80 HP at 8700RPM by Herb Becker

mdt-son said:

2. less engine torque is used on speeding up the flywheel,

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Since the spinning losses on a flywheel are quite low, any torque a flywheel picks up will be given back, sooner or later.
Flywheels merely influence how the torque pulses are smoothed out.

Ask any Harley rider, those big HEAVY flywheels are good for something.
HD big twin engines will pull from near idle at full throttle...

mdt-son said:

Fast Eddie said:

I am confused by your caveat 'if revs are kept constant' ... I would have thought that the primary effect of changing flywheel weight would be a change in the way the engine revs. My question is therefore what effect does this change in the way the engine revs, have on the dyno readings?

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In comparison with the heavy flywheel engine, the light flywheel engine will

1. speed up and decelerate the crankshaft faster (angular velocity),
2. less engine torque is used on speeding up the flywheel,
3. more torque will be available at the PTO as long as the engine speeds up and less as it decelerates, and
4. Provided the resolution and accuracy is good, the Dyno will show a higher torque and power during acceleration and less under deceleration of the crankshaft, if all other parameteres remain constant.

I hope this answers your question.

-Knut

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Yes Knut, I understand that and it makes sense to me. Thanks for finely finding my (low) level !!

mdt-son said:

Fast Eddie said:

I am confused by your caveat 'if revs are kept constant' ... I would have thought that the primary effect of changing flywheel weight would be a change in the way the engine revs. My question is therefore what effect does this change in the way the engine revs, have on the dyno readings?

Click to expand...

In comparison with the heavy flywheel engine, the light flywheel engine will

1. speed up and decelerate the crankshaft faster (angular velocity),
2. less engine torque is used on speeding up the flywheel,
3. more torque will be available at the PTO as long as the engine speeds up and less as it decelerates, and
4. Provided the resolution and accuracy is good, the Dyno will show a higher torque and power during acceleration and less under deceleration of the crankshaft, if all other parameteres remain constant.

I hope this answers your question.

-Knut

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Agree with most of your points which brings us back around to the link provided before showing what it can look like:

http://www.superchevy.com/how-to/en...to-add-hp-with-a-lighter-flywheel-why-weight/

Which responds beyond the initial question posed on the matter.

Of course we do not know exactly how much they reduced the actual rotational mass on the chevy (only total mass) as it appears they only changed to a lighter material for the flywheel yet the same disk and pressure plate was used. I disagree with what you are saying regarding the benefits are within the accuracy and resolution of a good dyno in the case of a Norton twin because when lightening a Norton crankshaft, most of the mass usually comes off the perimeter of the flywheel which will maxmize the reduction of rotational mass. I have felt and experienced the net results as have other; unfortunately I have not done the comparative dyno runs for a Norton twin.

I suppose if someone were ambitious enough and their college dynamics were up to snuff they could make some generalizations on a Norton flywheel and do a few scenarios on wind up time and torque required. It would be fun!

As for the virtues of heavy HD flywheels, take that to the modern Ducati list where they know a thing or two about torque, power and getting it all to the back wheel on asphalt in championship form.

mdt-son said:

4. Provided the resolution and accuracy is good, the Dyno will show a higher torque and power during acceleration and less under deceleration of the crankshaft, if all other parameteres remain constant.

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It would be interesting to see this documented anywhere for a Commando.
Torque - spikes and decays....

This has been asked previously, and no-one could produce anything.

I rcall that hobot produced a chart which claimed to show it for a V8 engine.
But when you looked closely, only 7 cylinders/effects could be counted !!
Maybe whoever faked it couldn't count....

Rohan said:

mdt-son said:

4. Provided the resolution and accuracy is good, the Dyno will show a higher torque and power during acceleration and less under deceleration of the crankshaft, if all other parameteres remain constant.

Click to expand...

It would be interesting to see this documented anywhere for a Commando.
Torque - spikes and decays....

This has been asked previously, and no-one could produce anything.

I rcall that hobot produced a chart which claimed to show it for a V8 engine.
But when you looked closely, only 7 cylinders/effects could be counted !!
Maybe whoever faked it couldn't count....

Click to expand...

Rohan,

I am pretty sure comnoz has this information to some level of detail for at least one crankshaft. Either I remember reading it here on Access Norton or maybe when chatting with him at the INOA annual or at some race venue. As I recall, comnoz was looking at dialing his fuel injection system in and it relied on a fairly accurate speed sesnor. That is all I have and hopefully Jim C. can chime in here on the matter as an item of curiousity.

A "fairly accurate speed sensor" and being able to monitor the acceleration and decay of the speed of rotation of the crank within the rev (or 2) are two VERY different things. So it will be interesting to see if anyone can produce something along these lines. Even comparing under heavy load and just cruising and just idling would be interesting to see....

Rohan said:

A "fairly accurate speed sensor" and being able to monitor the acceleration and decay of the speed of rotation of the crank within the rev (or 2) are two VERY different things. So it will be interesting to see if anyone can produce something along these lines. Even comparing under heavy load and just cruising and just idling would be interesting to see....

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Rohan, you seem to be too presumptuous. I recall comnoz was looking at crank speed differences between a few degrees of rotation. Close enough? Fairly accurate enough?

I don't know, I haven't seen the results or diagrams....

Anyone who can accurately record this at all can (easily ?) produce such stuff.
If it can't be exceptionally accurate, obviously it can't be shown...

Interesting logic there. For a minute there I thought there was a half way serious question there. My bad. :lol:

Until someone produces the data/graphs, its all just talk.

Good reliable data/measuring/interpretation of this is all over the shop, when you go hunting for it.
Not to mention senior moments on other threads...

Engine graphed at cranking speed. (not Commando, obviously).
It takes some serious sensors even to record that...


We diverge from hp somewhat though....

Rohan said:

Until someone produces the data/graphs, its all just talk.

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Yes, we hear you.

Plenty of online references regarding measuring of crankshaft acceleration so have at it and report back.

No one seems to have tried this on a Commando

Asked and answered. Maybe he will share with you if you ask. :lol:

Try a PM if you are sincere about this.

But I doubt anyone is interested in crankshaft acceleration at cranking speeds :roll:

Perhaps when you gain improvements in horsepower and torque on a dyno, the assumptions you make about their effect of on-circuit performance need to be based on experience ? I don't use a dyno, however if I had access to one I would be trying to correlate the output to the effect it had when the bike is ridden under race conditions. I suggest we all adapt to the machine to a large extent and if the motor is vicious we tend to ride differently to when it is smooth and friendly. I have not yet had a fourstroke-engined bike I could race competently on our Australian circuits using megaphones. A 500cc Manx Norton doesn't seem too bad, however a peaky twin cylinder fourstroke can be very bad for the nerves.

When I rode the 500cc Manx with the megaphone, I'd been racing my short stroke Triton for many years, so I was way ahead of it. I loved it. The same with the Seeley 850, nothing can happen to me in the same way it did with the Triton. A 750cc short stroke Norton commando fitted with megaphones should be a barrel of laughs. I'd ride it, however I would not race it.

Dances with Shrapnel said:

Asked and answered.

Click to expand...

Answered ??
The details were a little lacking....

Showing it at at cranking speeds is a very good initial comparison point.
And shows both the complexity of actually measuring this, and of interpreting the results...

Rohan said:

Dances with Shrapnel said:

Asked and answered.

Click to expand...

Answered ??
The details were a little lacking....

Showing it at at cranking speeds is a very good initial comparison point.
And shows both the complexity of actually measuring this, and of interpreting the results...

Click to expand...

This is too funny. Oh the humanity!!! The complexity of measuring this and of interpreting the results..... errr, not a moon shot nor is it rocket science for most but I understand where you are coming from.

For thoroughness, make sure to get a graph of crankshaft acceleration/deceleration while kicking the engine through and interpret that. :roll:

So, give us a quick rundown of all the salient points shown here, and why that might be....

Seems like we’re digging up the old discussion from several years ago regarding how flywheel mass affects HP and torque of an engine.

I believe the tangent we’re presently running on (variations in crankshaft angular velocity during a single Otto cycle) started with mdt-son simplifying his explanation, at Eddie’s request, where he stated that relative to a heavy flywheel engine “the light flywheel engine will…..

1. speed up and decelerate the crankshaft faster (angular velocity),
2. less engine torque is used on speeding up the flywheel,
3. more torque will be available at the PTO as long as the engine speeds up and less as it decelerates, and
4. Provided the resolution and accuracy is good, the Dyno will show a higher torque and power during acceleration and less under deceleration of the crankshaft, if all other parameteres remain constant.”

I’m quite certain that mdt-son’s 4th point simply referred to a full rip on a dyno and what occurs on the acceleration trip up and the coast down after the throttle is chopped. However some here have dissected the statement from this macro intent to the micro and are now examining angular velocity of a crankshaft over a single Otto cycle. We all know that significant variations in crankshaft velocity and torque occur during a single Otto cycle, so what is it that we are trying to unearth via this discussion of minutia?

The paper “Determination of The Engine Torque of a Four Cylinder Four Stroke Diesel Engine on the Basis of Harmonic Analysis of the Crankshaft's Angular Velocity” provided the following graphic illustrating variations in crankshaft angular velocity and torque that occur during a single Otto cycle. As the graphic clearly shows, the crankshaft velocity and torque vary significantly during a single Otto cycle. The authors attribute the higher range oscillations occurring in the measured velocity trace to elastic deformation of the crankshaft.



Our Norton engines will likewise have unique signatures of crankshaft angular velocity and torque that will depend on the given engine configuration.

In light of the above perhaps we can quit pissing in the ditch and get back on the road to constructive conversation. And with that, I’ll throw another target up on the road to get our focus off that target down in the ditch.

We’ve discussed much about heavy and light flywheels and how they affect HP, torque and dyno results, and IMHO have stated the large majority of the outcomes correctly. So here’s another one for the experimentalists in the crowd to try. It really makes no difference whether it is a heavy flywheel or a heavy rear wheel that adds mass to the system since any component subject to angular acceleration (shafts, gears, hubs, rims, etc) affects the system in the same way. So here’s your experiment, fit a water tire (filled with water instead of air) rather than an air tire on the rear of the bike and see how that affects the general feel of the bike. It’s a common thing, where allowed, in amateur flat track racing but you better be ready to chop the throttle in the vicinity of the starting line or you’ll be off corner #1 somewhere out in the weeds as the added wheel mass keeps right on flywheeling you along. Of course the benefit of the heavy wheel is that coming out of a corner the extra mass makes it more difficult to accelerate and break loose (better feel for the track) and the extra weight improves the tire contact patch on the track surface. A feather weight wheel/tire combo might be 12-15 lb and a water tire might be in the vicinity of 40-50 lb, so huge difference, especially with the extra mass positioned at such a large radius. While you’re doing that I’ll start generating that crankshaft torque/velocity plot for the air tire and water tire. Results should be absolutely titillating. Stay tuned I should have that wrapped up sometime in early 2019.

I picked up on your point that: ' It really makes no difference whether it is a heavy flywheel or a heavy rear wheel that adds mass to the system since any component subject to angular acceleration (shafts, gears, hubs, rims, etc) affects the system in the same way'.

Now, I'm not gonna do your water tyre experiment! But many modern bike mags have agreed on the results of fitting lighter carbon fibre wheels to bikes and all note, state, record faster acceleration as a result.

So that is another snippet of anecdotal evidence in support of the lighter crank idea.