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Discussion Starter #1
In superbike racing, they race 750cc 4 cylinder againts 1000cc V-twins. Also 600cc 4 cylinders againts 750cc V-twins.

Why do they consider this a fair race?
 

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I ride inline 4 right now, but I have every intention of buying an RC-51.:D It only makes sence that the I-4 has a power advantage over the V-2. 4 cylinders vs. 2 will always be more powerfull at the top end. Reason being that they can support much higher RPM's do to the smaller piston size. However the V-2 has the tourque advantage due to the larger displacement. I think the V-2 will offer a better balance in the turns, but I'm only going by what I've been told. I know for sure though that the V-2 has it all over the I-4 in the tourque section.:cool: .
 

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V-Twins, to have good combustion, have to have longer strokes than 4 cylinders for the same displacement and so rev slower. If a given motor cannot rev as high as another of the same torque it makes less hp proportional to the the decrease in rpm. 1000cc V-twins however make approximatley 33% more torque than 750cc 4's by the increase in displacment. Nowadays V-twins have been getting shorter and shorter strokes. The current Duke has a 58mm stroke which I do believe is the same as a GSXR1000, and have been getting 13000rpm plus. Ten years ago this was not concievable and hence the rules for the class. Twins now are hp and torque superior. Look at Nicky's Honda doing 190's on the straights of Daytona.
But in 2004 WSB is going to 1000cc for any cylinder number, and multis will probably dominate :D
 

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Based on theory the 1000cc twin, all else equal, should be able to put out almost as much horsepower as the 750cc four cylinder bike. The FIM rules differ in comparison to current AMA rules because FIM allows twins to be a slight bit lighter to account for the lower horsepower. I think the current FIM rules are a bit behind the times though with regards to the Superbikes. Twins have enough other advantages such as narrower giving better aerodynamics. And more torque as mentioned. :)
 

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Discussion Starter #6 (Edited)
Here is why the 1000cc v-twin is in the same class as a 750cc inline 4.

v-twin: 1000cc x 10,500 RPM = 10,500,000
inline 4: 750cc x 14000 RPM = 10,500,000

Each engine uses the same amount of air and fuel.

Andy
 

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This problem was put to a British University 5 years ago, in order to find a formula that would allow the 4s to compete with the twins fairly.
Titomike it was not the Flamini that decided the rules originally :)
The rules existed from the beginning, it was a small window left by the rules to invite other manufacturrs. There was no Ducati to compete then really! The RC30 ruled WSB back then.
But Ducati saw this and as they were able to put their act together, they built the 888 superbike and got their first championship! Raymond Roche was the Ducati rider that used the potential first. Until 5 years ago the twins also had a 15 kg weight advantage over the 4s! Things had to change as the Ducati (no other twin existed) was getting better and better.
After that the balance started changing and the twins got to level weight with the 4s, they had to use lead inserts many times during rules changing.
Remember that Ducati only used the full capacity allowed (1000 cc) in the last two years, they could still win with less cc before that!
Even Honda had to revert to a V twin to win again. The RC45 only got one championship and that was with Kocinski, after a lot of money was spent.
The main problem now is that although the 4s have about the same power with the twins, and sometimes even better top speeds, they lack a lot in acceleration out of the corners as they have a much better midrange power than the 4s.
This translates in easy overtaking at the end of the straight that folow any curve ;)


Aris
 

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the reason for the displacement difference is the amount of air each type of motor can take in at certain rpm which in turn is the amount of fuel a motor can burn and horsepower it can produce. twins cant rev as high but pull in as much fuel/air mix as the high reving 4s.
 

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Twins can rev a lot higher then they used to. Both Ducati and Honda are getting 13,000+. Fours havn't gotten any higher than 15000 and I don't think the Kaw even gets that high. .75liters *15000 is only 12000 units of air a minute while the twin takes in 13000 units of air a minute. The difference of these numbers is pretty accurate to the advantage of a twin, of course power delivery is another serious advantage already mentioned.
 

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You are all wrong.

The 4s have the advantage because they have more surface area of intake and exhaust. The surface area of 16 valves is greater than the surface area of 8 slightly larger valves in the twins. Thus 4s can THEORETICALLY make more horsepower.

Of course this the theory, but when the twins started to turn more revs the disadvantage became smaller. Then there is head design and valves angles to improve flow. However, the theoretcal flow of air through more surface area is the advantage, not rpm.

This asbestos suit is gong to itch;)
 

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A lot of talk about twins being superior, but just to put it back in perspective, that is comparing 750cc inline4 with 1000cc twin, not equal displacement. I'm SO sorry, but put an R1 or GSX-R1000 out there in World Superbike and ... what happened to the twins? That's because a GSX-R1000, for example, feels no torque disadvantage to a Ducati 998, while having a nice helpin' more of ponies on tap.

An interesting bike would be something like a GSX-R1000 that was retuned, taking away 20 ponies or so until it's down to 120hp, and shoving all that into more torque and more midrange. An inline-4 can be made to act like a V-twin if you wanted it to... they just don't, because it can put out so many ponies while still being respectable in the torque department.
 

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If your curious how 1000cc 4-in-lines will compare with 1000cc V-twins in Superbike racing, watch the British Superbike Series. BSB changed the rules this year and they'll be competing against each other. April 1st at Donnington Park is the first race.
 

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dryheat said:
If your curious how 1000cc 4-in-lines will compare with 1000cc V-twins in Superbike racing, watch the British Superbike Series. BSB changed the rules this year and they'll be competing against each other. April 1st at Donnington Park is the first race.
So what? Canadian superbike allows 1000cc 4's to run with twins. Crevier (RC51) and Taylor(RC51) placing 1st and 6th overall respectively.
 

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VFRSQUID said:


So what? Canadian superbike allows 1000cc 4's to run with twins. Crevier (RC51) and Taylor(RC51) placing 1st and 6th overall respectively.
Fine. You don't have to wait for BSB. The point has been made:V-twins can run with 4-in-lines with the same displacement.

That's what.
 

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You guys are comparing apples to oranges when talking factory superbikes and bikes such as GSXR 1000s. Factory RC-51s are putting out a significant amount of torque and horspower over what a Gix 1000 does. It is two completely different animals. AMA Formula Xtreme bikes are pumped up Gix1000s, R1s and Honda 929/954s with upgraded suspension and still don't quite run the lap times of a GSXR750 or Honda1000cc Superbike. Superbikes are currently in a class by themselves. The FXtreme bikes are getting closer but they aren't there. The factory RCs put out around 180rwhp while a Suzuki GSXR1000 puts out around 150rwhp. The Suzuki FXtreme bike are probably putting out about 185rwhp and still can't beat a factory superbike because the chassis just isn't able to handle it like the superbikes.

750cc 4 cylinder bikes are comparible to 1000cc twins. Comparing 1000cc four cylinder street bikes to 1000cc twin cylinder street bikes is a joke. :rolleyes:
 

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desmo079 said:
The 4s have the advantage because they have more surface area of intake and exhaust. The surface area of 16 valves is greater than the surface area of 8 slightly larger valves in the twins. Thus 4s can THEORETICALLY make more horsepower.
Other factors equal, a 750cc four has slightly greater valve area than a 1000cc twin. Let's compare the Ducati 998 and Suzuki GSX-R750. The two share a nearly identical bore/stroke ratio of 1.57, so that "other factor" is indeed equal. (Duc's dimensions are 100x63.5, Suzuki's 72x46).

The Suzuki's cylinder cross-section area, which limits valve area, is 4071.5mm^2, with a total for its four cylinders of 16286mm^2. The Duc's cylinder cross section area is 7854mm^2, with a total of 15708mm^2. Thus the four has a 3.7% edge in cross-section area.

However, that advantage works only if the four is capable of revving high enough to exploit its valve area. And revs are where the twins seem to get the better of the fours. With its short 46mm stroke, the Suzuki should be able to rev 38% higher than the Duc. If it could, it would have more than enough extra revs to compensate for its displacement deficit.

But the extra revs don't seem to be there. Fasthrc noted that the twins revs to 13,000 and the Zook to 15,000, giving the four less than half its theoretical 38% rev margin.

Kevin Cameron wrote a column a few years ago about the quest for revs in Superbike. At that time, engine builders had reached a point of diminishing returns, where the added friction at higher revs consumed the added power produced--the marginal return from higher revs had gone negative.

I'll go out on a limb here (and, hopefully, provoke a response from someone more knowledgable than myself) and suggest that the fours may be suffering from insufficient bearing surface area. To keep the engine narrow, rod and main bearings are compromised. OTOH, a V-twin, a narrower package to begin with, can accommodate more generous bearing dimensions.
 

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DataDan said:


Other factors equal, a 750cc four has slightly greater valve area than a 1000cc twin. Let's compare the Ducati 998 and Suzuki GSX-R750. The two share a nearly identical bore/stroke ratio of 1.57, so that "other factor" is indeed equal. (Duc's dimensions are 100x63.5, Suzuki's 72x46).

The Suzuki's cylinder cross-section area, which limits valve area, is 4071.5mm^2, with a total for its four cylinders of 16286mm^2. The Duc's cylinder cross section area is 7854mm^2, with a total of 15708mm^2. Thus the four has a 3.7% edge in cross-section area.

However, that advantage works only if the four is capable of revving high enough to exploit its valve area. And revs are where the twins seem to get the better of the fours. With its short 46mm stroke, the Suzuki should be able to rev 38% higher than the Duc. If it could, it would have more than enough extra revs to compensate for its displacement deficit.

But the extra revs don't seem to be there. Fasthrc noted that the twins revs to 13,000 and the Zook to 15,000, giving the four less than half its theoretical 38% rev margin.

Kevin Cameron wrote a column a few years ago about the quest for revs in Superbike. At that time, engine builders had reached a point of diminishing returns, where the added friction at higher revs consumed the added power produced--the marginal return from higher revs had gone negative.

I'll go out on a limb here (and, hopefully, provoke a response from someone more knowledgable than myself) and suggest that the fours may be suffering from insufficient bearing surface area. To keep the engine narrow, rod and main bearings are compromised. OTOH, a V-twin, a narrower package to begin with, can accommodate more generous bearing dimensions.
Very well though out post. 'Course totally irrelevant once fours get to use 1000cc also.:)

You sure do live up to your name, DataDan.
 
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