Torque, Horse Power and Acceleration (2014)

Rohan said:

comnoz said:

Here is a good illustration of torque vs horsepower. The next 1/8th mile would have been different.

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Remember that horsepower has to have torque to go with it - by definition.
So the 'horsepower' engine just doesn't have as much of the torque ... low down...

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You are absolutely right. The Honda produces it's torque at high RPM and the Harley produces it's torque at low. Unfortunately for the Honda it's torque peak comes in too late to be of any use in 1/8th mile with stock gearing. Jim

is it really ONLY max cylinder filling that dictates max rear wheel torque?

It dictates maximum crankshaft torque if the mixture and burn are right.

Rear wheel torque is very dependent on the gearing. Jim

comnoz said:

hobot said:

Most everyone seeks a flatish torque curve, but I've tasted what is like to have increasing torque curves to red line in two Nortons, couple outboards and cage V8's it allows constant 10%-ish tire spin just about all the way to top out. It gets harder and harder to break traction the faster ya go in a bee line on pavement and hill climbs. Also makes shifting optional depending on traction.

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If you have an increasing torque curve all the way to redline then your redline must be really really low. Jim

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Heavy flywheels will not increase the torque of the engine. Of course the energy that is stored in a rapidly spinning flywheel may certainly help get a good launch in a drag race. Jim[/quote][/quote][/quote]

So that means that the stored energy in the heavy flywheels WILL increase torque at the rear wheel?! Surely (my question was to rear wheel torque)?!

Ditto 'stroke' a longer 'stroke' is a longer lever isn't it... which goes right back to the definition of torque...

When using forced induction if everything could be perfect and you doubled the air pressure available- from 14.6 to 29.2 PSI -then theoretically you could double the peak torque. Since perfection is never achieved, the gains will always be less.

If the supercharger is capable of 1/2 bar boost, about 7.5 lbs then theoretically you could increase the torque by 50 percent. Jim

Fast Eddie said:

Heavy flywheels will not increase the torque of the engine. Of course the energy that is stored in a rapidly spinning flywheel may certainly help get a good launch in a drag race. Jim

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[/quote][/quote]

So that means that the stored energy in the heavy flywheels WILL increase torque at the rear wheel?! Surely (my question was to rear wheel torque)?!

Ditto 'stroke' a longer 'stroke' is a longer lever isn't it... which goes right back to the definition of torque...[/quote]

But the torque gained by a longer lever is precisely balanced out by the smaller piston size. Torque is produced by how much mixture is trapped and burned in the cylinder regardless of the bore stroke ratio. Jim

comnoz said:

Fast Eddie said:

Heavy flywheels will not increase the torque of the engine. Of course the energy that is stored in a rapidly spinning flywheel may certainly help get a good launch in a drag race. Jim

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[/quote]

So that means that the stored energy in the heavy flywheels WILL increase torque at the rear wheel?! Surely (my question was to rear wheel torque)?!

Ditto 'stroke' a longer 'stroke' is a longer lever isn't it... which goes right back to the definition of torque...[/quote]

But the torque gained by a longer lever is precisely balanced out by the smaller piston size. Torque is produced by how much mixture is trapped and burned in the cylinder regardless of the bore stroke ratio. Jim[/quote]

OK Jim, I did admit at the beginning that I struggle with this, so please humour me...

If torque is ONLY effected by "how much mixture is trapped and burned in the cylinder" then, to go back to the OP, what is the difference between torque and power? Why is it torque not simply linier to the RPM?

And... why does a heavy flywheel make a better street bike, in a (long stroke) Norton, than a light one?

I suggest torque also depends and on the burn rate of the fuel and the advance used with it. Jim Scmidt's long rods offer a longer 'rock- over' time which would also help. A lot depends on angularity of the rods as the pistons move down the bores. In that respect Jim's rods are slight backwards step if gaining more torque is your aim. If the cams and exhaust system you use dictate the use of a rev range that is too high to suit the rod/stroke ratio etc., you are defeating yourself. Once you enlarge the inlet ports to go top end, the process is not easily reversible.

I've watched Kenny Cummins' videos . His bike is really impressive - however that motor must be really expensive to behave like that. I'm a cheap-skate, and I stay away from big race circuits.

acotrel said:

I suggest torque also depends and on the burn rate of the fuel and the advance used with it. Jim Scmidt's long rods offer a longer 'rock- over' time which would also help. A lot depends on angularity of the rods as the pistons move down the bores. In that respect Jim's rods are slight backwards step if gaining more torque is your aim. If the cams and exhaust system you use dictate the use of a rev range that is too high to suit the rod/stroke ratio etc., you are defeating yourself. Once you enlarge the inlet ports to go top end, the process is not easily reversible.

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My understanding is that 'Torque' is / means 'turning force' (a given force on a given lever).

The power generated in the combustion chamber is simply power.

So, the bits that (any given power output) are connected to, translating this explosion into a turning force, MUST have an effect on the torque output...

Rohan said:

Some of these current big cruiser engines (HD, Victory, Kwikasaki) make max torque quite low down in the rev range.
But some go on to make some quite big numbers. Which is why they feel to have some serious mumbo, all loaded up with pillion and lots of gear, without needing to rev them...

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That is the whole concept of a cruiser engine. You can run all day in third gear and never shift up or down...torque up the ying yang and most of it developed at relatively low RPM. I'm looking at a deal on a Honda VTX 1300 right now and the engine torque curve is flat and peaks at 3000 RPM. It's one of the reasons my smaller V-Twins (Honda 750 and Kawasaki 800) are pushing it at 80 MPH. They run out of torque at about 70 MPH. Seems crazy but it's true. They are fun bikes but are limited.

"You can run all day in third gear and never shift up or down"...
That's what Vincent's are famous for... but I screwed mine up by fitting a 5 speed 'box !!

:shock:

Fast Eddie said:

The power generated in the combustion chamber is simply power.

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Power is a measure of work done.
Torque is what is generated in the combustion chamber.

And obviously modified by long rods, speed of combustion, etc etc.

And the gearbox is a torque multiplier = select a lower gear, get more torque (with more revs, but geared lower, to keep things equal).

Fast Eddie said:

"You can run all day in third gear and never shift up or down"...
That's what Vincent's are famous for... but I screwed mine up by fitting a 5 speed 'box !!

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Commandos are pretty strong just in top (4th) out in the country, unless you actually need to stop.
850s anyway.
Thats what strong torquey motors are all about...

Rohan said:

Fast Eddie said:

The power generated in the combustion chamber is simply power.

Click to expand...

Power is a measure of work done.
Torque is what is generated in the combustion chamber.

And obviously modified by long rods, speed of combustion, etc etc.

And the gearbox is a torque multiplier = select a lower gear, get more torque (with more revs, but geared lower, to keep things equal).

Click to expand...

I still don't get the 'work done' bit... but that is more than likely just my ignorance!

But at least we now seem to agree that it (torque) is not ONLY down the cylinder filling... it can be modified / effected by other aspects. Agree?

Rohan said:

Fast Eddie said:

"You can run all day in third gear and never shift up or down"...
That's what Vincent's are famous for... but I screwed mine up by fitting a 5 speed 'box !!

Click to expand...

Commandos are pretty strong just in top (4th) out in the country, unless you actually need to stop.
850s anyway.
Thats what strong torquey motors are all about...

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Quite so... but a Commando doesn't have superior cylinder filling to the latest Japanese (and other) sports bikes though does it? so its 'strong torquey motor' must surely be influenced by other factors?

So that means that the stored energy in the heavy flywheels WILL increase torque at the rear wheel?! Surely (my question was to rear wheel torque)?!

It will mean the stored torque of the flywheel is added to the engines torque. The torque will be applied to the wheel as long as the engine speed is dropping. As soon as the engine begins to gain rpm then the flywheel will be back to storing torque that is stolen from the engines torque.


Why is it torque not simply linier to the RPM?
Because the amount of mixture that is trapped and burned varies throughout the rpm range. IE a racing cam will reduce low speed torque because the valve timing reduces the effective volume of the cylinder.
As the engines speed increases beyond the measured torque peak then the cylinder does not fill as well because there is not enough time to get that much mixture into the cylinder.

And... why does a heavy flywheel make a better street bike, in a (long stroke) Norton, than a light one?[/quote]
Just because it is smoother and places less stress on the cases and anything else that tends to shake.
The reduced crank speed change from one stroke to the next also is easier on the drive train.

Many people prefer a light crank because it makes the engine sound more aggressive. If you go too light there is a point where power will be lost because there is not enough momentum to effectively absorb and release the power pulse from one power stroke to the next. The would be lighter than any of the generally available cranks.

Many racers prefer a heavier crank because it makes the power delivery smoother and easier to control in a traction compromised corner. It also make the bike easier to launch. Jim

Since a Commando has strong low down power in the rev range, and Jap sports bikes don't,
then the Commando must have superior cylinder filling - at lower revs.

Thats what long-stroke small-valve motors are famous for, after all....

Some 4 valve short stroke motors can be tuned for this too - but you don't commonly see this done.

A Norton produces a lot of torque in the midrange:

1.Because it is tuned for it. Intake, exhaust, and cams are built to fill the cylinders well at medium RPMs.
There is no point in trying to make torque on a long stroke motor at high rpms because any gains will just be lost to heat and friction because the piston speeds become too high.

2. Because compact well shaped combustion chambers burn faster and more efficiently than a large bore chamber.

3. Because short rods take advantage of the fast burn and apply their push to the crank at the optimum time to produce midrange torque.

comnoz said:

The Honda produces it's torque at high RPM and the Harley produces it's torque at low. Unfortunately for the Honda it's torque peak comes in too late to be of any use in 1/8th mile with stock gearing. Jim

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Very little use in 1/8 mile...peak torque on the Honda CBR occurs way up in the RPM range. The original CBR engine was quite amazing with 85 HP in a 600cc engine...which went to 100HP in the second generation. But the drawback is that you have to rev high to get the bike to do much...the video you posted shows that to some degree...the gen one Hurricanes that I have were geared such that you have to run around 7000 RPM just to get them to move...once up there they are quite fast but it's very different from the low end torque of Norton.

The Fireblade 1000 has the following specs:

HP 178.0 @ 12,000 rpm
Peak Torque 82.6 lbf·ft @ 8,500 rpm

The latest CBR600RR has the following specs:

HP 118 @ 13,500 rpm
Peak Torque 48.7 lb·ft @ 11,250 rpm

These small engines are quite interesting from an engineering standpoint.

Honda made a CBR250 4 cylinder in the late 80's into the 90's that reved to 20,000 rpm.

It had the following specs:

HP 45 @ 15,000 rpm
Peak Torque 15.9 lbf·ft @ 12,000 rpm

It's interesting how these engines get "weaker" as they get smaller, even while maintaining measured HP.

comnoz said:

So that means that the stored energy in the heavy flywheels WILL increase torque at the rear wheel?! Surely (my question was to rear wheel torque)?!

It will mean the stored torque of the flywheel is added to the engines torque. The torque will be applied to the wheel as long as the engine speed is dropping. As soon as the engine begins to gain rpm then the flywheel will be back to storing torque that is stolen from the engines torque.


Why is it torque not simply linier to the RPM?
Because the amount of mixture that is trapped and burned varies throughout the rpm range. IE a racing cam will reduce low speed torque because the valve timing reduces the effective volume of the cylinder.
As the engines speed increases beyond the measured torque peak then the cylinder does not fill as well because there is not enough time to get that much mixture into the cylinder.

And... why does a heavy flywheel make a better street bike, in a (long stroke) Norton, than a light one?

Click to expand...

Just because it is smoother and places less stress on the cases and anything else that tends to shake.
The reduced crank speed change from one stroke to the next also is easier on the drive train.

Many people prefer a light crank because it makes the engine sound more aggressive. If you go too light there is a point where power will be lost because there is not enough momentum to effectively absorb and release the power pulse from one power stroke to the next. The would be lighter than any of the generally available cranks.

Many racers prefer a heavier crank because it makes the power delivery smoother and easier to control in a traction compromised corner. It also make the bike easier to launch. Jim[/quote]

OK Jim, I'll ask a few more question, then back out of this. Its like being back at school where my lack of understanding held back the rest of the class... Its not fair to expect the rest of the forum to go at my slow pace here...!

When you said: "It will mean the stored torque of the flywheel is added to the engines torque"... I have been talking about rear wheel torque. Clearly, in what you say here, the rear wheel torque WILL increase by use of a heavy flywheel (even given the same cylinder filling)?

When you said: "IE a racing cam will reduce low speed torque because the valve timing reduces the effective volume of the cylinder" I agree Jim. And you have no doubt built more racing engines than me, but you will, I'm sure, have built engines, where despite the losses you mention here, peak torque is achieved BEFORE the engine comes on cam and the effects of the cam really start to work. What I don't get is, when that race cam does start to work, it surely does so by increasing cylinder filling... So why can that be, if cylinder filling is the only thing that effects torque, when peak torque has already been passed?

When you said: "a heavy flywheel make a better street bike... Just because it is smoother" Surely that goes against the comment about the torque of the flywheel being added to the engine? Surely this also helps make a better street (or short circuit) bike (where the throttle is used in short bursts)?

Like I said at the beginning, the more I think about this, the more confused I get... I shall desist from forcing my confusion upon innocent others now and return to the solitary confusion whereby I started ! :?