Why Do Rotaries Suck?

[Sydneykid]

Sydneykid, I'd like your opinion on why NOBODY has been able to get an RB series motor into the 6 second bracket or or even close to a 200mph trap speed.

While 2JZ, 13B and 20B powered cars seem to dominate the ANDRA Pro-Turbo class.

I will, if you will give me your opinion on why a 13B at 6.8 litres (that's 3.9 litres x 2 'cause it's a 2 stroke) can't get into the 5's like any decent supercharged 7 litre. Or if you will give me your opinion why a 20B at 11.7 litres (that's 5.85 litres x 2 'cause it's a 2 stroke) can't get into the 4's like any decent Top Fuel engine which is after all only 8.2 litres.

The answer is it's irrelevant, because the engine alone doesn't do 6 seconds or 200 mph, it requires the whole car. And in case you missed it, this thread isn't about chassis, or tyres, or aerodynamics etc, it’s just about engines.

Oh and don’t confuse me with an RB fan boy, they frustrate the hell out of me and I know full well that there are much better engines around, a whole lot of much better engines in fact.

Cheers

Gary

[Parag0n]

20B is 11.7 litres and a 2 stroke, Now I've heard it all.

I wanted your opinion because you seem knowledgeable but honestly you're just taking the piss now.

[ylwgtr2]

EDIT3: Comments re gearbox etc requirements are LAUGHABLE. Same as oil coolers (check out a Mazda RX7 Series 3's oil cooler). The RX8 runs a Mazda MX5 derived gearbox!

yeah....im interested in this aswell as from memory i used the gearbox from my old MA engine in the ute,i just changed the bellhousing....and the gearbox it quite small actually!

[GT-R32]

20B is 11.7 litres and a 2 stroke, Now I've heard it all.

I wanted your opinion because you seem knowledgeable but honestly you're just taking the piss now.

The more he is proven incorrect with his assumptions, the harder he clutches onto them and the wilder they get. It's a reflection of the man and little to do with fact. I would leave it mate.

[ylwgtr2]

Heres a pic of a piston engine with gearbox and beside it is a rotary gearbox......and i think your being a little hard on gary,you will never see things his way and he will never see things your way

[ylwgtr2]

just out of interest....whats sort of 1/4 mile times do guys running honda engines do?

[pixel8r]

One way you can compare all combustion engines that rely on air and fuel in order to turn/rotate a shaft, is to compare how much air and fuel is required for the shaft to be rotating at the same speed in both cases (so long as the shaft is carrying the same load). This is a comparison of efficiency, which to me is far more important than how much power you can make. How much power an engine can make is more a question of money than it is of superiority.

Now before everyone starts comparing 2 engines based on stated capacity, I'm more interested in 2 engines of similar power AND torque (torque being more important) - because this is the only way that you can take LOAD out of the equation. It seems the capacity is largely irrelevant because it all depends on your terminology. And because the engines work differently, a comparison of capacity is meaningless.

In my opinion, an engine with a 2L capacity is the same as an engine with a 1L capacity that "cycles/combusts" twice as fast. So with this in mind, I say capacity is irrelevant. If we're going to talk capacity, we need to talk capacity with respect to time - ie L/min etc.

The reason you cant just use output shaft rpm to compare them is because people could argue all day over whether the 3:1 (or 1:3 whatever way it is) gear in a rotary is a factor. So to remove this out of the equation, and properly compare the efficiencies, you need to assume that both of them are pulling a vehicle with the same gearing and of the same weight. Since we cant physically do that comparison, if we know the engines produce similar power and torque, then thats pretty much the same result.

Obviously I'm talking a lot of theory here, and to compare the efficiency exactly as I've described above is probably not possible, because no direct comparison exists in the real world. The best we can do is pick out cars of similar weight, power and torque and assume that their gear ratios are all the same and then do a comparison of fuel economy. And even then we know that the gear ratios aren't the same so the numbers will still be skewed one way or the other.

So essentially, any comparison between the two is always going to be fraught with problems.

[jame88]

Had to call you up on this one...an RB26DETT has significantly more torque than 314NM.

You are completely correct there, i must have read incorrectly ill edit that.

As for the other many points everyone made,

To be continued...

[mad082]

just out of interest....whats sort of 1/4 mile times do guys running honda engines do?

depends on whether they have v-tak yo

[mad082]

there is one thing that nearly everyone in this thread is forgetting. that is....

that boobs are awesome!!!

[Smity42]

I will, if you will give me your opinion on why a 13B at 6.8 litres (that's 3.9 litres x 2 'cause it's a 2 stroke) can't get into the 5's like any decent supercharged 7 litre. Or if you will give me your opinion why a 20B at 11.7 litres (that's 5.85 litres x 2 'cause it's a 2 stroke) can't get into the 4's like any decent Top Fuel engine which is after all only 8.2 litres.

And once again you are back to doubling the capacity 'because it's a 2 stroke'. Forgetting for a moment that it ISN'T a 2 stroke, can you tell me what the basis is for doubling a 2 stroke's capacity when comparing it to a 4 stroke? Don't just say we double it 'because it's a 2 stroke', but tell me what the reason is that we double a 2 strokes capacity. Then ask yourself, "does the same apply to a rotory?". You will find that it does not.

[Sydneykid]

Gary, you have completely ignored my post, #502. It was quite an amusing explanation of how your "3.9L 2 stroke 6 cyclinder" thing is so incredibly wrong. Instead you claim you are the winner, LOL. It also has a request of you too.

Is that the sounds, I was going to leave it until I could listen to them on a decent sound system. Which I will do when I can, but I think you may have missed the most important comparison point, is the 6 cylinder 3.9 litre 2 stroke piston engine only doing 3,000 rpm? Because if it's doing more rpm then there is no wonder it doesn't sound like a 3.9 litre rotary only doing 3,000 rpm.

BTW everyone, we all need to ignore NM according to Gary (yet he mentions it?), as they are measured at the output shaft which is entirely irrelevant to everything. Instead we look at rotor cycles to draw relatives.

You know that's not what I said, but if it makes you feel good, then go for it.

EDIT: Phil Irving loves talking about various things relative to crank degrees, something Gary ignores or doesn't understand with his 3.9L 2 stroke calls (which are wrong), eg:

I understand, I have my reasons for the actual capacity and Phil had his. So yes, we used totally different methodology of arriving at pretty much the same capacity. I'm not sure how that supports your argument when 2 quite different methods arrive at pretty much the same conclusion, that Mazdas claimed capacity is out by a long, long, long way.

EDIT2: There are plenty of FWD rotaries.

Well I've seen a few guys have a go at sticking rotaries in FWD cars, not much of success, for the obvious reasons that they are too heavy and hard to fit. But car manufacturers with actual main stream models? I actually can't think of one made in the last 5 years. Or even one made this century, let alone one in the last 20 years, or 30 years. From memory the NSU R80 started in 1968 and lasted (sort of) until 1977. So I would have trouble naming one designed even in the last 40 years.

EDIT3: Comments re gearbox etc requirements are LAUGHABLE. Same as oil coolers (check out a Mazda RX7 Series 3's oil cooler). The RX8 runs a Mazda MX5 derived gearbox!

So what Mazda FWD car needs an oil cooler?

The MX5 is a RWD isn't it.

Any counter 'arguments' set out by Gary remit vital information and contain the assumption, by him, that he is correct. It's borderlline childish, but really reflects self concept. I'm still waiting for my reply to post #502.

I certainly do remit vital information, but you omit it when it doesn't align with your argument.

Cheers

Gary

[Sydneykid]

And once again you are back to doubling the capacity 'because it's a 2 stroke'. Forgetting for a moment that it ISN'T a 2 stroke, can you tell me what the basis is for doubling a 2 stroke's capacity when comparing it to a 4 stroke? Don't just say we double it 'because it's a 2 stroke', but tell me what the reason is that we double a 2 strokes capacity. Then ask yourself, "does the same apply to a rotory?". You will find that it does not.

Oh come on, a 13B rotary combusts/fires 6 times in one complete cycle of it's rotors, irrefutable fact. Whereas a piston 4 stroke 6 cylinder would only combust/fire 3 times in one complete cycle of it's pistons. So it produces double the power of a 4 stroke because it has double the number of combustion process in one cysle, ineficiencies notwithstanding.

Cheers

Gary

[Parag0n]

Well I've seen a few guys have a go at sticking rotaries in FWD cars, not much of success, for the obvious reasons that they are too heavy and hard to fit. But car manufacturers with actual main stream models? I actually can't think of one made in the last 5 years. Or even one made this century, let alone one in the last 20 years, or 30 years. From memory the NSU R80 started in 1968 and lasted (sort of) until 1977. So I would have trouble naming one designed even in the last 40 years.

Cheers

Gary

Mazda Luce 1969-1972

13A two 655 cc rotors.

Clutching at straws maybe but they were indeed used in a mass produced FWD car.

Edited September 29, 2009 by Parag0n

[jame88]

OK well i'll start with the speed argument.

Heres the animation posted earlier in this thread, also on wikipedia

I can see where many of you may how got confused here. There is indeed a ring/pinion gearset which has a 3:1 ratio in the Wankel engine. The ring gear is attached to the inside of the rotor, but where you seem to have misunderstood is the pinion gear is FIXED to the rotor housing. NO POWER is transmitted through this gearset. This gearset's only purpose is to force the rotor to move in a Wankel cycle.

All power is transmitted from the rotor to the eccentric shaft via bearings on the lobes of the eccentric shaft (the white circle in the center of the rotor in the animation).

You are correct in that the rotor is rotating about its center (point A rotating about point B) at 3000rpm when the engine speed is 9000rpm. This is however about as relevant as the speed in rpm of the camshaft, timing chain, water pump etc in a piston engine, as no power is produced at the output shaft of the engine from this rotation.

Power is produced in a Wankel from the rotation of the center of the rotor (point B) about the centre of the output shaft. This rotation is at 9000rpm and should be where the speed of the rotors in taken from.

This is an eccentric shaft for a 13b engine, notice the offset lobes which the rotor rotates on, and the lack of gears of the shaft.

Hopefully i have explained this better and those of you who care to learn will benefit.

As for the other debates (combustion cycle, capacity etc) i will explain these further when i have a chance, as there is only so many hours in a day.

[Sydneykid]

20B is 11.7 litres and a 2 stroke, Now I've heard it all.

I wanted your opinion because you seem knowledgeable but honestly you're just taking the piss now.

Yes I am, but I believe I have good reason. The rotary huggers want to divide the true rotary engine capacity by 3 because of a step up ratio. So, in retaliation, I double the capacity because it's a 2 stroke. In truth I don't dived or multiply an engine's capacity by anything, what it pumps is what capacity it is.

If you want a truthfull answer then it's obvious, there is no category advantage for 3.9 litre 6 cylinder piston engines like there is for 13B rotaries, so no one bothers building them. Ditto 5.85 litre piston engines like there is for 20B rotaries, so no one bothers.

Cheers

Gary

[Sydneykid]

just out of interest....whats sort of 1/4 mile times do guys running honda engines do?

I seem to recall Stephan Papadakis from AEM Racing doing a 7+ for a FWD at ~180 mph and a RWD 6+ at ~200 mph.

Cheers

Gary

[ylwgtr2]

Mazda Luce 1969-1972

13A two 655 cc rotors.

Clutching at straws maybe but they were indeed used in a mass produced FWD car.

It certainly is clutching at straws...they made 976...hardly mass produced

[Parag0n]

Hey, Gary just wanted to know if they were ever made in the last century, I helped him out with the car name.

But yes they are rare.

[Sydneykid]

OK well i'll start with the speed argument.

Heres the animation posted earlier in this thread, also on wikipedia

I can see where many of you may how got confused here. There is indeed a ring/pinion gearset which has a 3:1 ratio in the Wankel engine. The ring gear is attached to the inside of the rotor, but where you seem to have misunderstood is the pinion gear is FIXED to the rotor housing. NO POWER is transmitted through this gearset. This gearset's only purpose is to force the rotor to move in a Wankel cycle.

All power is transmitted from the rotor to the eccentric shaft via bearings on the lobes of the eccentric shaft (the white circle in the center of the rotor in the animation).

You are correct in that the rotor is rotating about its center (point A rotating about point B) at 3000rpm when the engine speed is 9000rpm.

This is however about as relevant as the speed in rpm of the camshaft, timing chain, water pump etc in a piston engine, as no power is produced at the output shaft of the engine from this rotation.

Power is produced in a Wankel from the rotation of the center of the rotor (point B) about the centre of the output shaft. This rotation is at 9000rpm and should be where the speed of the rotors in taken from.

This is an eccentric shaft for a 13b engine, notice the offset lobes which the rotor rotates on, and the lack of gears of the shaft.

Hopefully i have explained this better and those of you who care to learn will benefit.

As for the other debates (combustion cycle, capacity etc) i will explain these further when i have a chance, as there is only so many hours in a day.

Hang on, so the outside of the rotor does 3,000 rpm but the inside does 9,000 rpm, That's a good trick, but I some how doubt it. The fact is the whole rotor is doing 3,000 rpm, and the rotor is the combustion medium, it's what makes the power, somewhat like a piston in a piston engine in that regard. So comparing it to a water pump is pretty stupid, they don't produce any power. Nice try on muddying the water with the camshaft rpm, but that's a 4 stroke. How about we compare it with a 2 stroke piston engine with no valves (like a rotary) and no camshafts (also like a rotary). Bingo, everything is doing 9,000 rpm (or cpm if you prefer) but in a rotary, oops the main parts, the bits that make the power, the rotors, are only doing 3,000 rpm (or opm if you prefer).

Why do I feel like I have answered this all before? Maybe because I have.

The simple truth is what the eccentric shaft lobes do is to convert the 2 styles of kinetic energy of a rotor, the rotate and the orbit, into one style of kynetic energy, the round and round rotation of the eccentric shaft itself. There is no magic here, it's much like the the throw of a crankshaft converts the up and the down of a piston into the round and round rotation of the crankshaft itself.

Cheers

Gary