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  #31  
Old 05-25-2009, 06:17 PM
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Quote:
Originally Posted by clutch-monkey View Post
does it actually work?
I am pretty sure it is just the outer casings bolted together. No eccentric shaft no rotors.

Can you imagine the forces an eccentric shaft that long would have to cope with?!
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  #32  
Old 05-25-2009, 06:43 PM
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no, that's why i asked
i remembered there being a limiting factor to these kind of enlarged rotary's, but couldn't remember what it was
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  #33  
Old 05-25-2009, 06:54 PM
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well the real limiting factor is this:

it is only possible to get the eccentric shaft into the engine if it has 2 or less lobes. the three rotor 20B actually has a two-piece eccentric shaft which is aligned with a key. The first 4 rotor engine had a 3 piece eccentric shaft (1 shaft with two lobes in the middle and 1 lobe added to each end) and later versions where made with 2 piece shafts (keyed joint in the middle).

The more keyed joints you have the weaker the eccentric shaft.

You could possibly make a 6 rotor wankel engine but anything over that is going to be difficult (not to mention ridiculously long and unweildy).
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  #34  
Old 05-25-2009, 09:35 PM
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Quote:
Originally Posted by hightower99 View Post
There really isn't anything to argue about it is simple, all three sides of each rotor are contributing to engine displacement at all times. Saying the R26B is only 2.6L engine is like calling a 2L inline 4 a 500cc engine... it just doesn't make sense at all. Do you really think that the R26B only sucked 2.6L air in when all the rotors did 1 full revolution?

Mazdas marketing team came up with the idea that engine displacement should be defined by the amount displaced by one side of each rotor in the engine...

Think about it Matra you have an RX-8, you know the kind of mileage it gets. Does it make sense that a 1.3L engine needs that much fuel? or does it make more sense that a 3.9L engine needs that much fuel?
That only accounts for the difference between shaft and rotor speed. The rotor spins 3x slower than the shaft, so theres still only one power pulse per rotation.

Its more comparable to a 2 stroke engine, which has a similar 1 pulse per rotation and has a x2 equivalency factor for displacement.
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  #35  
Old 05-25-2009, 10:25 PM
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Quote:
Originally Posted by hightower99 View Post
well the real limiting factor is this:

it is only possible to get the eccentric shaft into the engine if it has 2 or less lobes. the three rotor 20B actually has a two-piece eccentric shaft which is aligned with a key. The first 4 rotor engine had a 3 piece eccentric shaft (1 shaft with two lobes in the middle and 1 lobe added to each end) and later versions where made with 2 piece shafts (keyed joint in the middle).

The more keyed joints you have the weaker the eccentric shaft.

You could possibly make a 6 rotor wankel engine but anything over that is going to be difficult (not to mention ridiculously long and unweildy).
ok, cool.
Quote:
Originally Posted by hightower99 View Post
Think about it Matra you have an RX-8, you know the kind of mileage it gets. Does it make sense that a 1.3L engine needs that much fuel? or does it make more sense that a 3.9L engine needs that much fuel?
i thought the fuel economy thing was mainly because rotary's haven't been developed/researched as much as piston engines
like, a small block chev back in the day would use more fuel/be less efficient than a contemporary LS series engine, that kind of thing
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  #36  
Old 05-25-2009, 11:10 PM
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Quote:
Originally Posted by hightower99 View Post
I guess you fell for mazdas whole marketing spiel...

There really isn't anything to argue about it is simple, all three sides of each rotor are contributing to engine displacement at all times. Saying the R26B is only 2.6L engine is like calling a 2L inline 4 a 500cc engine... it just doesn't make sense at all. Do you really think that the R26B only sucked 2.6L air in when all the rotors did 1 full revolution?
No it isen't..
If we take the 13B engine it only uses 654ccm (As is present in one such rotary department) to fulfill one combustion cycle. (Mind you, this cycle has been all the way round the engine). Just because another cycle starte before the other is complete dosen't mean it uses the collected size to power it. Even if that was the case, then you wouldn't have to count the size as 3 times as big since it effectivly only has 1,5 combustion cycles started at any one time. (Hence the reason why it's displacement is multiplied by 1,5 should you choose to run this engine in a race)

Quote:
Originally Posted by hightower99 View Post
IDo you really think that the R26B only sucked 2.6L air in when all the rotors did 1 full revolution?
You do realize that 4stroke engines uses 2 crakshaft revolutions per combustion cycle? Should we then double their effective displacement? Compared to the rotary which only uses one? Fact is, piston movements/rotary rotations just dosen't have anything to do with the effective displacement.



Quote:
Originally Posted by hightower99 View Post

Think about it Matra you have an RX-8, you know the kind of mileage it gets. Does it make sense that a 1.3L engine needs that much fuel? or does it make more sense that a 3.9L engine needs that much fuel?
Try squeezing 180hp from a 1,3 piston engine and see how much mileage you get. I bet you it won't be much more than 10km/l which is roughly what the Rx8 does. Hell, my 1,9 engine (With 110hp) is allmost down there. Besides that. You never see 1,3 piston engines in so large cars, which also gives to give a wrong impression of mileage.

Thing is. You just can't compare piston and wankel engines. (Even tho i just did)
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  #37  
Old 05-26-2009, 12:29 AM
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CAMS here in Australia have a multiplication factor they run for rotarys is capacity cc X 1.8 or supercharged rotary cc x 3.06
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  #38  
Old 05-26-2009, 04:47 AM
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thanks fpv and bueno for assisting ht's understanding.
The whole issue of why rotaries got to win everything they tried the first time out is that the regs didn't cover the complexity of swept volue of a wankel chamber.
So the regs were then changed and played aroudn with till various equivalency figures were agreed.

So ht, initilaly the argument for 3*volume was proposed but clearly over penalised the performance of the engine. As charged says folks then approached common grounds ( with a few small variations ) across motoring organsiations.

Therea re still odd cases ... eg in Ireland MY car is taxed as a 1.3 but here int he UK ( and everywhere else I know of ) it's seenas a 2.6 !
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  #39  
Old 05-26-2009, 08:35 AM
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Quote:
Originally Posted by fpv_gtho View Post
That only accounts for the difference between shaft and rotor speed. The rotor spins 3x slower than the shaft, so theres still only one power pulse per rotation.

Its more comparable to a 2 stroke engine, which has a similar 1 pulse per rotation and has a x2 equivalency factor for displacement.
hmmm so if I put a 3:1 gearset between a normal piston engine and the output shaft then it's displacement should also be divided by 3?

I am not talking about equivalency factors that are used for racing I am just talking about the actual displacement caused by the moving parts in the engine.

Also 2 strokes don't have x2 equivalency factor when you buy one for street use. If you buy a 250cc 2-stroke single cylinder motorcycle then the engine will have a bore around 68mm and a stroke around 68mm (if its a square engine) it won't be a 125cc engine...

Quote:
Originally Posted by clutch-monkey
i thought the fuel economy thing was mainly because rotary's haven't been developed/researched as much as piston engines
like, a small block chev back in the day would use more fuel/be less efficient than a contemporary LS series engine, that kind of thing
Actually Wankel engines are almost as developed as any modern piston engine is. The new 16X engine that is coming out has direct petrol injection and runs at a decent compression ratio. The main reason why wankel engines are inefficient is more to do with current designs having too much surface area per volume especially during combustion, this leads to high heat loss.


Quote:
Originally Posted by Buen
If we take the 13B engine it only uses 654ccm (As is present in one such rotary department) to fulfill one combustion cycle. (Mind you, this cycle has been all the way round the engine). Just because another cycle starte before the other is complete dosen't mean it uses the collected size to power it. Even if that was the case, then you wouldn't have to count the size as 3 times as big since it effectivly only has 1,5 combustion cycles started at any one time. (Hence the reason why it's displacement is multiplied by 1,5 should you choose to run this engine in a race)
What? by that reasoning then a 2L inline 4 piston engine should be called a 500cc engine as only one combustion event is occuring at any one time!?!

All three (3) sides of each rotor in a wankel engine is producing displacement at all times and one (1) full revolution (thats 360 degrees) of the rotor will displace a total of 1962cc.

Quote:
Originally Posted by Buen
You do realize that 4stroke engines uses 2 crakshaft revolutions per combustion cycle? Should we then double their effective displacement? Compared to the rotary which only uses one? Fact is, piston movements/rotary rotations just dosen't have anything to do with the effective displacement.
Its not about how many revolutions of the crank is needed to complete a full cycle! I am not talking aout "effective" displacement I am talking about actual engine displacement... Each wankel rotor uses three sides to produce displacement... a piston only uses one side in a normal engine.


Matra: I fully understand that there are different equivalency factors that are applied when a certain amount of equalisation is needed in racing enviroments. I also fully understand that Mazda was able to get the engines classified as 1.3L engines for tax purposes and that some countries have since reclassified them as 2.6L engines...

But none of that has anything to do with actual displacement of the engines which is what I am talking about.
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  #40  
Old 05-26-2009, 11:09 AM
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I can't believe this hasn't been said yet, but 7.0L V8 as in the LS7.R. Great sound, outstanding performance and damn near bulletproof.
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  #41  
Old 05-26-2009, 11:38 AM
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ht, the ACTUAL displacement of the engine by traditional means is 1.3
THe "combustion chamber maximum size".
Having to talk about swept voume and it's relevance makes it confusing for some.

NO, it's not the same as a "gear" for the Wankel. THe offset crank is as much a part as a classic banger. So again, another point of contention on what shoudl and shoudl not be taken into account.

The actual "displacement" is the SMALLEST of the figures ht.
When it goes "bang" that is the power pulse and thus SHOULD be the only one of interest. ... or to borrow one of your analogies, shuold a single cylinder engine be compared the same as a rotary IF it spins 3 times faster ?

By ALL measnures the only one that is widely accepted as NOT the right one is to add up ALL the chambers of a rotary !!!
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  #42  
Old 05-26-2009, 11:45 AM
fpv_gtho fpv_gtho is offline
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Quote:
Originally Posted by Matra et Alpine View Post
thanks fpv and bueno for assisting ht's understanding.
Clearly we havent.

HT, forget about the displacement, swept volume and all that crap and just concentrate on the power pulses. Just like a 2 stroke, a wankel rotary produces a pulse for each RPM. 4 strokes produce a pulse for every 2 RPM. That is why x2 is the most common equivalency for both. Your scenario has the factor applied the wrong way; a 250cc 2 stroke is equivalent to a 500cc 4 stroke.

RPM isnt measured by the rotation of the rotor in the wankel, its by the rotation of the eccentric shaft, which is 3x that of the rotor. That means when the engine reads 9000rpm, the rotor is only spinning at 3000rpm. That balances having 3x the combustion surfaces, as at 9000rpm you've still only got 9000 pulses per minute, whilst a 9000rpm 4 stroke reciprocating motor only has 4500.
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  #43  
Old 05-26-2009, 12:38 PM
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Btw, when talking about 2stroke engines i think Fpv ment with a 2xequivilancy factor that a 2 stroke engine produces 2 times the horse power with the same displacement.

Edit: On a little side note. When i was much younger and meddeling with scooters. I once at a gathering saw 1 person with a 80ccm tuning kit trow a massive 26hk. Allthough theese machines won't last much more than 250-500km before needing to get the piston replaced.

Last edited by Buen; 05-26-2009 at 12:40 PM.
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  #44  
Old 05-26-2009, 03:14 PM
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haha there's actually a company that makes small rotaries to suit go karts, would be awesome imo (i'd choose it for a race engine...gokart racing.)
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  #45  
Old 05-26-2009, 08:54 PM
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Quote:
Originally Posted by Buen View Post
Btw, when talking about 2stroke engines i think Fpv ment with a 2xequivilancy factor that a 2 stroke engine produces 2 times the horse power with the same displacement.
hence DKW sold its cars as the 3=6 models....(as if they were 6 cylinder engines).
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