Hercules

That in its evolution, the piston engine has had tens of THOUSANDS of engineers developing, improving, and trying to perfect its design.

The rotary in its evolution has been touched by fewer than 100 engineers. And to make the progress they have with the limited funds, engineering talent, and apparent lack of widespread acceptance (though that may change with the RX-8!), it's doing pretty damn well with a 1.3L engine making 250 Naturally Aspirated horsepower.

Imagine tens of thousands of engineers working to improve the rotary, over the span of time the piston engine has had.

Which would be the better engine?

A debate that's open ended, let's all keep it clean and contribute!

lefuton

you know, im genuinely surprised we still rely on fossil fuels running engines that turn out less than 50% efficiency. im looking forward to the day (hopefully in my lifetime) that any car with a combustion engine will be more of a collectors item as opposed to a mode of transportation.

wishful thinking perhaps, there are still segregated proms in georgia >_<

i really do like piston motors, they go from ridiculously finely tuned f1 motors to amazingly gas efficient 3 bangers to monstrous diesels. but the rotary i love most because of its finesse. one of the things about it i guess is it's much more simple than a piston motor, which, you could say, gives less room for improvement without some serious revolutionary ingenuity.

as for which engine would be better given the same amount r&d poured into them... i think it really does depend. the rotary is ingenious and very good at what it does. but with so many more parts and factors you can change, the piston motor is more versatile. variable valve timing is easier, 2 stroke is possible, you can bore and stroke piston motors easier (ie, same size block, still can use your same motor mounts).

i'd be real interested to see some massive 10L 4 rotor diesel motor... that would be...interesting so i guess the only conclusion i can think of is that the rotary would probably not have traded places with piston motors but probably would have had much more of an application niche...along the lines of (if you care to imagine) all the 2 stroke bikes/boats/snowmobiles were rotary instead and 4 stroke piston motors still had their share of applications. and now i've found myself rambling...it's late, i'll shut up now

Lensman

I thought it was an excellent reply!

Supercharger

Mazda could build a 4-rotor turbo Top Fuel Dragster and try to beat the current 1/4-mile records (4.477 ET , 332.75mph).

http://www.nhra.com

http://www.topfueltour.com/english/teknik.htm

6000 hp Supercharged V-8:

Y&Y

I'm just a newbie when it comes to the Wankel. But I was wondering was the rotory engine ever applied to motorcycles? Well cuz since the motorcycle is pretty light as it is compared to your average automobile. And the wankel isn't all that torquey. But I don't know much about motorcycles either?

Any thoughts, info, facts? Please enlighten me with all your knowlegdes.

FamilyGuy

Y&Y,

Yes, the Wankel was applied to motorcycles. I forget which models (A Google search should help) but there were quite a few.

Also, the present, naturally aspirated incarnation of the wankel has relatively little torque. On the other hand, the turbo'd 3rd generation RX-7 had the same size engine - 1.3 liters - with 217 ft*lbs of torque. That's very reasonable.

You can build very torquey Wankels - the question is, how does the mpg and pollution compare to an equivalent power piston engine (I have no idea).

DonG35Miata

Hercules, Norton, Suzuki, a few others. Check out www.monito.com for more info.

I agree with Herc as to the relative lack of rotary development and there is potential in the design. However, I think there are limits to what can be achieved with the design due to its nature. How would you improve the basic design of the wheel? You can't. Porting, intake, exhaust, and materials used are about the only areas to work on in a rotary. The basic layout of rotor and chamber is fixed.

In contrast, in a piston engine you can change valve gear, valve timing, combustion chambers, more bore/less stroke and vice versa... I could go on but there are lots of areas to tweak with potential payback, compared to the Wankel's rotor and the chamber.

I'd love to be proven wrong, but I don't think a rotary without forced induction will ever make a lot of low-end torque unless you add a lot of displacement, which will really kill fuel economy as well as adding complexity. Those spinning rotors are thirsty. You can apologize for and rationalize it all you want, but in C&D's test the RX-8 turned in lower MPG than a G35 coupe that is much heavier, yet has more horsepower and almost double the torque. That is pretty sad. Yeah, the RX-8 was driven hard, etc... well, I am sure the G35c was too! No excuses. The fuel economy is sub-par for a car of its weight and performance, ESPECIALLY the real-world 7.5 sec 5-60 street start.

I am not bashing the car since I am no longer on board; it's just how I see it.

wakeech

you're right about a few things Don, but not all of it.

it's true that you can't just change the geometry of the rotor and chamber willynilly as one could with a piston motor, but why would anyone want to?? as a performance motor, you can't get a better "bore to stroke" ratio, and it's impossible to fit more displacement in a smaller package (trust me, it is). the low mass of the moving bits in the engine and obvious mechanical simplicty really does lend itself well to high rpm operation (apparently the thermal efficiency increases with revs too)... in racing application, even the most basic steps to improve breathing (the invincible P-Port) has been relegated into submission, because it's just too unfair.

in the real world, though, it's true: the wankel is a bit too thirsty.
apperently the EPA doesn't believe Mazda's 20/30 (9.1/100km mixed, i think) claims, but until we get real-life reports from real people (HI JSG!! EASTMOONsan!!) we can't truely know... magazine tests are, well, magazine tests: i don't really believe that a few hours, or even a day or two, with a car is really enough to know it, it's basically just a first impression.
and BTW, you can still have a "real-world" 5-60mph start that's about 6 seconds: depress clutch while rolling -> rev motor to 7k -> drop clutch in first and roll the burn-out

it's true that a low displacement engine will not make much force per turn, especially one with such a short stroke, but this is univesally true for wankel and piston alike. take a look at any 2.0L motor: does it produce significantly more torque than the RENESIS?? no.
even a really really oversquare 2.6L won't make 160lb/ft if it's stroke was comparably short to the wankel's (which is impossible, since the valves wouldn't fit into the combustion chamber, even at BDC ).

but, i know that with enough development the wankel could be made better: as good as a piston motor in fuel economy?? probably not. performance?? damned straight it's better, and always will be, hands down.

...i'm willing to bet $20 CDN that if the RENESIS (or wankels in general) stay in development with Mazda (with a real budget: not fanatics doing unpaid overtime, as i would) that a wankel motor will be the first 4-stroke (Otto cycle) engine to reach 10k at redline from the factory. eat it Honda, eat it good.

wakeech

an interesting idea... i think Mazda'd be better off (obviously) trying to make a 6 rotor ahahaha...

that way, it's a "sane" 1000hp per rotor... only...

edit:
let's see... 6000hp * 5252 / 11000 rpm = 2864.7 lb/ft / 6 = 477.5 lb/ft/rotor ... CHILD'S PLAY!! ahahaha...

babylou

Ummm, there are plenty of 4 stroke motorcycles with redlines in excess of 10,000 rpm.

I will send you an e-mail as to where you can remit payment of your $20 CDN.:D

wakeech

oops!! i forgot to add the PASSENGER CAR MOTOR part to the "4 stroke" bit. :p

DonG35Miata

He got you fair and square, Wakeech... pay up!!!!! It's only $ CDN anyway- only around $13 US. Do the honorable thing and puy, just don't wager next time...

Why would one want to? Well, in piston applications an engine designed to be more of a torquer can be given a longer stroke, a high-revving HP mill, a shorter stroke. Just as I was saying, more options for the engine designers. If a Wankel with a longer stroke for more torque could be developed, it could find itself in other applications besides sports cars. And high revs are not desirable all the time. If I was getting the RX-8 I'd trade 1,000 rpm of redline for 25 more lb-ft of torque under 5,000 rpm. (BTW my Cooper S was completed Wednesday! )

Imagine: Mazda is going to go ahead and introduce an Amati line after all, starting in 2008. The flagship will be an S-Class sized sports sedan weighing 4,000 lbs with a three rotor powerplant, or 4,200 with a 5.5 liter V8. Horsepower is comparable at 330, but the V8 makes 350 lb-ft of torque@ 4,000 rpm and the 3-rotor Renesis makes 250 at 5,500. Peak HP is achieved at 5,500 RPM on the piston motor, 7750 in the 3-rotor.

Which engine has the best chance of making the car successful? Sure, all of us would take the 3-rotor with a six speed (if offered- what a car!), but the general public would want an automatic, and in that case my money would definitely be on the V8.

I am sure Mazda will surprise us with future developments, but as I said, other than intake and exhaust tuning, the Wankel is a lot like the wheel in that the basic design can't be improved upon, or developed further. It will take a real breakthrough for it to be competitive with the piston engine in automotive applications other than sports machines.

wakeech

oh no no, i'm not saying it's not a niche engine: it most certainly is, and that's why i love it so much...

yeah, i'm not some kind of anti-piston fanatic, i'm just a simple rotary lover, and i love it because it's maybe the single best architecture around for a performance motor...

btw, that 2.0L 3 rotor would have to be in a pretty sorry state of tune to make only 330hp :p

...and about the $20: i'd send it, but Lou hasn't mailed me yet like he said he would... but i really did mean passenger cars specifically, but i was snoozing, so i guess i lost. *shrug*

lefuton

why's that? 1.3L renesis makes 250, or if you wanna break it down, 125 per rotor. 330 for 3 rotors is 110 per rotor, that ain't that bad at all considering you are no longer counter rotating the rotors and it's not as well balanced as a 2 rotor.

neit_jnf

I believe there are still a few more areas that can be researched, maybe increasing compression ratio and using direct injection just to name one?

DonG35Miata

I love it too and see, I would like to see it move BEYOND the niche. Remember the NSU Ro80, the Mazda RX-3, 4, PU.... OMC rotary outboard... rotary lawnmowers... rotaries everywhere. I don't think we will get to the point of that much rotary proliferation again as many manufacturers have made their minds up against the rotary, but with a breakthrough that improved fuel economy and torque we could see more rotary applications such as a RWD Mazda sports sedan to compete with the G35/330i/IS300, aforementioned rotary luxury car, a modern-day RX-3 (someone brought this up eloquently) etc.

Good point- the kickass Mercedes Rotaries that made gobs of horsepower alll had direct fuel injection, and I think peripheral ports on intake and exhaust. Who knows what would happen if direct injection was put on the side-ported motor?

Mazda claims about the new rotary's improved efficiency are overblown. The engine is thirsty, as they have always been. In the fnal equation I think it is this thirstiness that is the Wankel's biggest drawback, followed closely by lack of low-end torque. In fact, the two are related because if the Renesis had more torque, you wouldn't have to spend so much time in the top part of the power band. Lick the fuel economy problem, and then you have it made. The engine can see more applications than it has before, and BIG rotaries to power that luxury car could be produced. Perhaps something with 3.0 l of chamber volume as opposed to 1.3 today, all out of two rotors. No torque problems now... what a beast that would be!

DonG35Miata

BTW, I of course know the RX-8 is intended to compete with these cars. What I was thinking is something a bit more conventional. A lot of buyers will not consider the RX-8 a direct competitor because of the size and layout of the car, which is more sporting than sedan.

babylou

I can't take money from a poor *** college kid. Take the $20 and add another $20, drink till the women are cute and take one home and show her your knowledge of the Wankel.

babylou

I too would love to see a larger displacement rotary even at the expense of some of the rev range. A 1598 cc rotary with the efficiencies of the Renesis could produce 260 hp @ 7,200 rpm & 200 lbs-ft torque @ 5,000 rpm. This is still a high revving engine with a redline at maybe 7,700 rpm. This engine can be made with the simpler two stage induction system of the low power Renesis. I see this as the perfect sports car engine. Smooth. Great sound. Good but not great torque. Good but not great power. Super lightweight. Decent efficiency. No cost increase over the Renesis, except for all new tooling (that is a real big except).

I think the future of the rotary is bright. Big strides in torque, power and efficiency can be made if someone can develop variable port timing and geometry. Don't laugh. It can happen. I know because I am looking at a sketch of one at the moment.

Hercules

3 rotor engines that I've seen make in the neighborhood of ~500 horsepower and still weigh less than your typical V8 engine.

Thing is though... they are thirsty bastards

wakeech

variable geometry?? heh heh heh... whose sketch?? yours??

btw: i don't need the booze to get the women i take home "look pretty" ... not to mention the summer job has made me anything but poor *** :p

...would ANYTHING that makes 500 hp not be a thristy bastard at WOT??

Smoker

Good call, lou.

Make sure you show her the E-shaft and your high RPM.

Supercharger

Group C Sportscar Comparison

_____________ 1992 Mazda MXR-01 _____ 1991 Mazda 787B

Engine _________ NA 3.5-liter V-10 _________ NA 4-rotor

Le Mans
Qualifying Time _____ 3:34.329 _____________ 3:43.503


http://wspr-racing.com/wspr/results/...emans1992.html

http://wspr-racing.com/wspr/results/...emans1991.html

Mazda shows that a piston car is faster than a rotary car.

1992 Mazda MXR-01

wakeech

ahahaha... i knew it, i KNEW you'd post something like that... ahahaa...

...i'm looking into it. omfg... ahaha... the only reason that Mazda used the piston engine there was because they had to: the year after the 787B's COMMANDING victory the wankel engine was disallowed :p

Farsyde

thats also 10 chambers vs. 4 so giving up 11 secs does suck but its not too bad.