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Discussion Starter #1
Read the following link....http://www.motorcycledaily.com/09november06_torque.htm

Its hard not to believe that this next year (2007) will be the best chance for 4 cylinder bikes to beat Ducati in WSBK, because if the rules allow 1200cc twins for 2008, it appears that Ducati should easily dominate once again with the "Torque Advantage". This will also force the japanese manufacturers to reconsider building twins (i.e. RC51) for racing again. Is this inevitable?

What are your thoughts?
 

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jsdp said:
Read the following link....http://www.motorcycledaily.com/09november06_torque.htm

Its hard not to believe that this next year (2007) will be the best chance for 4 cylinder bikes to beat Ducati in WSBK, because if the rules allow 1200cc twins for 2008, it appears that Ducati should easily dominate once again with the "Torque Advantage". This will also force the japanese manufacturers to reconsider building twins (i.e. RC51) for racing again. Is this inevitable?

What are your thoughts?
I'm not always super-impressed with the opinions on that site.

Yes, torque makes a difference. But there's more to it than that.

What we're really talking about is the ability of the engine to put power to the ground effectively, not necessarily torque.

It's the power characteristics of the V-Twin which allow it to hook up so well.

If you watched AMA superbike at all this year, and Fontana in particular, you would see that the Ducatis were getting whipped coming off corners by the Suzukis. This was the "old" strength of the twin. Why is this? Probably many possibilities:

1. Lots of rumors Suzuki was cheating at the time with traction control.
2. Ducati is likely wringing every last HP out of the bikes and may be sacrificing torque (efficient cylinder filling at lower rpm) to do it.

Once traction control was introduced, the Ducatis made up a large amount of ground on the twins in AMA. This is not due to superior torque.

Saying that it's about a "torque advantage" is simplistic, in my view. There's much more to it than that.
 

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The rules makers can always tweak things to gain parity if one manufacturer has an apparent advantage. This has been demonstrated over and over again through minimum weight differences for different engine layouts or restrictions on intake diameter etc.

Like acruhl says, traction control eliminates much of the advantage twins have coming off of corners. When running at the maximum, the twins uneven firing impulse with up to 450 degrees of crankshaft rotation between firing allows the tire to grip while a 4 cylinder engine firing every 180 degrees can spin the tire up unintentionally when pushed hard. Traction control cancels this.
 

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Discussion Starter #4
acruhl said:
I'm not always super-impressed with the opinions on that site.

Yes, torque makes a difference. But there's more to it than that.

What we're really talking about is the ability of the engine to put power to the ground effectively, not necessarily torque.

It's the power characteristics of the V-Twin which allow it to hook up so well.
Good point, and assuming that this is true the Ducati should get a better drive without the displacement advantage (which yields more torque).

acruhl said:
If you watched AMA superbike at all this year, and Fontana in particular, you would see that the Ducatis were getting whipped coming off corners by the Suzukis. This was the "old" strength of the twin. Why is this? Probably many possibilities:

1. Lots of rumors Suzuki was cheating at the time with traction control.
2. Ducati is likely wringing every last HP out of the bikes and may be sacrificing torque (efficient cylinder filling at lower rpm) to do it.

Once traction control was introduced, the Ducatis made up a large amount of ground on the twins in AMA. This is not due to superior torque.
I agree with your assessment, but I don't believe the Ducati has superior torque with 1000cc. They will however have it with 1200cc and combined with the power characteristics of the V-Twin, I believe it will be a distinct advantage.

acruhl said:
Saying that it's about a "torque advantage" is simplistic, in my view. There's much more to it than that.
There are many variables, but I am assuming that the writer was just trying to make a point assuming all other things are equal.
 

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Discussion Starter #5 (Edited)
Koop said:
Like acruhl says, traction control eliminates much of the advantage twins have coming off of corners. When running at the maximum, the twins uneven firing impulse with up to 450 degrees of crankshaft rotation between firing allows the tire to grip while a 4 cylinder engine firing every 180 degrees can spin the tire up unintentionally when pushed hard. Traction control cancels this.
You are absolutely right about traction control. It did/does eliminate the advantage of twins, but assuming that twins have 20% more torque and equal horsepower to the 1000cc 4's in 2008 along with traction control, it appears a bit unfair if all other things are equal.
 

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jsdp said:
You are absolutely right about traction control. Its did/does eliminate the advantage of twins, but assuming that twins have 20% more torque and equal horsepower to the 1000cc 4's in 2008 along with traction control, it appears a bit unfair if all other things are equal.
It's not a foregone conclusion that a twin WILL absolutely have more torque than a 4 cylinder engine. It's just usually the case when one is tuned sanely :)

And in the sane world, torque is cylinder filling, and twins do this well because of the longer stroke.

Now, since we're talking about variables, let's talk about firing order.

What would happen if the 4 cylinder bikes were allowed to change their firing order, or even crank layout? Still think the twins would have an advantage? It's not so clear I think.

Is it really torque that is the advantage, or HP? After all, it's HP that is the measure of work done.

Traction control helps a lot, but still, if you change the firing order so that you get optimum "hook up" with the back tire, you can allow more power to the ground, which means "less" traction control and more power.

I'm not trying to make a statement or answer a question, I'm merely pointing out that the word "torque" is too difficult to single out to make a claim that it's the reason for anything.
 

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From what I understand, Ducati's argument is based on future development. They claim the 999 Testastretta is fully developed and will not produce much more in the way of usuable power. However, 4 cylinder litre bikes still have development potential.

Mean piston speed calculations don't seem to support this argument. To produce more HP you must either find an increase in Brake Mean Effective Pressure (BMEP = torque) or you must spin the engine faster. The Testastretta stroke of 58.8mm is similar to that of 4 cylinder litre bikes, so the piston speed limits should be similar. Of course the Ducati is accelerating a much larger and heavier piston with it's 100 mm bore, but that's not unusually large compared to automobile racing engines.

I'm sure there's some substance to their argument, I just don't see it (yet). Perhaps it's the bottom end, maybe the crankcase can't support any further inertial load?
 

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Once you get to the RPM limits defined by a given stroke, the bore cannot be increased beyond a certain point due to limits on the flame travel across the bore.

As RPM's climb, the time available for combustion decreases and flame can only travel a given distance in that amount of time. Hence, for a given RPM, the bore cannot be increased beyond a certain point because the fuel mixture at the boundaries of the cylinder will not be burned efficiently. In short, the higher the redline, the less time available for combustion and the smaller the bore must be.

Since the Ducati twin already utilizes what is basically the same stroke as (some of) the Japanese fours, the twin has hit its limit with respect to bore sizes and RPM limits but the fours have not.

There are some other factors at work, including the fact that the Ducati motor because it is such a high-revving twin must be so extensively modified ($$$$$$) and replaced so often (even more $$$$$$$$) that Ducati wants rules that will allow them to continue to race without having to spend so much money. In exchange for the displacement advantage, they will agree to certain other rules that decrease the displacement advantage in other ways.

And by the way, the 999R uses a 104 mm bore.
 

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Don't forget that in MotoGP Ducati has - despite decades of race experience with the twin-cylinder format - never even attempted to use that layout and instead campaigned a four-cylinder motor.
 

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So add another spark plug or 2 :)

All kinds of stuff at work here.

I think the main points are:

1. It's too expensive to make a 1000cc twin competitive with a 1000cc 4, as was stated.
2. Going solely by numbers isn't going to cut it, someone has to watch what is actually happening and then make rules changes to compensate.
3. Whoever makes the most effective overall package will win, given that someone can keep the rules at least appearing fair this time. (This time meaning in this era of twin cylinder displacement being bigger than the fours again)
 

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Discussion Starter #11 (Edited)
acruhl said:
Now, since we're talking about variables, let's talk about firing order.

What would happen if the 4 cylinder bikes were allowed to change their firing order, or even crank layout? Still think the twins would have an advantage? It's not so clear I think.
I believe they would have a "torque advantage", only due to the fact that the twins will be 1200cc vs 1000cc for the 4's which from my basic knowledge of engines means that substantial displacement increases have always yielded more absolute torque in these situations. I believe the 1098 has 90.4 lbs/ft of torque mainly because of the additional 100cc of displacement over current 1000cc 4's. Again I may not have been clear before, but I am simply stating that we are not talking about all the variables, just torque and its relationship to displacement.

acruhl said:
Is it really torque that is the advantage, or HP? After all, it's HP that is the measure of work done.
I am assuming Ducati were/will be allowed to increase their twins to 1200cc based on the fact that they have a HP disadvantage currently. And 1200cc may/will make them on equal footing with regard to HP with the 1000cc 4's.

acruhl said:
Traction control helps a lot, but still, if you change the firing order so that you get optimum "hook up" with the back tire, you can allow more power to the ground, which means "less" traction control and more power.

I'm not trying to make a statement or answer a question, I'm merely pointing out that the word "torque" is too difficult to single out to make a claim that it's the reason for anything.
The only claim that is being made is that 1200cc appears to be a distinct advantage over 1000cc with regard to torque. I believe that there isn't a simple formula for regulations to equalize twins vs 4's and that point is made by the writer.
 

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emmvee said:
Once you get to the RPM limits defined by a given stroke, the bore cannot be increased beyond a certain point due to limits on the flame travel across the bore.

As RPM's climb, the time available for combustion decreases and flame can only travel a given distance in that amount of time. Hence, for a given RPM, the bore cannot be increased beyond a certain point because the fuel mixture at the boundaries of the cylinder will not be burned efficiently. In short, the higher the redline, the less time available for combustion and the smaller the bore must be.

Since the Ducati twin already utilizes what is basically the same stroke as (some of) the Japanese fours, the twin has hit its limit with respect to bore sizes and RPM limits but the fours have not.

There are some other factors at work, including the fact that the Ducati motor because it is such a high-revving twin must be so extensively modified ($$$$$$) and replaced so often (even more $$$$$$$$) that Ducati wants rules that will allow them to continue to race without having to spend so much money. In exchange for the displacement advantage, they will agree to certain other rules that decrease the displacement advantage in other ways.

And by the way, the 999R uses a 104 mm bore.
Flame speed is indeed important, but there are ways to improve it through combustion chamber design etc. Formula 1 (car) engines currently feature a bore to stroke ratio of ~2.25:1. So with 40 - 44mm strokes they have 90 - 100mm bores and they spin 19,000 rpm. Their fuel has been regulated for several years to be somewhat close to commercially available fuel as well.

The more I think about it, the more I'm leaning towards bottom end limitations. Who wants to blow up cranks or replace crankcases after every race? Lower inertia in the fours allows better reliability at high piston speed.

Increasing displacement in the twin will allow similar power output at lower rpm - increasing reliability.
 

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Good discussion, thanks :) Other than the mentioned spark addition (stronger and more) can't they better atomize fuel to get to the periphery?



Doesn't the GSXR cup have a dyno measured tech inspection and limits to within +-__% bhp/torque?

Come up with a safe number for worldwide tracks on a power to weight ratio scale and then enforce the minimum weights and max bhp/torque.
 

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Discussion Starter #14
emmvee said:
In exchange for the displacement advantage, they will agree to certain other rules that decrease the displacement advantage in other ways.
I hope this is true.

I am concerned that small companies like MV and Aprilia that are investing in a WSBK superbike program for 2008 with 1000cc 4's may have a very tough time being competitive with Ducati's 1200cc twins. I don't want to see history repeat itself with Ducati dominating and forcing other manufactures to develop twins to be truly competitive. That would be devastating to small companies like MV and Aprilia.
 

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I started to reply but had to bail out (work). A lot of this has been covered already but I will keep it in just to make my post clear. The work (torque) an engine produces is a function of two things only, displacement and compression ratio. Regardless of the number of cylinders present, the maximum theoretical torque depends only on those two things. Power is the rate at which work is done. It is dependent on two variables also. First is torque, the other is RPM. So given two engines with identical compression and displacement, but different numbers of cylinders they will have the same theoretical peak torque.
To increase power you need to either increase torque or increase the rpm. If you can't change the displacement, the only way you can increase the theoretical torque is to increase the compression ratio (which results in increased engine efficiency). Unfortunately the upper limit of the CR is determined by auto ignition, you can only increase the compresssion a certain degree before auto-ignition (detonation) occurs which will damage the engine. The only other way to increase power is to increase the RPM. As has already been mentioned the upper limit of RPM is determined by the flame propagation speed. As RPM increase the time for combustion to occur is very short, milliseconds or less. For any given displacement, an engine with more cylinders has will have a smaller bore which means the flame doesn't need to travel as quickly to reach the cylinder wall. Yes you can increase turbulence in the cylinder which improves mixing, which in turn increases flame front speed, but there is an upper limit to the speed at which the flame can propagate. If I recall correctly its around 20,000 ft/sec, but this is totaly off the top of my head. Another issue with the twins is the cylinder surface area. The cylinder walls are always cooler than the rest of the cylinder. The larger cylinders quench the flame by taking heat away from the combustion process. This results in a less efficient burn.
What is really important as it relates to bikes is the firing order. Ducati's Desmosedicci is an attempt to combine the best of both worlds. By utilizing a four cylinder configuration they take advantage of a smaller bore which increases the upper RPM limit resulting in more power. The Twin pulse design means that two cylinders fire at the same time resulting in one power pulse every 360 degrees of crankshaft rotation, just like a twin. This gives the tire more time to recover if it begins to break traction. The only other advantage to the V4 configuration is really a packaging issue. You could design an I-4, V-4, V6, or whatever to behave in whatever manner you want, it simply matters where you have the cylinders fire. Unfortunately thee are trade-offs and most of those center around the need for a heavier crank.

So ultimately, a twin doesn't have any torque advantage over an I-4. If it gets a displacement advantage it. But with electronics controlls, that is becoming less and less of an advantage.
 

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RobP said:
The work (torque) an engine produces is a function of two things only, displacement and compression ratio. Regardless of the number of cylinders present, the maximum theoretical torque depends only on those two things. .
I think you mean to say cylinder pressure, not CR. Two engine of the same displacement and compression ratio can have a wide variation in torque output. It's a matter of filling the cylinder and developing cylinder pressure. For comparison sake, this is usually expressed as BMEP (Brake Mean Effective Pressure).
 

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JamesC said:
Good discussion, thanks :) Other than the mentioned spark addition (stronger and more) can't they better atomize fuel to get to the periphery?



Doesn't the GSXR cup have a dyno measured tech inspection and limits to within +-__% bhp/torque?

Come up with a safe number for worldwide tracks on a power to weight ratio scale and then enforce the minimum weights and max bhp/torque.

We've got *limits* today that were thought impossible a few years ago and I'm sure today's limits won't remain for long.

Probably a LOT of things they can do to overcome the *limits* on flame propagation but it's likely a function of diminishing returns combined with the cost/benefit ratio of all the attendant work. Plus, you've got the limits of the fuel that's actually legal in WSB or AMA that they're got to work around.

As far as rules are concerned, no matter what rules you come up with, twins and fours are different beasts, and not just due to power delivery characteristincs. You've got width and polar moment of inertia of motors, cg of motors in both planes, centralization of mass differences between the two types, contraints with respect to location of swingarms, riders, airboxes, transmissions, etc., relative to center of mass... Someone will protest rules that others claim are "fair for all." How often has it been said that the winner is determined at the rulesmaking session...

Traction control may minimize the differences between twins and fours but is Ducat's recent success due to a more sophisticated traction control, or is it just that the inherent characteristics of twins make them easier to manage - whether it's a rider or a computer doing the bulk of the managing - and will Ducati's current TC advantage be short-lived once the makers of the fours solve the more difficult puzzle of managing an inline four? Way beyond me! ;)
 

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Discussion Starter #18 (Edited)
RobP said:
I started to reply but had to bail out (work). A lot of this has been covered already but I will keep it in just to make my post clear. The work (torque) an engine produces is a function of two things only, displacement and compression ratio. Regardless of the number of cylinders present, the maximum theoretical torque depends only on those two things. Power is the rate at which work is done. It is dependent on two variables also. First is torque, the other is RPM. So given two engines with identical compression and displacement, but different numbers of cylinders they will have the same theoretical peak torque.
To increase power you need to either increase torque or increase the rpm. If you can't change the displacement, the only way you can increase the theoretical torque is to increase the compression ratio (which results in increased engine efficiency). Unfortunately the upper limit of the CR is determined by auto ignition, you can only increase the compresssion a certain degree before auto-ignition (detonation) occurs which will damage the engine. The only other way to increase power is to increase the RPM. As has already been mentioned the upper limit of RPM is determined by the flame propagation speed. As RPM increase the time for combustion to occur is very short, milliseconds or less. For any given displacement, an engine with more cylinders has will have a smaller bore which means the flame doesn't need to travel as quickly to reach the cylinder wall. Yes you can increase turbulence in the cylinder which improves mixing, which in turn increases flame front speed, but there is an upper limit to the speed at which the flame can propagate. If I recall correctly its around 20,000 ft/sec, but this is totaly off the top of my head. Another issue with the twins is the cylinder surface area. The cylinder walls are always cooler than the rest of the cylinder. The larger cylinders quench the flame by taking heat away from the combustion process. This results in a less efficient burn.
What is really important as it relates to bikes is the firing order. Ducati's Desmosedicci is an attempt to combine the best of both worlds. By utilizing a four cylinder configuration they take advantage of a smaller bore which increases the upper RPM limit resulting in more power. The Twin pulse design means that two cylinders fire at the same time resulting in one power pulse every 360 degrees of crankshaft rotation, just like a twin. This gives the tire more time to recover if it begins to break traction. The only other advantage to the V4 configuration is really a packaging issue. You could design an I-4, V-4, V6, or whatever to behave in whatever manner you want, it simply matters where you have the cylinders fire. Unfortunately thee are trade-offs and most of those center around the need for a heavier crank.

So ultimately, a twin doesn't have any torque advantage over an I-4. If it gets a displacement advantage it. But with electronics controlls, that is becoming less and less of an advantage.
Wow, thank you for the education. I learned alot from your post.

In summary, are you saying that if theoretically we cannot increase compression ratios/cylinder pressure, a 200cc advantage = a torque advantage for the twins?
 

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emmvee said:
Traction control may minimize the differences between twins and fours but is Ducat's recent success due to a more sophisticated traction control, or is it just that the inherent characteristics of twins make them easier to manage - whether it's a rider or a computer doing the bulk of the managing - and will Ducati's current TC advantage be short-lived once the makers of the fours solve the more difficult puzzle of managing an inline four? Way beyond me! ;)
Troy Corser was quoted last season as saying the Ducati traction control was so superior that Bayliss was on the throttle way before he (Corser) could even think about turning up the wick through the corners.
 

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RobP said:
I started to reply but had to bail out (work). A lot of this has been covered already but I will keep it in just to make my post clear. The work (torque) an engine produces is a function of two things only, displacement and compression ratio. Regardless of the number of cylinders present, the maximum theoretical torque depends only on those two things. .

I would think that for a given bore/stroke ratio, a four cylinder motor can take advantage of the greater number of valves compared to a twin of the same displacement and more importantly, take advantage of the greater valve area, thus increasing its efficiency relative to the twin. This would also change the power characteristics of such a motor due to the greater valve area to displacement ratio.
 
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