7.06 at 193mph in a 1.3 litre

JamesMcD wrote: I'm going to start an argument, but... It's 2.6 liters

No. Just because the rotary is smarter and is essentially a 1-stroke does not mean you get to arbitrarily assume it has double the displacement available for ONE power revolution, which is how displacement is measured.

If you want to call a 13B a 1.3 liter, that's fine if you are doing so for the purpose of comparing it to other rotary engines. But if you are making a comparison to a piston engine, you have to double the displacement figure if your goal is to make a meaningful apples to apples comparison.

Here is the reason:

A single-cylinder piston engine only makes power on 1 out of 2 rotations of the output shaft. The first rotation is suck/squish, the second is bang/blow. You don't get any power out of suck/squish, so power is being transmitted every other rotation.

Now on a single-rotor wankel engine, there is a combustion event on every rotation of the output shaft. Power is being transmitted every time the shaft goes around.

So, to make an apples to apples comparison between pistons and rotaries, you need to acknowledge that the wankel is "exercising its displacement" twice as often as the piston engine, and thus the correct thing to do is to speak of a 13b, "1.3 liter" rotary as being a 2.6.

Let's look at this experiment I just did. I happened to have these parts sitting around:

Here is 1.3 liters of fluid (I have always thought that displacement was green):

Here we see that 1/2 of the 1.3 liters fits in the combustion space at BDC:

So you might think "aha, it's a 2 rotor engine so that makes it a 1.3 liter!" Yes, the displacement total is 1.3 liters, but because the rotary burns fuel twice as fast as a piston engine, and transmits power twice as often, we have to call it a 2.6 liter if comparisons are to be made with the world of pistons.

-James

Javelin wrote:

JamesMcD wrote: I'm going to start an argument, but... It's 2.6 liters

No. Just because the rotary is smarter and is essentially a 1-stroke does not mean you get to arbitrarily assume it has double the displacement available for ONE power revolution, which is how displacement is measured.

Read my post below yours.

Javelin wrote:

JamesMcD wrote: I'm going to start an argument, but... It's 2.6 liters

No. Just because the rotary is smarter and is essentially a 1-stroke does not mean you get to arbitrarily assume it has double the displacement available for ONE power revolution, which is how displacement is measured.

The reason it's not valid to call a 13b a 1.3 liter, is that calling it so does not convey to the layperson the fact that the rotary is burning its 1.3 liters of mixture twice as often as the piston engine would, and thus the comparison is not meaningful. Speaking about it that way just makes the fanboys and ignorant people go "OMFG teh rotary rulez!" It's not a helpful way to speak about it. It's as if you were watching 4-stroke motocross and a guy showed up with a 2-stroke of the same displacement, and nobody was allowed to mention to the fans at home exactly why he kept beating everyone.

Let's make it fair. From now on I'm only going to count the displacement used by piston engines during their bang/blow strokes. An S2000 is a 1.0 liter and makes 240hp/liter. It is so awesome!

JamesMcD wrote:

Javelin wrote:

JamesMcD wrote: I'm going to start an argument, but... It's 2.6 liters

No. Just because the rotary is smarter and is essentially a 1-stroke does not mean you get to arbitrarily assume it has double the displacement available for ONE power revolution, which is how displacement is measured.

Read my post below yours.

No, still wrong. If you ASSUME it's by power stroke, it would be 6x a piston engine for "apples to apples". A piston 4-stroke engine has to have 2 crankshaft revolutions to achieve 1 power stroke. A rotary engine will achieve 3 power strokes in 1 revolution whether it wants to or not (obviously you can't make a 1/3 revolution work). So in order for a rotary to equal out, you have to times by 3 (3 power strokes per revolution) and then by 2 (2 revolutions) to equal the same number of crank revolutions as a boinger.

But that's not apples-to-apples, that's horse-hockey. Engine displacement (and therefore how much power can potentially be made) is measured as the swept volume of ONE power cycle (ie - what it takes to make "bang" happen once, x the number of rotors/chambers/cylinders/whatevers).

So, again, a 13B is 1.3 Liters.

Very nice experiment and explanation.

MrJoshua wrote:

Javelin wrote:

kreb wrote: What sort of power figure is that rotary making? It's hard to imagine that sort of ET from a wankel.

Actually, it's quite easy. There really isn't anything in a rotary to break, so they jack the boost to ludicrous-speed level (like 50psi +) and slap it in a 1500Lb or less drag car. VERY popular in Puerto Rico and Florida.

They are far less boost tolerant than you may suspect. The actual housings flex, the apex seals break, etc... It is impressive how fast some of these guys go.

Well yeah, obviously not "easy", that was poor choice of words. I should have said that it was do-able on a relatively painless scale compared to making a piston engine do the same. There's a TON of engineering into those combos.

JamesMcD wrote:

Javelin wrote:

JamesMcD wrote: I'm going to start an argument, but... It's 2.6 liters

No. Just because the rotary is smarter and is essentially a 1-stroke does not mean you get to arbitrarily assume it has double the displacement available for ONE power revolution, which is how displacement is measured.

Read my post below yours.

And replied. Your math is wrong, as is your definition of displacement as referred to in a reciprocating engine good sir.

Javelin wrote:

JamesMcD wrote:

Javelin wrote:

JamesMcD wrote: I'm going to start an argument, but... It's 2.6 liters

No. Just because the rotary is smarter and is essentially a 1-stroke does not mean you get to arbitrarily assume it has double the displacement available for ONE power revolution, which is how displacement is measured.

Read my post below yours.

No, still wrong. If you ASSUME it's by power stroke, it would be 6x a piston engine for "apples to apples". A piston 4-stroke engine has to have 2 crankshaft revolutions to achieve 1 power stroke. A rotary engine will achieve 3 power strokes in 1 revolution whether it wants to or not (obviously you can't make a 1/3 revolution work). So in order for a rotary to equal out, you have to times by 3 (3 power strokes per revolution) and then by 2 (2 revolutions) to equal the same number of crank revolutions as a boinger. But that's not apples-to-apples, that's horse-hockey. Engine displacement (and therefore how much power can potentially be made) is measured as the swept volume of ONE power cycle (ie - what it takes to make "bang" happen once, x the number of rotors/chambers/cylinders/whatevers). So, again, a 13B is 1.3 Liters.

I'm afraid you don't fully understand how rotary engines work.

Believe it or not, the rotor only turns 120 degrees per full rotation of the output shaft. Therefore, for a single rotor engine, there is one (not three) combustion event per full rotation of the output shaft.

See this video for clarification:

http://www.youtube.com/watch?v=OuId4nuxXaM&playnext=1&list=PLC38102F40B7F36AC

Is it a starlet or a Mazda 323? They have some crazy mazdas in PR, IIRC there was a 10 second FS-DE powered protege5.

It is not possible to compare a piston engine and a rotary directly, there are no apples to apples when one object is an orange.

Simply put, you can argue that it is a 3.9liter, 6 cylinder, 12 stroke, but it still is a smaller engine putting out impressive and V8 matching horsepower.

I love those little cars. Back before I was the upstanding pillar of the community I am today we spent many a night in Hunts Point, the Bronx watching those things go. It was a fun time, families picnicing in parking lots, Tiny buzzing cars carrying the front wheels through industrial parks. One of the many things Lord Guliani killed during his tenure. I'm not in any way condoning street racing but if any of you saw they old HBO show Hookers on the Point, you will realize what a great leap forward this was for an area,and once the racing left the woman came back.

In reply to JamesMcD:

I know full well how rotary engines work, there's a 12A housing & rotor sitting next to me on my desk. The revolution of the output shaft means nothing, as the combustion event does not act directly onto it. The rotor speed is what matters for power and displacement, as the rotor is what the fuel/air/fire is acting upon. The 3-to-1 action of the rotor to output is no different than a step down gear in a torque-tube engine or aircraft engine.

So again, for the output of the actual combustion chamber, a rotary would have to be either 6 times a piston engine (which is false), or 1.3L (for a 13B).

Javelin wrote: In reply to JamesMcD: I know full well how rotary engines work, there's a 12A housing & rotor sitting next to me on my desk. The revolution of the output shaft means nothing, as the combustion event does not act directly onto it. The rotor speed is what matters for power and displacement, as the rotor is what the fuel/air/fire is acting upon. The 3-to-1 action of the rotor to output is no different than a step down gear in a torque-tube engine or aircraft engine. So again, for the output of the actual combustion chamber, a rotary would have to be either 6 times a piston engine (which is false), or 1.3L (for a 13B).

Careful readers will fall upon your or my side as they may...

MrJoshua wrote: Yep! Those guys are nuts! The tiny little wheelbase means they are squirrely the entire way down the strip and through the traps. 193mph sideways!

I remember watching a really nice rotary-powered Starlet cross over the opposite lane and slam into the wall about 200' down the strip at New England Dragway 7 or 8 years ago. I think it had made a 9 second pass earlier that day.

It's witchcraft!

aussiesmg wrote: It is not possible to compare a piston engine and a rotary directly, there are no apples to apples when one object is an orange. Simply put, you can argue that it is a 3.9liter, 6 cylinder, 12 stroke, but it still is a smaller engine putting out impressive and V8 matching horsepower.

You, sir, get it,

I've always been amused by these rotary vs. piston pissing contests. Keep it up, please. Ima get a beer.

And oh yeah: Rotaries rule!

I have a wrist pin / piston slap noise coming from my rotary... and I think the Apex seals are failing in my VW... Woe is me!

Have you checked your plug gap?

I don't buy the "fewer rotations = larger displacement" argument.

A 125 cc 2 stroke engine fires on every rotation, yet is still called 125 cc's.

Displacement is a reference to the measured volume of the combustion chamber(s), not the number of strokes, cycles, or rotations.

An engine design that permits more combustion events per rotation is more efficient, but it does not alter it's displacement.

It is more accurate to say that a 4 stroke engine is producing no power at all for 75% of it's cycle time.

Shall we also have multipliers for CVCC or HCCI engines to compare to standard 4 strokes because they are more efficient? How about a wave engine? Maybe we shouldn't refer to a Prius engine as a 1.5L, since it's power output is augmented by a second electric motor?

If displacement = something other than measured volume the whole thing starts to look a little pathetic.

BTW- that little car is a frightening little ride.

SVreX wrote: I don't buy the "fewer rotations = larger displacement" argument. A 125 cc 2 stroke engine fires on every rotation, yet is still called 125 cc's. Displacement is a reference to the measured volume of the combustion chamber(s), not the number of strokes, cycles, or rotations. An engine design that permits more combustion events per rotation is more efficient, but it does not alter it's displacement. It is more accurate to say that a 4 stroke engine is producing no power at all for 75% of it's cycle time. Shall we also have multipliers for CVCC or HCCI engines to compare to standard 4 strokes because they are more efficient? How about a wave engine? Maybe we shouldn't refer to a Prius engine as a 1.5L, since it's power output is augmented by a second electric motor? If displacement = something other than measured volume the whole thing starts to look a little pathetic. BTW- that little car is a frightening little ride.

While I don't want to poke my head into this debate, the 2 stroke is a different cycle than the 4 stroke. the rotary is a 4 cycle, just like CVCC and HCCI engines are. So how you want to debate it should not factor in a 2 cycle.

As for the car, I wouldn't drive it.

Anyway, the better way to look at it is that a 2.6 liter 4-stroke piston engine is like a 1.3L rotary engine, instead of the other way around. A piston engine total displacement is the sum of all the cylider displacments, but exactly HALF of those do any work on any given revolution. A rotary engine displacement is the individual "cylinder" displacment times 2 (two rotors). Each chamber has a 654cc displacment and there are three chambers per rotor, but it takes three rotations of the eccentric shaft for all three chambers to complete a full cycle...which means that there is one complete cycle per revolution for each rotor. In other words, all the displacement is used on every rotation, whereas a piston engine only works half as much for the rated displacment. Instead of worrying about rated displacement, the correct means to compare them is "capacity". Capacity is the rating of the engines ability to pump air through them. For piston engines, Capacity = Total Displacment/2. For a rotary Capacity = Total Displacment.

Pardon my ignorance here. I've only seen them apart, but haven't held the pieces in my hands.

Seems like you have three combustion surfaces in each housing. I see them like three pistons/cylinders. If each of these is 650cc's (as demonstrated above), multiply 650 by 3 by 2 housings. 3.9l? It doesn't matter though.

Regardless, rotaries give you the horsepower of a good v6, weight of a 4 cylinder, torque of a four, and fuel efficiency of a good v8.

And that car is effing fast regardless of what it has under the hood. He must have thanked god when that 'chute blew.

In reply to SVreX:

Amen!