ml2316

i see a lot of rotary fans talk about one of the pros of the rx-8 being its rotary engine, but i've never actually seen anybody elaborate on how or why it's better than a piston engine of similar power output. my understanding is that it has been demonstrated in many mags that the gas mileage of the renesis has turned out not to be anything special (not bad, not great) for a 250hp engine. so what's the big advantage, other than novelty?

Puppy1

Weight (lack there of) over the front wheels.

3Rotor

Power to weight
Size
Fewer moving parts (2 rotors in a housing, eccentric shaft)
higher reving
Fascinating!

tribal azn2

1. lighter

2. smaller

3. revs much higher

4. 3 moving parts

5. more realiable

6. no other cars have it

need any more?

ml2316

thanks. i guess weight is a big one and pretty obvious now that i think about it.

gord boyd

The longish Press Kit stated that RENESIS finally got weight down
to equivalent to 4 cyl. engine (eg: s2000 engine), so location
of engine and size more important.

neit_jnf

Beautiful mechanical engineering at work!!!!

An amazing piece of mechanical art!

ACRX8

Hummmmmmmmmmmmmmmmmmmmmmmmmm!:D

lbrintle

I'm one of those facinated with the rotary, but some of the above points don't seem to make sense. The engine is about the same size/weight as a high-revving 4. But the rotary doesn't actually rev high at all: 9,000 RPM is actually the engine turning at 3,000 RPM, since there is a 3-to-1 pseudo-gearing. Which also explains its lower vibrations...

I thought that pre-RENESIS rotaries were not real reliable, and it's not like we know how reliable the RENESIS will be.

Personally, I just like the amazing beauty of how it works, and how many times I had to step through the animation at howstuffworks.com before I could understand the motion of the rotor (in particular, how the output shaft rotates three times per rotor rotation). I do wonder how many of the rotary's negatives (high fuel consumption, disappointing torque at low RPMs, challenges with emissions) would have been solved if a fraction of the effort put into the piston engine had been put into the rotary. Look at what Mazda did with a relatively small engineering staff.

Hercules

Pre-RENESIS engines were not unreliable, they overheated due to inefficient cooling from the turbos on the RX-7.

Take away the turbos, they would have been bulletproof as all other rotaries in the past have shown to be.

If you take a gander around... there are cars out there with 200k+ miles on them, so it's a pretty reasonable mark of quality.

RobDickinson

Thats true, but the rotors are ballanced with each other onthat central shaft, thats why there isnt any vibration, no unbalanced movements.

Pre Renesis engines were very reliable, just not the turbo versions. With only 3 moving parts there are very few things to go wrong. One is the seals, other is rotor tips (?) Rotaries cope well with revvs, doesnt fase them, but are hurt by eccesive heat or oil problems.

The 3rd gen turbo added way to much heat , and that killed the engines. Also poor servicing re: oil causes problems too.

Rich

Pre-RENESIS rotaries have been extremely reliable. In fact, that's one of the main reasons they had such success in racing. If you read interviews with some of the guys who raced RX-7s and other rotary cars, you'll find that most of them picked their car because they didn't have the time/money/ability to work on their engine all of the time. It's not unusual for a piston engine to just last a single race while a rotary could last half a season. Properly maintained non-turbo rotaries are exceptionally reliable.

It's only the 3rd generation 13Bs that were unreliable, and some of the 2nd generation turbo IIs that were heavily modified. They were turbocharged to within an inch of their life. Properly maintained, even they were reliable, but too many people just upped the boost and blew the apex seals. Or they didn't change the oil often enough (big mistake in a rotary).


I agree with all the positives about the rotary, but to me the two characteristics I like are the way the engine contributes to the overall handling of the car and the smoothness of the engine. Because it's small and light, it can be placed far back and low, reducing the polar moment of inertia, which translates to better handling. Even without that benefit, it's amazing to come from a piston engine to a rotary because of how smooth everything is. It's not a big deal to just cruise for miles at 6k - try that with an I4! mmm... I wish I could get one. Maybe in a few years.

rotarynews.com

Not true at all!!!! The non-turbo RX-7's from the 80's go into the 300,000 mile range and up (Although I haven't heard anyone claim their engine is in the 400,000 mile range)

The 3rd gen RX-7 was the worst thing that could have happened for the perception of reliability in the Rotary. Inadiquate cooling, complex turbo system, inadiquate fuel management caused the 132B-REW's engines to fail prematurely in the early (1993-1994) models. Of course Mazda pulled the RX-7 from the market just when they were fixing many of the issues, and with the 1999 RX-7 in Japan, the turboed rotary was a reliable high-horse power machine.

With all that said, I love the rotary because:
It is a blast to drive.

The torque curve (how it pulls and pulls and pulls)

Power ++

Ease to work on (Not much can go wrong, a checklist of maybe 20 items can diagnose nearly any problem)

Engineering simplicity and genious

and RELIABILITY

RobDickinson

oh , something else that hasnt realy been mentioned.


That super flat torque curve (or line).

Ok so torque isnt that high, but its very flat, givving excelent progressive acceleration. Not a kick in the pants of the turbo, but that only makes a car harder to drive, slower to respond.

Joshua-1

In a word - Unique

No matter what else, a rotary engine is a unique piece of engineering. Uniqe enough that most people, even some who think they know cars, simply don't believe me when I tell them there are no pistons in an RX-8.

The rest of this is gonna sound like I don't like rotary engines, which is not true, but I would like to air this out somewhere and only here am I gonna get any real feedback.

Personally, although I am a big fan of rotary power, I don't think it has currently shows any real-world advantage over it's piston-pushing competitors. For example, the G35 gets slightly better mileage despite being much heavier and developing 40 more HP (and 110 more lb-ft of torque!). In a standing start, the G35 beats the hell out of an RX-8 on anything but a tire-frying redline launch (which the RX wins by a nose). Sure, Rotary power is MUCH lighter, but that lightness isn't currently translated into cars that drasticly outperform equivelant cars.

Take that same engine and drop it into a platform made to maximize it's potential and you would have a different story. I wish I could see a renesis in a 3rd gen RX-7, or some other platform designed to be as light as possible (miata?)

The reduction in moving parts is a great feature, but only if that translates into increased reliability over piston engines. I have run 2 toyota, a jeep and a honda engine over 200,000 miles each and the worst thing that ever happened to any of them was a broken timing belt. Neeless to say, I find this kind of reliability impressive. I haven't found any rotary powered vehicles with 200,000 miles on the original engine for sale in my area, but to be fair if you did have 200,000 miles on a car you were selling, would you advertize it? It doesn't mean rotary power is any less reliable, I just don't have any experience on it.

Put another way, I was once involved in the marketing of a paintball gun whose big advantage was "only 2 moving parts". Fact was, those 2 parts were broken 50% of the time. It was frustrating, but an important lesson. Moving parts do tend to break more, but reducing moving parts will not always mean better reliability. Also claiming so few moving parts is also misleading, since there are LOTS of moving parts outside of the engine block that, if they break, will still result in an engine that doesn't run.

Another great strength of the rotary is it's nearly unlimited revs, but again this is an advantage that doesn't translate well into a car that goes to work and back 99% of it's life. If you hit 9000rpm in traffic, you probably have issues that need to be delt with elsewhere.

Lest you think I am some naysayer or troll, I am ANXOUSLY awaiting the RX-8 and it will be the first car I have ever bought new (I already have a $10,000 down payment set aside). I would not have chosen the RX-8 if not for the renesis. If the RX had a banger engine I would have gone with the G35. So I am a big fan, I just have concerns

Sputnik

Personally, it is the unique feel, response, and sound that no piston engine has. Some people might try to explain it with technical stats like size and weight, and while those things have something to do with getting it right, the real reason is the way it responds and feels when driven. The only way to completely understand is to drive one yourself.

People who don't drive sports cars and/or have never driven a Miata will ask things like "what makes it so special, it doesn't have any power". They actually believe commercials that call a car "sporty" simply because it has a big engine, but they are "limited". Some people might try to explain it with stats like weight, wishbone design, etc. And while those things have something to do with getting the car right, the Miata is a fun car because of the way it feels and responds to the driver. And the only way to understand is to drive one yourself.

---jps

Joshua-1

Now there is an argument I can get behind. My 93 Probe GT felt faster and was definetly more fun than my 97 Taurus SHO- even tho it had just over 1/2 the power. Theres a lot more than numbers, and even track performance. What truly matters is the smile factor, which I expect my 8 will deliver on in spades.

ZoomZoom

Well said!!!

jtimbck2

For me, it's the smoothness and lack of vibration, especially at high revs. Nothing beats that rotary hum!

vipeRX7

something else ...
The rotary racing record!
Mazda is the first and only Japanese automaker to win Le Mans, and the only automaker ever to win without using a reciprocating. Now, considering that Mazda is not a particularly large or powerful company, and given that a lot of other large and powerful companies were racing against them, I find this very impressive.
Oh yeah, by 1992, Mazda had won 106 IMSA titles. Runner up for this record, the porsche 911, had less than 65.
And also--you know a car is successful when organizations regulate it out of racing!

RacerX7FB

Above all engines...Rotaries are simply COOL

Joshua-1

I think the rotary may have been regulated out of racing not because it was too good, but because it was too exclusive.

That is to say, because Mazda is the only manufacturer with the capacity to produce Rotary powerplants, if their engines are superior the winner will always be Mazda.

Unless I'm mistaken I believe Mazda has exclusive worldwide patent rights for automotive application of Wankel engines. So assuming that the rotarty is a fundamentally superior design, there would be no point in racing piston engines against it, and noone else could develop a better rotary either.

The obvious solution is to either adjust the rules in very complicated ways (how DO you compare a piston engine to a rotary?) or disallow the rotary entirely, at least untill you can figure those rules out.

Rotary engines are not even CLOSE to the first technology disallowed by a sanctioning body. Nearly all of these technologies had one thing in common: The competition had no access to the technology due to patent rights.

So while I think banning rotary engines is the wrong decision, I can understand why the decision was made. Imagine if Ford had exclusive rights to Reciprocating combustion engines and everyone else had to use steam or something.

Puppy1

I think you are mistaken. Mazda used to have to pay royalties to NSU until the late 70's. The wankle engine concept is now in the public domain.

RobDickinson

But Mazda have tons of patents on Rotary improvements which make it hard for anyone starting from scratch to catch up.

As for competitive racing I dont see why they cant impose restrictions/wqeight penalties to rotaries to even the feald as they done in the British touring cars for audi 4wd's.

Sputnik

I think it's more of a matter of sanctioning bodies needing to keep everything on an even playing field, than patent rights or anything. You had it right the first time when you were talking about trying to figure out how to level out a piston engine with a rotary, or a turbine engine for that matter.

---jps