# Mazda's Rotary Engine **URL:** \ **Category:** Factual Questions\ **Created:** [June 9, 2004, 2:38pm UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448 "2004-06-09T14:38:46Z")\ **Posts on this page:** 14\ **Page:** 2
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [June 10, 2004, 5:08pm UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/21 "2004-06-10T17:08:08Z")
> [@jinty](#): > > One advantage Colophon didn’t mention (well it applies to UK only) is lower road tax - its 1300cc engine puts it in a lower road tax class than any of its competitors. This saves RX-8 owners £55 a year (hey, it’s better in your pocket than the chancellor’s, right?) > [UK Road Tax Rates](http://www.dvla.gov.uk/vehicles/taxation.htm) Sadly, that is not true any more. Notice on that link, the engine size bands only apply to vehicles registered before 1st March 2001. For newer vehicles, scroll down and you’ll see that the tax bands are based on CO[sub]2[/sub] emissions, and the RX-8 falls squarely in the top band, at a whopping 267g/km. (Hey, I’ve just planted some trees in the garden, OK…) And in any case, the DVLA (UK vehicle licensing authority) doubles the nominal engine capacity when classifying rotary engines (because each power stroke actually burns two lots of fuel, simply speaking). On my registration document it is classed as a 2600cc engine (actually 2616, I think). ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [June 10, 2004, 8:28pm UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/22 "2004-06-10T20:28:19Z")
> [@jinty](#): > > For any sports car, a unique selling point such as a rotary engine is a Good Thing. Hence the reason Mazda put it in their RX-8 rather than in their saloons/hatchbacks. > > One advantage Colophon didn’t mention (well it applies to UK only) is lower road tax - its 1300cc engine puts it in a lower road tax class than any of its competitors. This saves RX-8 owners £55 a year (hey, it’s better in your pocket than the chancellor’s, right?) > [UK Road Tax Rates](http://www.dvla.gov.uk/vehicles/taxation.htm) There is clearly no distinct advantage to a car mfgr to go out and invest in designing a rotary engine. There’s a litte thing called “return on investment”, and there’d be hardly any return on such investment. Thanks for quoting me out of context. I didn’t say the rotary had no advantages. The begging question is, again, “Why would anyone want to build a rotary engine?” …the cost, the time, the switchin gof resources. It’s moot, because only Mazda does, and it just sort of worked out that way. ---
**Author:** ![robcaro](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@robcaro](https://boards.straightdope.com/u/robcaro)\ **Post date:** [June 10, 2004, 9:01pm UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/23 "2004-06-10T21:01:27Z")
Here is a nice graphic animation of the workings of the Wankel engine. [http://www.keveney.com/Wankel.html](http://www.keveney.com/Wankel.html) ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [June 11, 2004, 2:52am UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/24 "2004-06-11T02:52:48Z")
> [@](#): > > Here is a nice graphic animation of the workings of the Wankel engine. > > [http://www.keveney.com/Wankel.html](http://www.keveney.com/Wankel.html) That site is really well done. One nitpick: He mixes up radial & rotary. A Wankel is a rotary engine. The one with pistons arranged in a circle common in early aircraft is a radial engine (the Gnome being the **really** cool one where the cylinders spin). ---
**Author:** ![mike1dog](https://avatars.discourse-cdn.com/v4/letter/m/ba9def/32.png) [@mike1dog](https://boards.straightdope.com/u/mike1dog)\ **Post date:** [June 11, 2004, 3:28am UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/25 "2004-06-11T03:28:34Z")
A few problems I’ve seen with a rotary engine. 1. If you roll the car backwards with it in gear, you will ruin the seals, which will have to be replaced. 2. On older models at least oil leaks are difficult to cure. 3. They have very little torque, which means you have to rev the shit out of them(not a problem obviously in a sports car). 4. LOUD. Rotary engined race cars are the only ones that have mufflers. I’ve seen people who put straight pipes on RX-7’s. Not for very long. Look at the muffler on a rotary engine it is much larger than on a regular engine. I actually like rotary engines, but their usefulness is limited. ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [June 25, 2004, 12:15am UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/26 "2004-06-25T00:15:22Z")
> [@Hail Ants](#): > > That site is really well done. One nitpick: He mixes up radial & rotary. A Wankel is a rotary engine. The one with pistons arranged in a circle common in early aircraft is a radial engine (the Gnome being the **really** cool one where the cylinders spin). They _spin??_ Does that affect the propellor, the cowling, or any other part of the engine or the plane (or the pilot)? I always thought it was neat how World War I combat planes were designed so the machine gun was synchronized–in order that the combat pilot would not shoot his own propellor off! :eek: ---
**Author:** ![Lagged2Death](https://avatars.discourse-cdn.com/v4/letter/l/ac8455/32.png) [@Lagged2Death](https://boards.straightdope.com/u/Lagged2Death)\ **Post date:** [June 25, 2004, 2:14am UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/27 "2004-06-25T02:14:16Z")
> [@dougie\_monty](#): > > They _spin??_ Does that affect the propellor, the cowling, or any other part of the engine or the plane (or the pilot)? > I always thought it was neat how World War I combat planes were designed so the machine gun was synchronized–in order that the combat pilot would not shoot his own propellor off! :eek: Veering way off topic here, but heck, this is interesting. Yeah, some of the [early radial engines](http://www.centennialofflight.gov/essay/Aerospace/earlyengines/Aero4.htm) spun, the Gnome among them, as Hail Ants has already pointed out. These are sometimes referred to as [“rotary”](http://www.centennialofflight.gov/essay/Dictionary/rotary_engine/DI129.htm) engines, but it’s meant in a very different sense than in the case of the Wankel, of course. Basically the engine and prop were bolted together, and the crankshaft was fixed to the plane. As far as effects on the plane and what not, there was no cowling over the engine, and supposedly the rapid rotation helped to cool the engine, even while it was idling on the ground. You can certainly imagine that it would. The gigantic [radial](http://www.centennialofflight.gov/essay/Dictionary/radial_engine/DI91.htm) engines used in large planes through WWII weren’t rotaries, though. No cite, but I remember reading that synchronizing the machine guns with the prop was actually an innovation that came along after the first aerial gun mounts. The earliest planes with guns mounted behind the prop had metal plates on the backs of the prop to deflect the occasional bullet. It sounds like a pretty reckless setup, but it apparently worked OK, although it wasn’t a very efficient use of ammo. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [June 25, 2004, 7:56am UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/28 "2004-06-25T07:56:19Z")
I once bought a Mazda with a rotary (wankel) engine. It was **a piece of junk!** And the company & it’s dealers were **terrible to deal with!** The engine (less than 8,000 miles on it) got to the point where driving home from my parents (100 miles) I had to stop at least twice to add oil. I was spending more on oil than on gasoline! And the oil running all thru the combustion chamber made it extremely hard to start during cold weather. Finally quit working altogether. Dealer kept it for over 2 months before eventually replacing the entire engine with a used one (claimed they had to wait for factory rep to see it before starting work, and the rep was so busy traveling around the country it took this long). Must have been a lot of engines being replaced to keep him that busy. And they couldn’t hire any more people? Then they tried to claim that this 2 months made it out of the warranty period! And when I went to pick up this ‘warranty repair’, they stuck me with a hefty bill for various things they claimed the warranty didn’t cover before they’d let me take the car. And I had to pay that in cash – all their repair work was cash, money order or certified check only – nothing that you could stop payment on. (That should have been a hint about the quality of their work & customer satisfaction (or lack thereof).) Apparently a lot of people had problems with their lousy rotary engine. Years later, I eventually got some money as my share of a big class action lawsuit against Mazda. But it’s been 25 years, and I would **never, ever even consider buying a Mazda car!** I get angry again just thinking about them! ---
**Author:** ![kferr](https://avatars.discourse-cdn.com/v4/letter/k/71e660/32.png) [@kferr](https://boards.straightdope.com/u/kferr)\ **Post date:** [June 25, 2004, 11:57am UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/29 "2004-06-25T11:57:42Z")
Mazda was the first Japanese, and first wankel engined car to win [the 24 Heures du Mans](http://www.monito.com/wankel/lemans.html) back in 1991. My friends who were there say the sound was fantastic. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [June 25, 2004, 1:10pm UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/30 "2004-06-25T13:10:34Z")
> [@](#): > > As far as effects on the plane and what not, there was no cowling over the engine, Sure, they had cowls. They were open at the bottom. [Here’s a Sopwith Camel](http://www.theaerodrome.com/aircraft/gbritain/sopwith_camel.html), a [Fokker DR.1](http://www.theaerodrome.com/aircraft/germany/fokker_dri.html), and a [Nieuport 17](http://www.theaerodrome.com/aircraft/france/nieuport_17.html); all of which use 9-cylinder rotary engines. There were a couple of adverse effects the rotary radial had. First, it’s a big chunk of spinning metal – a big flywheel. This resulted in a _lot_ of torque, which could snap the aircraft into a spin if the pilot weren’t careful. From [this site](http://www.laahs.com/art43.htm): > [@](#): > > Lastly, and despite being a ‘dog-fighter’, the Nieuport 21 had a powerful torque to the left. The rotating engine and the huge 103 inch propeller created a gyroscopic couple that made right turns very difficult. Another thing was their lubrication system. The castor oil lubricant would be flung back in a mist into the pilot’s face. Imagine these guys breathing in and ingesting all of this laxative! :eek: Must have made for some very uncomfortable missions. From the [same site](http://www.laahs.com/art43.htm): > [@](#): > > As a bonus, all the fluids’ movements -gas, oil and air- inside the rotative Le Rhone engine were outward. As a matter of fact, everything went outward and nothing returned. The lubricating oil was flung overboard once it had completed its trip to the exhaust valve rocker arms. The Nieuport used two gallons of Castor Oil per hour, and all of it was left behind in oil mist trails. There were times when pilots were obliged to land in order to answer the natural call brought on by prolonged immersion in the cloud of such laxative oil… Now imagine yourself wanting to poop urgently with a carpet of miles and miles of trees below you and not a single spot to land on sight. ---
**Author:** ![asterion](https://avatars.discourse-cdn.com/v4/letter/a/4da419/32.png) [@asterion](https://boards.straightdope.com/u/asterion)\ **Post date:** [June 25, 2004, 1:20pm UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/31 "2004-06-25T13:20:31Z")
I believe the Air and Space Museum has a couple of the early radial “rotary” engines on display, if you ever go to DC. I found it hard to see much of what they did since they don’t run or anything, but they still look neat. ---
**Author:** ![peritrochoid](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@peritrochoid](https://boards.straightdope.com/u/peritrochoid)\ **Post date:** [June 25, 2004, 1:50pm UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/32 "2004-06-25T13:50:38Z")
All the technical details and practicality (or lack of) have already been discussed. They’re not particularly fuel efficient, but to get an equivalent hp:displacement ratio and power output, you’d likely have an equally fuel inefficient piston engine. They are ideally suited for sports cars and aircraft because of their low weight, reliability, compactness, and smooth power delivery. Not to mention their high-revving nature. The RX-8 and RX-7s have a nearly 50/50 weight distribution, a difficult thing for a front-engine, rear-drive vehicle. As for the history, rotary engines have been put in a few other production vehicles, as many major manufacturers held licenses to produce them, including GM and Mercedes. Only Mazda had the determination and financial commitment to make it work. NSU produced a single-rotor convertible based on the Prinz in the '60s, and you can still find an example or two floating around collector car classifieds and in museums. Mercedes did produce some prototype 3 and 4 rotor sports cars (the C-111) in the late '60s and early '70s, but dropped the plan. I don’t know of any of those on the market. And for anyone interested in hearing a full-race prepared, peripheral ported rotary engine, do a search for sound clips of the 787B, the 1991 LeMans winner mentioned in a post or two previous. It had to be quite an experience to hear that in person. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [June 25, 2004, 6:12pm UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/33 "2004-06-25T18:12:56Z")
> [@](#): > > They are ideally suited for sports cars and aircraft because of their low weight, reliability, compactness, and smooth power delivery. Not to mention their high-revving nature. Hi revs are a bit of a disadvantage in an aircraft. 1930s-tech Lycomings and Continentals turn about 2,400 rpm and the props are bolted directly to the crankshaft. A Wankel engine, say from a donor Mazda, revs too high and will require a heavy gear-reduction unit so that the prop stays down around 2,300-2,500 rpm. ---
**Author:** ![peritrochoid](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@peritrochoid](https://boards.straightdope.com/u/peritrochoid)\ **Post date:** [June 25, 2004, 6:52pm UTC](https://boards.straightdope.com/t/mazdas-rotary-engine/249448/34 "2004-06-25T18:52:18Z")
> [@Johnny L.A.](#): > > Hi revs are a bit of a disadvantage in an aircraft. 1930s-tech Lycomings and Continentals turn about 2,400 rpm and the props are bolted directly to the crankshaft. A Wankel engine, say from a donor Mazda, revs too high and will require a heavy gear-reduction unit so that the prop stays down around 2,300-2,500 rpm. Right. I was unintentionally misleading in that. I meant that the revs are suited well to sports cars, then I added aircraft just before I posted. Ended up a bit out of context. There actually is a pretty strong following for putting them in aircraft though ([Rotary Aviation](http://www.rotaryaviation.com/) comes to mind), and IIRC, they do use a purpose-built gear reduction assembly. [Previous page](https://boards.straightdope.com/t/mazdas-rotary-engine/249448.md?page=1)