Why Do Rotaries Suck?

[Sydneykid]

Actually an Automotive Engineer would be.

What capacity does an Automotive Engineer attribute to a 2 litre 2 stroke piston engine? Last time I checked my reference books they said 2 litres.

What capacity does an Automotive Engineer attribute to a 2 litre 4 stroke piston engine? Last time I checked my reference books they said 2 litres.

So my Automotive Engineering references all ignore the number of revolutions of the cranskshaft when determining the relative capacities of 2 and 4 stroke piston engines.

In simple terms they are both 2 litre engines.

I see no reason to not follow exactly the same logic when measuring the capacity of a rotary. So I ignore the number of revolutions of the eccentric shaft when determining the capacity of a rotary.

To do otherwise would be illogical, inconsistent and just plain wrong.

Cheers

Gary

[Sydneykid]

From thin air I hear.

No it based on the manufacturers specifications.

Mazda (they are the manufacturer) quotes 1.3 litres for a 13B, they don't multiply it by anything.

Cheers

Gary

[Sydneykid]

How do CAMS get to their 1.8 multiplier of Mazda's rating?

I don't know exactly how the 1.8 times was calculated. I do know it used to be to be 2 times some years ago. But the ACO (the organisers of the LeMans 24 Hour) rejected the 2 times multiplier as not being enough, that's why no rotaries running there any more. So even the motorsport regulators of the world can't agree on a multiplier.

Whilst they don't agree on a multiplier it is unanimous that the Mazda quoted 1.3 litres for a 13B is wrong as a comparitor. The argument is really all about how wrong it is. The 1.3 litre lie was exposed long ago.

Cheers

Gary

[Sydneykid]

Mmmm I think the only way to accurately compare the wankel with a 4 stroke would be to compare cfm @ ?? rpm (rpm measured at the rotor).... for efficiency.

1 full combustion cycle with every 3 turns of the crank (or full cycle of the rotars).

Done it, the ariflow meter reads around 3.1 litres, that being 3.9 litres at around 80% efficiency.

Cheers

Gary

[madbung]

Sounds about right, that'd be the way I'd go about.

[Sydneykid]

Not at all. You'd have to be a pedantic bastard to actually give a shit that some ignorant fellow might think 1.3 litres worth of rotary is the same as 1.3 litres worth of piston 4 stroke.

So you think everybody who believes Mazda's claim of 1.3 litres for a 13B is an "ignorant fellow"? That's a bit harsh isn't it?

Personally I believe that some people actually believe that Mazda wouldn't lie, hence the 1.3 litres must be right. They're not ignorant, just tricked by the Mazda marketing spin. All I am trying to do is open their eyes to the possibility that maybe they have been conned. If you want to call me a "pedantic bastard" for exposing them to the truth, then so be it.

Cheers

Gary

[madbung]

Gary, out of curiousity did you cfm a comparable piston engine?

If so what was it's efficiency.

[gts-t 32]

they go bang nicely.

[Birds]

So you think everybody who believes Mazda's claim of 1.3 litres for a 13B is an "ignorant fellow"? That's a bit harsh isn't it?

Personally I believe that some people actually believe that Mazda wouldn't lie, hence the 1.3 litres must be right. They're not ignorant, just tricked by the Mazda marketing spin. All I am trying to do is open their eyes to the possibility that maybe they have been conned. If you want to call me a "pedantic bastard" for exposing them to the truth, then so be it.

Cheers

Gary

How is it not ignorant to ignore (key word) the fact that Mazda refer to their 1.3 litre engine as a rotary...and not find out for yourself why it is called a rotary in the first place. Everyone in this thread debating these points knows how the rotary works, and even if they don't know how it works, they all acknowledge that it is nowhere near the same as a 1.3 litre 4 stroke piston engine and therefore should not be classed as such. You don't have to look hard to find this information at all and you never did. Hell, if a Mazda salesman had half a brain he'd have been able to explain the basics of it to you on the showroom floor. I'm sure the question got asked of them more than a few times. Your claims that people were conned by Mazda...I see it as no different to someone who has only known 4 strokes their whole life, viewing a 2 stroke engine that is labelled the same displacement as a 4 stroke engine and assuming that they will both have similar performance and fuel economy. But how very wrong they would be in making this assumption, just like anyone who ever assumed the same about a 1.3 litre rotary. What good is engine displacement to your knowledge if you don't know the context within which the term is being used? Ignorance is no excuse for trying to judge an engine on its parameters without actually knowing how the thing operates. If Mazda want to take advantage of this ignorance...that is NOT lying, that's called marketing and every manufacturer does it. The same goes for people assuming a turbocharged 2 litre will give you the same performance as a naturally aspirated 2 litre - if it wasn't for the generic pop culture use of the word "turbocharged", only those who knew what turbocharging actually does for an engine would be the wiser about it. While we're at it, let's include diesel engines in our list of ignorant assumptions that average joe might make: 'them 4.2 litre diesels must make more power and guzzle more gas than a 3 litre petrol engine...just look at the displacement difference between them'. Fail. Is that Toyotas fault for not explaining to the customer how a diesel engine differs from a petrol...besides which pump you use to fill it up at the servo?

And like I said before, the supposed lies stop at the brochures...once someone drives the car and sees the fuel economy it or performance it has to offer, do you think even the most ignorant of "fellows" will still view this engine as equivalent to a 1.3 litre 4 stroke piston engine? Everyone knows the 1.3 litre rotary is a thirsty and powerful engine. Mazda didn't get away with anything they didn't deserve to get away with.

And yes, I still think you're a pedantic bastard, a hypocritical one at that...because you nazi terms like "displacement" to have an exact definition and method of measurement whilst loosely using other terms like revolutions per minute and claiming it to be narrow minded / pedantic should someone want to clarify these with a specific definition, when they actually have one!

[Jez13]

What capacity does an Automotive Engineer attribute to a 2 litre 2 stroke piston engine? Last time I checked my reference books they said 2 litres.

What capacity does an Automotive Engineer attribute to a 2 litre 4 stroke piston engine? Last time I checked my reference books they said 2 litres.

So my Automotive Engineering references all ignore the number of revolutions of the cranskshaft when determining the relative capacities of 2 and 4 stroke piston engines.

In simple terms they are both 2 litre engines.

I see no reason to not follow exactly the same logic when measuring the capacity of a rotary. So I ignore the number of revolutions of the eccentric shaft when determining the capacity of a rotary.

To do otherwise would be illogical, inconsistent and just plain wrong.

Cheers

Gary

There is one reason why I feel we cant apply the same logic. This is because one rotor holds 3 (4) chambers of air but only combusts one at a time, so it only expels 1.3l of air/exhaust per combustion. One piston holds the same amount of air and combusts that same amount of air per cycle. The rotor holds 3.9l of air but only combusts 1.3l per combustion (1:1 as opposed to 3:1).

[Sydneykid]

Gary, out of curiousity did you cfm a comparable piston engine?

If so what was it's efficiency.

A current generation, say Honda F20 or K20 are close to 90% brand new and after run in around 93%. As a comparison for a race engine, a V8SuperCar engine (pushrod V8) is ~96% as measured on the engine dyno after run in.

Cheers

Gary

[Birds]

There is one reason why I feel we cant apply the same logic. This is because one rotor holds 3 (4) chambers of air but only combusts one at a time, so it only expels 1.3l of air/exhaust per combustion. One piston holds the same amount of air and combusts that same amount of air per cycle. The rotor holds 3.9l of air but only combusts 1.3l per combustion (1:1 as opposed to 3:1).

Well, to be fair, a 2 litre 4 cylinder piston engine will only combust 1/4 of its total displacement (500cc) in each cylinder and they don't all combust at once either.

But yes, you can look at a rotor as a single cylinder, in which case you can work out displacement for a rotary as the sum of one combustion chamber on each rotor. One thing that supports this idea is that only 2 chambers in a twin rotor engine have spark plugs in them...as opposed to a 6 cylinder piston engine which has 6 chambers with a spark plug in each. It's very subjective as far as what displacement you want to give this engine...hence this thread is so long. But once again, comparing pistons with rotaries based on their internal combustion mediums is pretty stupid. The only way to compare these engines, if you do, is to compare their inputs and their outputs. The in between is irrelevant because beyond the physics and chemistry of internal combustion, they share nothing in common.

[GT-R32]

A current generation, say Honda F20 or K20 are close to 90% brand new and after run in around 93%. As a comparison for a race engine, a V8SuperCar engine (pushrod V8) is ~96% as measured on the engine dyno after run in.

Cheers

Gary

Now you're getting close to why CAMS run a x1.8 of Mazda's rating. Or perhaps it should be a x0.59 of 'your' rating instead?

[Sydneykid]

There is one reason why I feel we cant apply the same logic. This is because one rotor holds 3 (4) chambers of air but only combusts one at a time, so it only expels 1.3l of air/exhaust per combustion. One piston holds the same amount of air and combusts that same amount of air per cycle. The rotor holds 3.9l of air but only combusts 1.3l per combustion (1:1 as opposed to 3:1).

Say what? Let's apply the same logic to a a 3.9 litre 6 cilinder piston engine. It has 6 chambers of air but only combusts one at a time, so it only expels 650 cc of air/exhaust per combustion. So we should call it a 650 cc engine, I don't think so.

If you want to do the comparion the 3.9 litre 6 cilinder piston engine will need 2 revolutions of its cranksahft to expel 3.9 litres of air/exhaust. While a 3.9 litre 6 chamber rotary engine will need 3 revolutions of its eccentric shaft to expel 3.9 litres of air/exhaust

We don't dived the 3.9 litre 6 cilinder piston engine's capacity by 2, so why should we divide a 3.9 litre 6 chamber rotary engine's capacity by 3?

Any way you look at it it's wrong, it's illogical, it's inconsistent and it's a flat out lie to cal a a 3.9 litre 6 chamber rotary engine a 1.3 litre rotary engine.

Cheers

Gary

[Sydneykid]

Now you're getting close to why CAMS run a x1.8 of Mazda's rating. Or perhaps it should be a x0.59 of 'your' rating instead?

Oh so now we use effeicieny to determine an engine's capacity. So if I have a 3.9 litre 6 that a bit tired and only pumps 70% I get to call it a 2.7 litre. That's makes a lot of sense, so if I build sloppy engines with poor pumping efficiency I get to run in a lower capacity class. We both know that's not how it works, it's still a 3.9 litre engine no matter how efficient or ineficient it is and that's what it classified as.

Using your logic a Renesis engine should have a larger capacity rating as it is more efficient.

Cheers

Gary

[GT-R32]

Oh so now we use effeicieny to determine an engine's capacity. So if I have a 3.9 litre 6 that a bit tired and only pumps 70% I get to call it a 2.7 litre. That's makes a lot of sense, so if I build sloppy engines with poor pumping efficiency I get to run in a lower capacity class. We both know that's not how it works, it's still a 3.9 litre engine no matter how efficient or ineficient it is and that's what it classified as.

Using your logic a Renesis engine should have a larger capacity rating as it is more efficient.

Cheers

Gary

So you don't know why CAMS use a x1.8? Equivalent to x0.59 of your (3.9L for the 13B) rating. Weird for someone so interested in this and is self reportedly high up the food chain.

[Jez13]

Say what? Let's apply the same logic to a a 3.9 litre 6 cilinder piston engine. It has 6 chambers of air but only combusts one at a time, so it only expels 650 cc of air/exhaust per combustion. So we should call it a 650 cc engine, I don't think so.

If you want to do the comparion the 3.9 litre 6 cilinder piston engine will need 2 revolutions of its cranksahft to expel 3.9 litres of air/exhaust. While a 3.9 litre 6 chamber rotary engine will need 3 revolutions of its eccentric shaft to expel 3.9 litres of air/exhaust

We don't dived the 3.9 litre 6 cilinder piston engine's capacity by 2, so why should we divide a 3.9 litre 6 chamber rotary engine's capacity by 3?

Any way you look at it it's wrong, it's illogical, it's inconsistent and it's a flat out lie to cal a a 3.9 litre 6 chamber rotary engine a 1.3 litre rotary engine.

Cheers

Gary

No I dont want to compare a 6 cylinder piston engine to a rotory because the piston engine gets combustions and outlets from six different places at different times. A rotory has only has 2 outlets (ports). They are not suitable for comparison.

This guy here explains it:

He explains that 3 combustion cycles make 3 turns of the e/shaft. Not one cycle for 3 turns of the e/shaft.

[GT-R32]

Jez you are basically explaining why a 20B gives of a resonance similar to an inline six cylinder.

Gary, on the other hand, believes a 13B @ 9000RPM sounds like a 6 cylinder @ 3000RPM.

[DRD-00F]

Moot point GT-R32, sound has VERY little to do with any of this (I just might know a thing or two about sound).

The 1980 Mazda RX-7 GS

Just one look is all if takes to appreciate the exceptional value of the Mazda RX-7 versus Datsun 280ZX or Porsche 924.

As remarkable as the Mazda RX-7 is on its own merits, it looks all the better when compared with the competition. Because the sleek, aerodynamic RX-7 is virtually everything you could want in a refined sports car—at an almost unbelievable price.

It can reach 0-50 in 6.3 seconds. Its inherently compact rotary engine is placed behind the front axle, for ideal weight distribution and superb handling.

In auto racing, a specially prepared RX-7 won its class at the Daytona 24-hour race. Another RX-7 set a world speed record at Bonneville.

The smoothness of the rotary engine makes the RX-7 a quiet sports car. All this performance from a car that can attain excellent gas mileage on the open road.

17 EST.mpg 28 EST.** hwy mpg

But the front mid-engine RX-7 offers infinitely more than performance. It also provides extraordinary comfort.

So if you know what you want in a sports car, and you don’t want to pay a king’s ransom to get it, take a look at the RX-7 GS or S Model. The beautifully-styled, high-mileage, high-performance sports cars from Mazda.

You’re also going to like the looks of RX-7 GS standard features.

AM/FM stereo radio with power antenna • Side-window demisters Cut-pile carpeting Tinted glass • 5-speed • Tachometer • Styled steel wheels • Steel-belted radial tires Front and rear stabilizer bars • Ventilated front disc and finned rear drum brakes with power assist • Electric remote hatch release. 3-speed automatic transmission, air conditioning, aluminum wheels and sun roof available as options.

$8295 *

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**EPA estimates for comparison purposes for GS Model with 5-spd. Trans. The mileage you get may vary depending on how fast you drive, the weather, and trip length. The actual highway mileage will probably be less. California, 16 estimated mpg, 27 estimated highway mpg.

Mazda’s rotary engine licensed by NSU-WANKEL

MAZDA (logo)

The more you look, the more you like.

Found this kinda funny quite inherent of the advertising we've been discussing from Mazda...

[GT-R32]

Elaborate DRDOOF. You can't just say that and not explain yourself.