Why are Mazda persisting with the Rotary Wankel engine?

Why are Mazda persisting with the Rotary Wankel engine?

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Discussion

NLB

375 posts

208 months

Monday 18th April 2011
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otolith said:
A major part of the efficiency problem is that the combustion chamber has a much larger surface area than a piston engine - heat lost into the engine block is not being used to expand gases, drive the rotor round and power the car. Mazda have altered the geometry of their next rotary to reduce the problem, but it can't be entirely got around with current materials technology.
I once had the (slightly questionable, for various reasons) privilege of encountering, briefly, Keith Duckworth - who knew a bit about engines, I think - on an engine development project, who dismissed wankels as engines (the concept was developed as a pump, originally, I believe) because of the inherent thermodynamic inefficiencies due to this combustion chamber shape issue. Mind you, he got nowhere with the engine project (non car, non petrol) my company had retained him for, so even he had his limits. Still, sounds a logical enough argument to me.

As to Mazda, I think that the RX8 does sound to have its points, especially at the prices they've slid to, and Mazda have put a lot of time and effort into the concept, so one can see why they hang on to it - differentiates them from all the other Japanese manufacturers, apart from anything. The packaging benefits are unarguable, I think, just not worth the trade-offs, for me.

Edited for sense and spelling...


Edited by NLB on Monday 18th April 15:49

tog

4,517 posts

227 months

Monday 18th April 2011
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otolith said:
Lets you do things with the packaging that you can't do with a much bigger and heavier engine - like building a front engine rear drive car that has the entire powertrain inside the wheelbase (like a good two seat sports car) but has room for two proper rear seats.
Like Bristol has a five-litre V8 but still has the entire powertrain within the wheelbase and is a full four-seater. I accept it's a bit bigger than an RX8, but aren't there plenty of cars which manage it?

300bhp/ton

41,030 posts

189 months

Monday 18th April 2011
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otolith said:
Here's one being disassembled;



Here is a comparison of the external dimensions with a Honda S2000's F20C



Here is Mazda's take on the packaging benefits:



The main issue with the four pot is that it's a bit longer but a lot taller. A flat four would be lower, but wider - in the RX-8, the back of the engine is between your feet and the passenger's, so you would lose cabin space.
Cheers.

I picked the KV6 as it's a very compact motor and should be good for similar power. Reckon it'd still be a lot closer if you built such a car though. I do like the RX-8. But even if you had to add 2" to the wheelbase to get a V6 in and retain all else, I suspect most would be unable to tell one car was slightly bigger. But I guess we'll never know.

epom

11,400 posts

160 months

Monday 18th April 2011
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wow how long before wankelheads.com comes online ??

rhinochopig

17,932 posts

197 months

Monday 18th April 2011
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The Wookie said:
Haven't we been through this one recently?
Must have missed that thread - are you saying that's not the case?


Jayho

2,005 posts

169 months

Monday 18th April 2011
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Oi_Oi_Savaloy said:
Even if the packaging is awesome people are not going to be buying a car that does 20mpg.

but to the man in the street he's going to see pretty poor fuel economy and high tax?
There seems to be a few around these parts... :/ but maybe thats just the cheap petrol prices we experience... no, wait... :S

A car that does 20mpg yes, but unlike many other "sports" cars which are 230BHP, the RX8 does not require high octane to run efficiently... thats one of the major selling points I see with the Rotary. Although fuel efficiency just now does not seem great, you do save money on only requiring regular unleaded... wink haha.

I dont know, maybe I'm a little biased, I just love the idea of NA and high rev engines. wankle and Vtec yo! is just very appealing to me. smile

otolith

55,899 posts

203 months

Monday 18th April 2011
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Oi_Oi_Savaloy said:
I'm not having a go at Mazda for being alternative - just asking the question why persist with something that appears to be useless? Even if the packaging is awesome people are not going to be buying a car that does 20mpg.
They sold an awful lot of RX-8s - about 26,000 in the UK, I believe. Nissan sold about 7500 350Zs over the same period.

I don't know if they will be able to do that again. The next rotary, the 16X, is claimed to be more economical and to make higher torque; a 20% improvement being bandied about for both. Revised geometry and direct injection. Even so, that's going to be a high CO2 figure for an affordable car. The RX-7 was pitched against what would now be 40-50k cars. The RX-8 was pitched at 20k-30k cars. I think that the market which can afford the next rotary car's running costs without blinking won't overlap much with the market looking for a cheap sports car, and I think the EU's punitive anti-CO2 measures will make it impossible to sell a cheap high CO2 car. So I can only really see it coming here if Mazda go back upmarket with something that uses the packaging advantages to give the Cayman a kicking and price it accordingly.

glazbagun

14,259 posts

196 months

Monday 18th April 2011
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Because they have balls and aren't ready to sell their soul entirely to media manipulation experts and accountants just yet. Noone else has managed to sell such a practical-yet-good four-door sports coupe. Fuel efficiency and CO2 production are the only intrinsic "problems" with the wankel, as far as I can tell. They're hard, and increasingly more important problems to crack**, but the wankel sets Mazda apart from all other car manufacturers.

At a time when Honda, Mitsubishi, Subaru and Toyota all seem to have abandoned the enthusiast market, Mazda's pursuit of improving the Rotary gives them a visible and enduring engineering and petrolhead credibility.

  • incidentally, have Mazda ever tried a Ceramic block? I know Toyota tried and ICE block in the 80's, but I'd have thought the properties of modern ceramics and the cake-layer construction of wankels would work well together.
http://www.ceramicrotaryengines.com/


otolith said:
So I can only really see it coming here if Mazda go back upmarket with something that uses the packaging advantages to give the Cayman a kicking and price it accordingly.
I also think that the RX-8's fate at the hands of non-enthusiasts and depreciation might damage any further voyages into the mass-market.

Edited by glazbagun on Monday 18th April 16:06

J4CKO

41,287 posts

199 months

Monday 18th April 2011
quotequote all
I kind of like the fact the exist but the evidence is, on most criteria that they are a flawed idea.

Ok, I see the packaging thing, but people have managed to put a V8 in the RX8, or am I missing something here, does it bugger the handling or have 8 inches of engine sticking through the bonnet ?

If the process of acellerating and decelerating pistons is so inneficient, how come the rotary uses so much fuel in comparison to even a V8 ? there cant be many cars where whacking a Vette engine in makes it more economical biggrin

Development, come on, thirty odd years plus all the compatiable developments from the piston engined arena, they have had time to get it right and I dotn think the Rx8s engine can be as bad as internet folklore makes out but it is massively crap on fuel and the oft quoted issues cant be all made up, exagerated maybe but not total BS.

I really want the Rotary to work, but I cant see it happening.

And what happened to all those revolutionary engine designs that pop up and the dissapear on the new, is it a conspiracy or are they just not workable ?


otolith

55,899 posts

203 months

Monday 18th April 2011
quotequote all
tog said:
otolith said:
Lets you do things with the packaging that you can't do with a much bigger and heavier engine - like building a front engine rear drive car that has the entire powertrain inside the wheelbase (like a good two seat sports car) but has room for two proper rear seats.
Like Bristol has a five-litre V8 but still has the entire powertrain within the wheelbase and is a full four-seater. I accept it's a bit bigger than an RX8, but aren't there plenty of cars which manage it?
No, it's pretty unusual, especially in a relatively small and affordable car.

dvance

605 posts

167 months

Monday 18th April 2011
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Provided that thermal losses are the "bad guy" in a rotary wankel, then i would imagine that whomever comes up with a hybrid solution that captures those for use would be on to a winner. surely it should not be too difficult...

Jayho

2,005 posts

169 months

Monday 18th April 2011
quotequote all
J4CKO said:
Development, come on, thirty odd years plus all the compatiable developments from the piston engined arena, they have had time to get it right.

I really want the Rotary to work, but I cant see it happening.
True, we have had 30 odd years of "RX" cars from Mazda and they have had lots of time for developement, but you've also got to remember that Mazda have had 30 years to develope something themselves, whereas other car manufacturers have had the ability to work together for their engine designs. Joint ventures for new developement = More money being pumped into the projects and the use of each anothers expertise to develope. "synergy" 1+1=3.

At the same time you must remember Mazda have also given us a range of other cars working with pistons, so they've been, in effect, working on two completely different engine projects.

Oi_Oi_Savaloy

Original Poster:

2,313 posts

259 months

Monday 18th April 2011
quotequote all
otolith said:
They sold an awful lot of RX-8s - about 26,000 in the UK, I believe. Nissan sold about 7500 350Zs over the same period.

I don't know if they will be able to do that again. The next rotary, the 16X, is claimed to be more economical and to make higher torque; a 20% improvement being bandied about for both. Revised geometry and direct injection. Even so, that's going to be a high CO2 figure for an affordable car. The RX-7 was pitched against what would now be 40-50k cars. The RX-8 was pitched at 20k-30k cars. I think that the market which can afford the next rotary car's running costs without blinking won't overlap much with the market looking for a cheap sports car, and I think the EU's punitive anti-CO2 measures will make it impossible to sell a cheap high CO2 car. So I can only really see it coming here if Mazda go back upmarket with something that uses the packaging advantages to give the Cayman a kicking and price it accordingly.
I genuinely believe that the crap mpg wasn't well known at that point in time and word hadn't spread just how bad a) the mpg was and b) that the engines are actually terrible when it comes to reliability; witness the barrel-bottom prices for RX-8's now on the 2nd hand market and c) that they look a tad effete in my opinion.
I counter that with the fact that I really like the 'Chapman-esque' ethos (build in lightness) that the wankel engine gives and that Mazda have invested in to give a great handling car and the benefits to the interior that the small lightweight engine provides.
I still wouldn't buy one however.

Edited by Oi_Oi_Savaloy on Monday 18th April 16:12

otolith

55,899 posts

203 months

Monday 18th April 2011
quotequote all
J4CKO said:
Ok, I see the packaging thing, but people have managed to put a V8 in the RX8, or am I missing something here, does it bugger the handling or have 8 inches of engine sticking through the bonnet ?
It will raise the centre of gravity and move it forwards, but to be honest I suspect many people wouldn't notice.

You can do things aftermarket that wouldn't be acceptable in a production car in terms of pedestrian impact and crash performance, so what you can get a garage to shoehorn into a car is not always representative of what an OEM could produce.

Jayho

2,005 posts

169 months

Monday 18th April 2011
quotequote all
Oi_Oi_Savaloy said:
I genuinely believe that the crap mpg wasn't known at that point in time and word hadn't spread just how bad a) the mpg was and b) that the engines are actually terrible when it comes to reliability. Witness the barrell bottom prices for RX-8's now on the 2nd hand market and c) that they look a tad effete.
a) who buys a sports car or a sporty car looking for 40+MPG? I'm sorry but someone wanting that would be a mug.

b) Never heard of a well looked after RX8 having reliability issues, keep on top of servicing and dont move the car 2 meters then turn it off in cold, should be fine. Like any car, reliability is only as good as maintenance.

c) you're entitled to your own opinion on looks, again, if people didnt like the look of them they just wouldn't buy one.

superman84

772 posts

164 months

Monday 18th April 2011
quotequote all
Jayho said:
a) who buys a sports car or a sporty car looking for 40+MPG? I'm sorry but someone wanting that would be a mug.
I think the problem with the wankel is that, for all its benefits, sub 20mpg is really poor for "only" 230bhp.

J4CKO

41,287 posts

199 months

Monday 18th April 2011
quotequote all
otolith said:
It will raise the centre of gravity and move it forwards, but to be honest I suspect many people wouldn't notice.

You can do things aftermarket that wouldn't be acceptable in a production car in terms of pedestrian impact and crash performance, so what you can get a garage to shoehorn into a car is not always representative of what an OEM could produce.
Good point, suppose all that careful modeling done on the body structure goes out of the window when a completely different engine design, of a much bigger size is put in, plus with the economy benefit, the performance and reliability gains I expect you would drive it a lot more, so a double whammy on the safety front !

I think they either need to pull a blinder with the next generation or stop altogether, I cant imagine them selling any cars in the UK with the current Co2 tax rules if they produce cars with 300g/km, litterally handfuls of new registrations, a pity killing anything based on a fairly arbitrary figure which makes no difference buts thats the game they have to play and why the whole world is driving 2.0 tdi's (Sadly)

otolith

55,899 posts

203 months

Monday 18th April 2011
quotequote all
We've got a 350Z now, which was pretty much the piston engined competition.

It's a bit quicker than an RX-8 with both cars in the right gear and a lot quicker with both in the wrong gear.

It does slightly better mpg, but actually costs more to fuel because it must have super. Speaking of which, finding garages which have super has been more of a pain in the arse than checking the oil on the '8 ever was - until we bought a car that needs it, I never realised that some petrol stations don't bloody sell it!

It's massively less practical - down two seats and a load of luggage space.

The power delivery doesn't reward pushing it - it's nicer to drive in traffic, but the '8 was nicer to drive hard.

It doesn't ride or handle as well - it's heavy and feels it, but the suspension is much stiffer. There is nothing special at all about the '8's suspension, it just benefits from the weight distribution.

On the plus side, the 350Z's V6 should be (touch wood) bulletproof, you need an aftermarket exhaust on an RX-8 to make it sound as nice and although irrelevant here, the Z's interior is harder wearing.

I like both cars, but owning them (nearly) back to back gives an appreciation of what Mazda achieved by using the rotary. Realistically, I think it needs to be compared to six cylinder cars - one of the effects owning the RX-8 had was that I now find four cylinder engines horribly coarse. I wouldn't consider a turbo four an acceptable substitute.

I think that if Mazda had tried to make a four seat coupe with a V6, they would have effectively built a 3-series coupe rival - and the 3-series coupe is very good at being a 3-series coupe. The German car snobs would have turned their noses up at the Mazda interior and it would have ended up a forgotten curiosity like the MX-6.

Crow555

1,037 posts

193 months

Monday 18th April 2011
quotequote all
For it's power, the MPG is very low. You'd normally associate 20mpg with RS Audi's or modern American muscle. That said, the 350Z I believe is 24mpg, the Z4 Coupe 3.0 SE gets 33 and the Audi TT 3.2 is 27. It's not much but the picky buyer will look at all of these and quickly dismiss the RX-8.

A friend of mine works as a Mazda dealer and he noticed very early people trading them back in after buying them from new 6 months to a year later. He likens these people to those who buy things like Sciroccos or Audi TTs or whatever the flavour of the month is. I did like the R3 model before it was pulled from sale and would've seriously considered one had it not been for all the scare stories about them.

Put it this way. Scrappage on a MX-5 around this time last year was £3k. Scrappage on an RX-8? £6k.

Harji

2,196 posts

160 months

Monday 18th April 2011
quotequote all
Oi_Oi_Savaloy said:
I'm not having a go at Mazda for being alternative - just asking the question why persist with something that appears to be useless? Even if the packaging is awesome people are not going to be buying a car that does 20mpg.
Why on earth do you think it is useless? Ask me, I think i's wonderful, compact, rev's to 9000rpm. A rotary engine has won Le Mans 24 hour, people did buy the car. It's funny how people can drive a V8 and cope with it's thirst.

I drive an RX-8 and cope with it's thirst, is that so hard for people? As I have mentioned before, handled far better than a 335i BMW along the B-roads.