flat torque curve with strong power anywhere throughout its more limited RPM range. Really, the diesel is a better engine for street driving - it's more efficient and it delivers instant, flexible thrust at any RPM.

Geez, that got long,

- JimY

[pawoSD]

They put millions and millions into developing a new high tech rotary engine at mazda for their miata sports car. The result was an extremely durable, extremely clean running engine. It produces a LOT of power appearantly. Its a "three cylinder" version. Also, with the stick shift model it has a redline of 12,000 RPM. and the automatic has a 9,500 rpm redline to protect the torque converter. Yikes. I read a review on one around a year ago, and the guy said it absolutely rocked and highly recommended the manual model, nothing like shifting at 11,000 rpm! The engines also deliver almost a steady torque output across much of the rpm range, its awesome.


However, I'll stick with my 617.

[Matt L]

You call these "three rotor" engines.

Also note that the RPM of the wankel is the rotation speed of the eccentric shaft. This turns at three times the speed of the rotors.

[TheDon]

mercedes had a wankel engine at one time for an experimental/concept car.. they only made 12

[1983/300CD]

I haven't been Mr. Muscle car, but the 1985 RX-7 I had was the fastest car I have ever owned. It was very light, but it layed rubber. It had power. Fuel economy was not BAD. And it idled and picked up speed smoooooothly. I think they boast about the consistent power curve. It really was nice.

[Brian Carlton]

Originally Posted by jcyuhn

A wankel has a higher ratio of surface area in the combustion chamber relative to displacement, as compared to a piston engine. Hence there is greater heat loss than in a piston engine. This translates into lower efficiency. As a result, a rotary engine delivers lower fuel mileage than a piston engine of equal power. A quick comparison: the 2006 Corvette has 400HP and delivers MPG of 18/28. The smaller, lighter RX-8 with only 238HP delivers 18/24. Guess which ones larger, faster, and gets better fuel economy?

Lastly, wankel's are wankers. They don't make much torque, so you end up with a car that will accelerate hard flat out, but is a gutless wonder at middle RPM. The current RX-8 makes 158ft-lbs of peak torque. For reference that's less than the current crop of 4-cylinder Accords, Camrys, and Altimas - not exactly paragons of power. Floorboard the throttle at 3K RPM, and essentially nothing will happen. The 158ft-lbs comes at 5500RPM, just above the point at which 1ft-lb equals 1HP (5252RPM). So at 5500RPM, the RX-8 is making perhaps 165HP. From there the power curve presumably climgs steeply to the power peak at 8500RPM. Basically what 'ya got is a car that's dead below 6000RPM.

Very informative, Jim. Appreciate the post.

[jaoneill]

I know virtually nothing about the Wankel, other than the theory, but my daughter bought one (RX8) abt 18 months ago and loves it. She is in Chicago and doesn't put on a lot of miles she but has had no problems with it to date.

Jim

[thorsen]

15 years ago when I started college, my friend had an Rx-7 with a rotary. I was left with two distinct impressions:

1. Those engines love to rev.
2. An un-muffled rotary engine is one of the loudest vehicles you will ever hear.

[SD Blue]

Originally Posted by vwbuge

If you think it is hard to find a mechanic that knows a diesel engine, try finding one that will build your Wankel.

You have to wonder about this fact a little. I personally think the diesel engine is a little easier. Clean fuel and air, and don't mix the two until the combustion chamber.

I personally have never owned a vehicle with a rotary engine. A friend of mine, an aircraft mechanic, went through a mazda rotary and he said it was the simplest rebuild he had ever done. Split the case and everything is right there. Also, you are only doing one large "cylinder". Maybe it's being different, and simpler, just like a diesel, intimidates some "mechanics". Sometimes, maybe, they lean a little too heavy on the "can't teach an old dog new tricks" and don't want to dig into something new.

His comments were similar to those already mentioned. Keep an eye on the oil, no more than once a fill-up, and don't be afraid to rev it as that is where the power kicks in. Most of all, smo-o-oth.

[Hatterasguy]

I see old RX7's running in the import race's and they do quite well. How do you increase power on one of these? Like a regular gas engine? ECU, exhuast, injectors, turbo, exhuast??

They are an interesting engine though.

Mazda's 13B engine they used in the RX-7 was a good speorts car, that's about all it's good far. Like said, fuel usage was very high. Even the current generation RX-8 usually gets fuel milage complaints by reviewers.

They changed quite a bit over the years. Early ones were carburated. These were really quite bad because they were known for their 100K mile durability. Later ones were FI with quite a few being a Single or even sequential TwinTurbo's.

If you REALLY want power, a Cosmo from Japan has *3* rotors insted of Mazda's 2.

...and if you REALLY want to know *everything* about the wankel engines goto Answers.com

Note one of the main reasons for so much HP per Cubic inch: 3 power "strokes" per rotation of the rotor and one power pulse per shaft rotation, like a two-stroke engine. Also one of the key reasons for bad fuel economy.


http://en.wikipedia.org/wiki/Wankel_rotary

[TheDon]

ive seen kits online that can turn the early engines into a tri rotor set up ... i like the rx-7's nice cars granted you get them in good condition.. great for drift racing i know a guy that lives down the street from me.. he has two rx-7's.