Autoblog

Would love to see Mazda do a ultra-light-weight mid-engined rotary sports car.

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right, because you are some engineering god who designed the laws of physics and knows exactly how far the rotary can go. And hell, if the ceiling of the rotary is winning Le Mans, there's no problem with that.

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You're a freaking genius. You should put in an application to Mazda's R&D department and show them a thing or two.

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Right, because using an engine that is simpler to work on because it has considerably fewer moving parts and has just as much horsepower for an engine twice it's size is a bad thing. Give me a break.

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@seoultrain
@RCChris
@3seriesisking

You guys should inform yourselves before you post.

GM, Mercedes, Ford, Toyota, Chrysler and I’m sure a few other manufactures I’ve forgot to mention, all poured millions of dollars into rotary engine development and all came to the same conclusion:

The rotary engine is vastly inferior to the piston engine in several key aspects all inherent to its design.

The long irregularly shaped combustion chamber results in extremely poor burn of the air fuel mixture; this results in poor fuel economy and high emissions. Just take and look at the size of the catalytic convertor on an RX7.

The combustion chamber has a very high surface area to volume ratio compared to a piston engine. Several times that of a piston engine in fact; at least 5 times if I remember correctly. This results in excessive heat losses on the power cycle; meaning much more energy is lost to the cooling system rather than being converted into mechanical energy compared to a piston engine. Again this means much poorer fuel economy.

The rotary engine has sealing issues and simply cannot operate at high cylinder pressures like a piston engine. This means lower efficiency and worse fuel economy.


Those are just a few key points why it is vastly inferior to the piston engine. If you would like to learn more you can pick up the latest edition of the SAE Mechanical Engineering Internal Combustion Engine text where it goes more into depth about it.

This engine is simply a dead end as you will read for yourselves.

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Agree with the above poster. All the rotary engine fans out there love to talk about the amount of horsepower per liter of displacement. In terms of fuel consumption it barely gets the same amount of power as a plain old piston engine from a given amount of fuel, and thats with a lot of gimmickry. Basically its just not as efficient as a piston engine.

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Yes, a bunch of other companies tried the rotary and dropped out because they didn't deem it a worthy investment. All that means is that they ran out of money. It's pretty much a given that companies would be wary about spending money on unproven technology, which is exactly what rotaries were until fairly recently.

The rotary has its disadvantages, which you do a good job of pointing out, but it's not without its advantages. You cannot ignore the packaging of the engine, which enables it to be mounted lower and closer to the center of the car, which gives it a lower COG and Center of Inertia. It also has less parts, smoother operation, and higher redline. Hell, the engine even gets stronger as time goes on.

As for the efficiency/power issue, 19 mpg for 230 hp in a 2900lb car is not good, but it's not horrendous. The upside is that methods for improvement are pretty apparent. Such improvement can come from reshaped combustion chambers (to improve that surface area issue you brought up), direct injection, and forced induction. All these changes have been rumored for mazda's next rotary, so before you just assume the rotary is dead, at least be open to the idea that the 16X may solve many of the previous rotaries' problems. As a gearhead, surely at least a part of you is rooting for the success of a completely different form of engine.

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What you said is simply completely false and well as stating a logical fallacy; you said that companies are weary of researching an unproven technology. Well the whole purpose of R&D is to learn if something will work or not.

The rotary engine was not abandoned because these companies ran out of money. Realize that during the early 1970’s, GM for example controlled 50% of the North American car market, the largest and most profitable car market in the world. This was a company with essentially limitless resources at the time. During this time the industry believed that the rotary engine was the engine of the future that would make the piston engine obsolete. Every major manufacturer had a rotary engine program which was perused aggressively. It is absurd to say that all of these companies ran out of money, yet Mazda, which by comparison was merely a tiny cottage operation at the time, was somehow successful. Keep in mind that in 1973, $1 is nearly $5 in 2006 ( http://www.westegg.com/inflation/infl.cgi ).

So now you probably get the idea of how seriously rotary development was taken and GM’s program was well into the hundreds of millions in today’s dollars.

When I said that they all realized that it was an engineering dead end, this is not my personal opinion, but simply a historical fact.

“The rotary has its disadvantages, which you do a good job of pointing out, but it's not without its advantages. You cannot ignore the packaging of the engine, which enables it to be mounted lower and closer to the center of the car, which gives it a lower COG and Center of Inertia. It also has less parts, smoother operation, and higher redline.”

This is all very true but also made completely irrelevant when one considers its poor emissions, fuel economy and reliability.

“As for the efficiency/power issue, 19 mpg for 230 hp in a 2900lb car is not good, but it's not horrendous.”

Imagine if Mazda used one of their more powerful 4-cylinders. I’m sure the fuel economy would easily reach 30+.

“The upside is that methods for improvement are pretty apparent. Such improvement can come from reshaped combustion chambers (to improve that surface area issue you brought up) direct injection”

It is not possible to reshape the chambers on a rotary engine. Also all present direct injection systems require special pistons. So I do not see how a direct injection system could be implemented on a rotary engine.

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@Phillip

The 16X WILL have direct injection, as Mazda's already announced that, as well as a 40% increase in fuel efficiency. I might be off on the fuel efficiency numbers, but I think they were claiming near 30MPG hwy/city combined.

Yes, everyone has poured some money into Wankel development, but how much has been spent on piston engine development? If you could've invested that same amount of money, you'd have an equal or superior engine, no matter what qualities you compared. I believe it was more of a "if it's not broken, don't fix it" mentality for most of the automotive companies because they knew that re-training mechanics to work on rotaries would cost quite a bit of money, and I'm sure that they didn't want to deal with it if they didn't have to.

Yes, it used to be an emissions nightmare. But reliability? I think you've dealt with too many ricer 3rd gen RX-7 owners who just liked to push the boost on their twin turbos until they blew an apex seal. The rotary is, by design, inherently more reliable than a piston engine. I've seen plenty of rotary engines rebuilt, so I know the internals a bit, and the only parts that would ever have a hard time would be the apex seals, and even those are easy for any person with a 5-gallon bucket to put the engine on to replace (as in, it would be very easy for a mechanic to replace them very cheaply).

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I can see where my words could seem contradictory, but when a company has already spent millions with little results, it gets increasingly difficult for the company to keep investing in what has largely been a black hole. The fact is that the success of an R&D team is based on talent, money, persistance, and luck. Clearly, Mazda was the most persistent, and GM was not as much so. And as much money as GM threw into its rotary program, no amount of funds can make up for the talent of its engineers. I can't say for sure that Mazda's engineers were more talented, but it's a definite possibility.

"Imagine if Mazda used one of their more powerful 4-cylinders. I’m sure the fuel economy would easily reach 30+."

There is definitely an upside in putting the mazdaspeed engine in the RX-8, and frankly, I think that would make it one of the greatest cars of this decade, but one cannot know whether the significantly bigger 4-cylinder would ruin the perfect 50/50 weight distribution and driving dynamics of the RX-8.

As far as reshaping the chambers goes, while the overall shape must remain the same, the center portion can be cut out, shown here:

http://static.howstuffworks.com/gif/rotary-engine-rotor.jpg

yes, it's likely a trade-off between combustion volume and compression ratio, but that shape can be optimized to improve efficiency.

Lastly, another potential improvement can come from using 3 spark plugs per rotor. This would achieve a more complete burn than the current 2-spark system. Mazda has done a 3-spark engine for Le Mans, why not for the road?

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Phillip,my point was that the engine was researched so heavily by so many companies for so many years because it does have advantages. My point was that no one should be critisized for some R&D on an engine that has some of the benefits put forth by a rotary engine.

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