Why Do Rotaries Suck?

[Sydneykid]

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!

The problem with your examples is that in each of them the engine manufacturer is quoting the actual capacity of the engine, a 1.3 litre 4 stroke piston engine is called a 1.3 litre, a 3 litre 2 stroke petrol engine is called a 3 litre, a 4.2 litre diesel engine is called a 4.2 litre. That capacity is measured by how much they pump in one complete cycle of their combustion media. Except one, Mazda call a 3.9 litre rotary engine a 1.3 litre.

Yes of course there are differences in how an engine performs depending on it's type, diesel, petrol 2 stroke or 4 stroke and that why the engine manufactuer tells us what type of engine it is, so we know what to expect. But they don't lie about the actual capacity, they don't halve it cause it's a 4 stroke, they don't double it cause it's a 2 stoke. But not Mazda, they divide the actual capacity by 3.

I don't believe that I am being pedantic in believing that all engines should state their true capacity.

Cheers

Gary

[madbung]

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

Thx Gary, that really shows the downside of it's design.....Although capable of large hp it doesn't achieve the result as efficiently as the piston engine. it's just can't pump the same volume as efficiently even with centralized ports.

Not much fun when the medium is $1.50ltr

That's all I wanted to know, Thx.

[DRD-00F]

Audio as a characteristic is defined by the space it takes up and the objects that interfer with it. This is why you use a certain literage for a subwoofer, paired with a decent, solid wood that won't reverberate too much. When you have an engine like a rotary, trying to compare it in audio only to that of a piston car, there are way too many differentiating variables to make a clear account. The combustion chambers are a different size/shape/material, the combustion itself is of a different size, the walls of the combustion chambers are a different size/shape/MOVING in one of them... From an audio point of view, this is probably as good as comparing a subwoofer to a drum. Everything except for 2 things are different. The type of sound they are trying to make, and the frequencies it can create.

I can guarentee that the only thing simliar that you are hearing is the frequency.

Don't even get me started on exhausts.

[GT-R32]

I understand. But the basis of the sound is combustion. Why do V8s sound similar? 4s? 6s? Sure, there are variables that can produce a different note for each, but by and large the combustion, how and when it occurs, produces noticeable similarities. You are talking fine difference I am talking basis of the pattern of sound.

[Sydneykid]

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.

OK, so a Mini (BMC not BMW) engine has siamesed exhaust ports for it centre 2 cyliders ie; 3 exhaust ports for 4 cylinders. That means we should only count 75% of it's capacity. But we don't.

A rotary engine takes 3 turns of it's eccentric shaft and Mazds divide it by 3. A 4 stroke piston engine takes 2 turns of its crankshaft, so we should dived its capacity by 2. But we don't.

Cheers

Gary

[GT-R32]

Still awaiting reply to post #657 Gary.

[DRD-00F]

Pretend you have Playdo. A maluable medium. Then you squish it through 2 different pipes, shapes etc. Yes, it will still come out as playdo, and as much as you put in, the same amount will come out, but it will be completely different in every other aspect.

Playdo is combustion.

PS: "pattern of sound" is frequency, like I said. While yes it is important, it's not really going to prove anything except for similar combustion times.

[GT-R32]

PS: "pattern of sound" is frequency, like I said. While yes it is important, it's not really going to prove anything except for similar combustion times.

PS: That's precisely what I was on about.

[DRD-00F]

So it's varied by the rpm. Great. What does that prove?

PPS: real world comparisons won't be anything great, as a 6 cylinder will fire 3 times in 360 degrees while an 8 cylinder will fire 4 times, and a 13B will fire twice (? twin rotor and all, could be wrong).

[Sydneykid]

I understand. But the basis of the sound is combustion. Why do V8s sound similar? 4s?

But they don't, the firing order has a large efect on the sound. That's why a Ford V8 doesn't sound the same as Chevy V8.

6s?

Obviously a V6 doesn't sound anything like a I6.

Sure, there are variables that can produce a different note for each, but by and large the combustion, how and when it occurs, produces noticeable similarities. You are talking fine difference I am talking basis of the pattern of sound.

A Renesis engine, because of its port layout, sounds quite different.

The number/time of combustion/exhaust events also influences the sound of an engine a lot. We have a V8 SuperCar engine Windsor (5 litre) that has had a longer stroke crank fitted (6 litres) which means slightly higher gudgeon pin height in the pistons. Everything else is exactly the same, but the sound is very different.

Even the same engine can sound quite different, say a VTEC Honda on the low lift short duration camshaft lobes, it sounds completely different on the high lift long duration lobes.

Cheers

Gary

[ylwgtr2]

Im still waiting on an answer for this......

i have a CR500 two stroke engine here which the manufacture claims 491cc...it bore and stroke is 89mmx79mm...its exhaust port closes at around 47mm from TDC....i feel robbed of 32mm of combusting stroke and 198.61cc's:(

[DRD-00F]

That's not even a question...

[ylwgtr2]

it is if we are measuring and engine by its combustion for its own cycle

[Birds]

The problem with your examples is that in each of them the engine manufacturer is quoting the actual capacity of the engine, a 1.3 litre 4 stroke piston engine is called a 1.3 litre, a 3 litre 2 stroke petrol engine is called a 3 litre, a 4.2 litre diesel engine is called a 4.2 litre. That capacity is measured by how much they pump in one complete cycle of their combustion media. Except one, Mazda call a 3.9 litre rotary engine a 1.3 litre.

Yes of course there are differences in how an engine performs depending on it's type, diesel, petrol 2 stroke or 4 stroke and that why the engine manufactuer tells us what type of engine it is, so we know what to expect. But they don't lie about the actual capacity, they don't halve it cause it's a 4 stroke, they don't double it cause it's a 2 stoke. But not Mazda, they divide the actual capacity by 3.

I don't believe that I am being pedantic in believing that all engines should state their true capacity.

Cheers

Gary

You're still completely missing the point that the manufacturer quoted displacement figure is irrelevant as long as it is consistent with our knowledge of rotaries. Why do you ignore this? You are so adamant about this engine being labelled 3.9 litres that you're missing the pragmatics of it. With knowledge of how a rotary works we know EXACTLY where Mazda get their 1.3 litres from...we know that this displacement is based on a single chamber of each rotor. This information was always available to someone who knew what a rotary was about. How can it possibly be lying, when Mazda (as you say, the only mainstream manfacturer who successfully adopted the engine, and continue to use it) have maintained the same displacement measurement across all rotary engines for years and years? It might be different if there were other manufacturers who produce an equivalent 13B engine and class it as a 3.9 litre...because then one of these manufacturers claims would be inconsistent with the other...and therefore we can call bullshit on someone. But given we only have one manufacturer producing mainstream rotaries...they can set the template for how rotary engine capacity is measured. Whatever science or comparison to existing piston engines you want to throw at it, are completely irrelevant.

You are pedantic. Given you're the only one in this thread...out of all the people here that understand how a rotary works...who has a hate on for the way Mazda define their engine...I think I can get away with saying you are pedantic.

[NZM.031]

does it not have alot to do with exhaust manifolds and pipe length?? like a wrx with stock manifolds sounds like a lumpy rex... but put some equal length extractors on it and it sounds close to a a normal inline 2L 4 cyl.... ahh forget it, im not getting involved.

[ylwgtr2]

does it not have alot to do with exhaust manifolds and pipe length?? like a wrx with stock manifolds sounds like a lumpy rex... but put some equal length extractors on it and it sounds close to a a normal inline 2L 4 cyl.... ahh forget it, im not getting involved.

i could make my mums laser sound like a wrx by pulling one of the spark plug leads off

[Sydneykid]

So you don't know why CAMS use a x1.8?

The mathematics of exactly why 1.8 times was chosen, instead of say 1.9 or 1.7 or leaving it at 2, no I don't know. It was a bit of a closed shop back then, that secret boys club stuff is why there was a big spill in the CAMS board, new president etc.

I don't recall an official communication on it, there was some discussion that it may have been pushed due to improvemetns in piston engine efficiency in the previous 25 years compared to virtuallty static rotary rotary efficiency. If we knew that for a fact, which we don't, then a counter argument could be made based on Renesis development. In simple terms, there has been rotary development, put it back to 2 times.

Personally 1.8 or 2.0 is irrlevant as it is simply a multiplier of a number that is incorrect anyway. ie; 2.0 X wrong = wrong.

Equivalent to x0.59 of your (3.9L for the 13B) rating.

Never expressed it as 0.59, let me check, 1.3 x 1.8 = 2.35 / 3.9 = 0.59.

Yep, the maths works, but I have idea what 0.59 means.

Is there some signifiicance to 0.59?

Weird for someone so interested in this and is self reportedly high up the food chain.

I know that it was reduced from 2 times in the mid 90's, I can't remember the exact year, I'd have to check my CAMS Manuals. Different food chain back then. I know that it's now 1.8 times, but only in Australia, it is different elsewhere. A turbo petrol engine is 1.7 times and a turbo diesel will be 1.5 times when CAMS approves my recommendation on it.

Cheers

Gary

[Jez13]

OK, so a Mini (BMC not BMW) engine has siamesed exhaust ports for it centre 2 cyliders ie; 3 exhaust ports for 4 cylinders. That means we should only count 75% of it's capacity. But we don't.

A rotary engine takes 3 turns of it's eccentric shaft and Mazds divide it by 3. A 4 stroke piston engine takes 2 turns of its crankshaft, so we should dived its capacity by 2. But we don't.

Cheers

Gary

Because your comparing a piston engine again. Each piston makes one combustion per cylinder where a rotory makes 3 per rotor.

[Sydneykid]

You're still completely missing the point that the manufacturer quoted displacement figure is irrelevant as long as it is consistent with our knowledge of rotaries. Why do you ignore this? You are so adamant about this engine being labelled 3.9 litres that you're missing the pragmatics of it. With knowledge of how a rotary works we know EXACTLY where Mazda get their 1.3 litres from...we know that this displacement is based on a single chamber of each rotor. This information was always available to someone who knew what a rotary was about. How can it possibly be lying, when Mazda (as you say, the only mainstream manfacturer who successfully adopted the engine, and continue to use it) have maintained the same displacement measurement across all rotary engines for years and years? It might be different if there were other manufacturers who produce an equivalent 13B engine and class it as a 3.9 litre...because then one of these manufacturers claims would be inconsistent with the other...and therefore we can call bullshit on someone. But given we only have one manufacturer producing mainstream rotaries...they can set the template for how rotary engine capacity is measured. Whatever science or comparison to existing piston engines you want to throw at it, are completely irrelevant.

You are pedantic. Given you're the only one in this thread...out of all the people here that understand how a rotary works...who has a hate on for the way Mazda define their engine...I think I can get away with saying you are pedantic.

To me it's black and white, a rotary is a combustion engine, Otto cycle if you prefer. All other combustion engines, every single one of them, are measured the same way. Piston port, 2 stroke, 4 stroke, diesel, petrol, 2 valves, 4 valves, 5 valves, pushrod, SOHC, DOHC etc etc they are all measured exactly the same way. Regardless of efficiency or number of revolutions of the crank/eccentric shaft. There is only one that isn't and that's wrong.

You say Mazda should be allowed to get away with it becuase they say its "1.3 litre rotary engine", the "rotary" qualifier means they can use whatever measuring stick they like. But if anyone else tried the "1.3 litre 4 stroke" or "1.8 litre diesel" when it was really a 2.6 litre you'd be screaming blue murder.

You say it's OK to understate the engine's true capacity by a factor of 3, because everyone knows its really a 3.9 litre. When the truth is not everyone knows, this thread is living proof of that. If everyone knew then it would have stopped at page 1.

I have plenty more ways of explaining why 1.3 litres is wrong, using any termninology you care to dream up. You can muddy the water all you like, I know what the bottom of the river looks like and I can clear it up so everyone else can see it too.

Cheers

Gary

[DRD-00F]

You're still completely missing the point that the manufacturer quoted displacement figure is irrelevant as long as it is consistent with our knowledge of rotaries. Why do you ignore this? You are so adamant about this engine being labelled 3.9 litres that you're missing the pragmatics of it. With knowledge of how a rotary works we know EXACTLY where Mazda get their 1.3 litres from...we know that this displacement is based on a single chamber of each rotor. This information was always available to someone who knew what a rotary was about. How can it possibly be lying, when Mazda (as you say, the only mainstream manfacturer who successfully adopted the engine, and continue to use it) have maintained the same displacement measurement across all rotary engines for years and years? It might be different if there were other manufacturers who produce an equivalent 13B engine and class it as a 3.9 litre...because then one of these manufacturers claims would be inconsistent with the other...and therefore we can call bullshit on someone. But given we only have one manufacturer producing mainstream rotaries...they can set the template for how rotary engine capacity is measured. Whatever science or comparison to existing piston engines you want to throw at it, are completely irrelevant.

You are pedantic. Given you're the only one in this thread...out of all the people here that understand how a rotary works...who has a hate on for the way Mazda define their engine...I think I can get away with saying you are pedantic.

What if you have NO knowledge of a rotary (believe it or not birds, this is most of the world)? What if Mazda DID already compare this engine/car combo with existing piston engined cars?

It's, at best, tricky, underhanded advertising, and at worst, a lie.

SHOES SHOES SHOES! BUY TWO, GET ONE FREE!

Would you expect to walk out of the store with 3 shoes, or 3 pairs?

Mazda aren't stupid, they knew exactly what they were doing, and I for one, don't agree with those tactics.

does it not have alot to do with exhaust manifolds and pipe length?? like a wrx with stock manifolds sounds like a lumpy rex... but put some equal length extractors on it and it sounds close to a a normal inline 2L 4 cyl.... ahh forget it, im not getting involved.

Yes it does, but I said don't get me started on exhausts!