Drivetrain Power Loss

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DangerZone

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Thanks for all of the info. I didn’t reply sooner because the discussions quickly went over my head. I could in no way do the suggested math required and could only resort to trial and error which some posters suggested against. Also, although I could handle a little extra weight, the discussions led me to believe that a 5 foot shaft system would add enough weight/complexity to put the idea outside of the design mission. There is a design ( French I believe) that uses this setup with a BMW engine. It is a really nice looking aircraft and I’ll try to find pics of it and post. My design objectives required extremely light weight and unexcelled visibility. I could go with a swept forward wing but I really don’t like that idea. Thanks again.
There was a French short shaft homebuilt design driven by a Suzuki GSXR motorcycle engine and chain. The guy left the clutch inside the geared engine and used sprockets to achieve the final adjustment. Had more than 800 flying hours last time I've seen it.

Bear in mind also that chains&sprockets lose only 2 to 3% efficiency, while belts 10-20% and shafts 20-35% efficiency. Hence if you prefer some KISS solution, it might be wise to see if you can use some simple and proven concepts.
 

wsimpso1

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Bear in mind also that chains&sprockets lose only 2 to 3% efficiency, while belts 10-20% and shafts 20-35% efficiency. Hence if you prefer some KISS solution, it might be wise to see if you can use some simple and proven concepts.
Citation needed on those claims. I want to see what was being done to get those numbers.

I was a powertrain engineer with two major automakers over 23 years of experience. Those numbers are way off of anything we ever worked with. Just to get things onboard, in my career we used anything from a double compound to a quad compound planetary, a final drive gearset, six or more friction devices, usually with four or more open and dragging at a time, chains or gear transfer drive sets, a final drive set and either a single output shaft or two half shafts, meaning two to four universal shafts. On top of that we also had a pump drawing power from the engine to apply the friction devices and to lube/cool the internals and pump through the oil to air cooler. At high power settings and with everything warmed up, we regularly got 97% efficiency between flywheel and output ends of half shafts with all that hardware churning away inside. Element efficiencies higher than 99% had to be in place in all elements to get that level of performance. And that was typical from 1990 to 2015. That's 25 years, and I said 23 above. Yeah, I was out of the business for 20 months in there.

I suppose you could configure a test to show very low efficiencies - Cold system, oil bath, sliding contact gears, running at a just few percent of system capability on torque and power, yeah, losses could be pretty big fraction of the applied loads. I also suspect that you could get losses on those levels with worm gear drives intended to self lock when power is lost, but no one would run such a thing in a primary drive train of any vehicle. If your system had a high static drag and you deliberately ran it down near the static drag, you could even show 100% losses, but that is a bogus test. We are talking airplane power, almost never running less than 30% power, and most of the time at 70% or more, your efficiencies should be in the 98-99% range. Design the reduction drive and shafts for that power, and away we go with only a couple percent losses.

To specifics, we used oil spray lube on silent chains in automatic transmissions, which are also used in motorcycles, quads, etc, with losses well under 1%, as well as many others, typically 1/2% loss per chain and sprocket set. Belts have a long history in both accessories and drivetrains and are never more than about 1% losses or they would overheat the belts. Gears are typically well below 1% losses per mesh set unless they are designed to self lock. This might be important in control actuators, but you would never apply that sort of arrangement for turning a propellor. And shafts? The shaft itself is an elastic element as are the CV or Hooke joints at each end, which have rolling element bearings while moving through really small motions and so have tiny energy losses difficult to even measure.

There are lots of ways a gearbox and/or a shaft could give trouble, but efficiency is not really much of an issue.

Billski
 

DangerZone

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Citation needed on those claims. I want to see what was being done to get those numbers.
Motorcycles.

I'll skip the academic citations because there are real world numbers for certain motorcycle engines which used all three; chains, belts and shafts. The losses also varied from chain to chain, an o-ring chain has different losses than a chain without roller bearings. Feel free to check it out. Bear in mind that motorcycle shafts are much more complex than car/truck shafts, hence the higher losses.

The power increase (and losses) tests were usually done on dynamometers, which measured torque and horsepower.
 

DangerZone

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Are you sure? That seems like a lot of losses for a shaft .
It is a lot.

That is why most race motorcycles use chains instead of belts and shafts. Motorcycle shaft drives are slightly more complicated (than cars and trucks) because they need two bending mechanisms and have two 90 degree joints. They are also very heavy.

Back in the 1980s and 1990s, there were quite a few motorcycle engines which had both the chain and the shaft drive versions. The rear wheel shaft driven power was often 30% lower than those of chained bikes. Plus, the engines were modified to have lower max rpm for less vibrations and transmission through shafts. The dampers are different also, the chain dampers are simpler and lighter.

I still have a 1991 Suzuki GSX1100G motorcycle in my garage, it is shaft driven and has around 100HP at the rear wheel. I rode the same engine in a GSXR1100 frame, and it had between 135 and 145 ponies, and the whole motorcycle was almost a seventy kilos lighter (around 150 pounds) because of the chain. Just to get a perspective, the French manufacturer ViJa is making aircraft engines with these engine blocks.

 

AdrianS

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Motorcycles.

I'll skip the academic citations because there are real world numbers for certain motorcycle engines which used all three; chains, belts and shafts. The losses also varied from chain to chain, an o-ring chain has different losses than a chain without roller bearings. Feel free to check it out. Bear in mind that motorcycle shafts are much more complex than car/truck shafts, hence the higher losses.

The power increase (and losses) tests were usually done on dynamometers, which measured torque and horsepower.
So when you say 'shafts', you are including the two sets of gears that turns the transverse crank rotation to a longitudinal shaft rotation, then back to transverse to turn the wheel, right?

And the high-angle CV joint that takes the angle changes due to rear suspension travel?
 

DangerZone

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So when you say 'shafts', you are including the two sets of gears that turns the transverse crank rotation to a longitudinal shaft rotation, then back to transverse to turn the wheel, right?

And the high-angle CV joint that takes the angle changes due to rear suspension travel?
Yeah, and the vibration damper in the rear hub and the small clutch axis-wise, both are inside the shaft drive system. They all contribute to the losses, it would not work well without them. The motorcycle shafts are very reliable, but very heavy because of these little gadets. Remember the BD-5 long shaft issues? Without these little gadgets, there is risk to run into the same problems.

If someone would want a reliable AND LIGHT long shaft for a propeller up to 200HP, it would be wiser to use the existing motorcycle gearbox and 90 degree axle, ditch the whole shaft system and add a sprocket to the axle. This sprocket could turn the chain on the motorcycle main sprocket with the rubber damper on a long shaft. This combo is used sometimes on trikes and prop driven boats.

Using a long shaft without a clutch and damper would be a bad idea, for all the reasons Billski described well in his writings.
 

DangerZone

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Not able to quickly find the tail rotor shaft RPM. This would be critical to know if the plan was to use a Huey tail rotor shaft for aircraft propulsion. The rotor rpm in a helicopter does not vary all over the map as it does in a propeller aircraft. That would be another issue.

Does anyone know the tail rotor shaft rpm for typical helicopters?
This would depend on the rotor diameter. But if I remeber well from a UH-60 Blackhawk OH, the main rotor was around 250 rpm while the tail was at around 1200 rpm. Neither would be suitable for a homebuilt aircraft.
 

Pilot-34

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It is a lot.

That is why most race motorcycles use chains instead of belts and shafts. Motorcycle shaft drives are slightly more complicated (than cars and trucks) because they need two bending mechanisms and have two 90 degree joints. They are also very heavy.

Back in the 1980s and 1990s, there were quite a few motorcycle engines which had both the chain and the shaft drive versions. The rear wheel shaft driven power was often 30% lower than those of chained bikes. Plus, the engines were modified to have lower max rpm for less vibrations and transmission through shafts. The dampers are different also, the chain dampers are simpler and lighter.

I still have a 1991 Suzuki GSX1100G motorcycle in my garage, it is shaft driven and has around 100HP at the rear wheel. I rode the same engine in a GSXR1100 frame, and it had between 135 and 145 ponies, and the whole motorcycle was almost a seventy kilos lighter (around 150 pounds) because of the chain. Just to get a perspective, the French manufacturer ViJa is making aircraft engines with these engine blocks.

I own the 1979 crotch rocket. And like every other crotch rocket of that year it is shaft drive. I find it hard to belive that with the drive shaft giving up 20 percent of the power availability “Cycle” would have ever been called it a crotch rocket.
More likely to have been the “Lead Leg Log”
 
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wsimpso1

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That is why most race motorcycles use chains instead of belts and shafts. Motorcycle shaft drives are slightly more complicated (than cars and trucks) because they need two bending mechanisms and have two 90 degree joints. They are also very heavy.

Back in the 1980s and 1990s, there were quite a few motorcycle engines which had both the chain and the shaft drive versions. The rear wheel shaft driven power was often 30% lower than those of chained bikes. Plus, the engines were modified to have lower max rpm for less vibrations and transmission through shafts. The dampers are different also, the chain dampers are simpler and lighter.

I still have a 1991 Suzuki GSX1100G motorcycle in my garage, it is shaft driven and has around 100HP at the rear wheel. I rode the same engine in a GSXR1100 frame, and it had between 135 and 145 ponies, and the whole motorcycle was almost a seventy kilos lighter (around 150 pounds) because of the chain. Just to get a perspective, the French manufacturer ViJa is making aircraft engines with these engine blocks.
Before anyone else reads this pack of comparisons and thinks it actually means shafts and gears just waste energy by the ton, let's look a little deeper.

I looked up these bikes. GSX1100G is an upright posture cruising bike with big performance. Engine makes 98.1 hp at 7500 rpm, no rear wheel output in the lists I looked at. And the articles even mention the low max rpm and wide smooth power curve that suits easy riding styles. And it has a shaft drive so you do not have to fuss with keeping the chain lubed and regular replacements of chains and sprockets. This bike is not a canyon rocket, it is intended to be fun, but can be lazily ridden, two-up and go places. Suzuki sold fairings and bags for it so you could travel comfortably on this machine.

Then there is the GSXR1100, a faired sport bike requiring racing posture, and not really intended for more than one lucky individual at a time. Engine makes 156 hp at 10,000 rpm. To do that with the same basic engine means cams, induction, and exhaust tuning all aimed toward maximizing specific output, and usually drives torque way up the rpm band. Yeah, a peaky powerplant. Is this intended for easy riding? Nope. All out performance? Yep. Then the rest of the bike... much more compact set up, clip on bars, racing style fairings, yeah, a place is provided where a second person could ride along, but that is not what this bike is for. Looks more like a road racer than anything else. And you know what, the same spec sheet that says 156 hp engine also says 138 hp at the rear wheel. Somehow it is supposed to lose 18 hp or about 12% getting the power to the road.

So let's do what in the engineering world we used to call the laugh check. Let's see if that makes any sense at all.

First off, yeah, one engine is for cruising on a bike that will go when the throttle is twisted, and the other is intended to absolutely wow the bike geeks at the motorcycle magazines and turn in some impressive lap times at their usual race courses. And the difference shows, one has generous power for all around riding about with a passenger and bags, enough weight and length to make it cruise nice, and a power curve that makes for comfortable riding. The other, well, weight is driven down, the engine power is made at high rpm, and ultimate acceleration, braking, and cornering are optimized like a race bike. So let's not chalk up all that weight difference to excising a couple gear sets and a shaft and replacing them with sprockets and a chain yet. There are a bunch of differences between these bikes besides the final drive arrangement...

Next, do any of you have a concept of how much heat energy 18 or 30 hp is? If we lost 30 hp in a shaft drive system, which has a bevel gear set and CV joint at one end, another bevel gear set at the other, and maybe a rubber or spring isolator someplace, it would be a bunch. How much? splitting it to 15 hp on each end, one horsepower is 746 Watts, that is 11,190 Watts at each end of the shaft. Now let's get scale - a 60 Watt incandescent light bulb disappates about 90% of that 60 Watts as heat in a volume smaller than your fist, and it is too hot for you to hold in your hand. Maybe 50-60 F hotter than your hand. And that light bulb is about the same volume as the front gear set. 11,190 Watts divided by 54 Watts is 207. So that gear set would have to be disappating 207 times the heat of a light bulb out of about the same volume and across about the same surface area as your 60 Watt bulb. An 11000 F temperature rise! Yeah, it is attached to the metal housing of the engine/gearbox housings and will probably disappate heat more effectively so the temp would drop to a red glow instead of a white hot plasma, but still several times the temperatures that oil and seals and even heat treated steel gears and cast aluminum cases will stand. Simply put, exceeding about 1% losses has trouble living at high power.

Now let's look at the GSXR more closely. 18hp is still 12%, which is still an immense amount of heat concentrated on the chain and sprockets, the o-rings and lubricants will disaapear fast if that heat is even half going into the chain and then the air. Maybe some of it is going into the gear box. One or two meshes and four little bearings will use some energy, but we are proposing an order of magnitude more loss than is realistic. That is even a lot of heat lost to tire slippage on the typical dyno, but maybe a decent dyno session does cost a rear tire among other things.

What do I suspect? I think that marketing departments use horsepower of a perfect prototype engine on a dyno with cool air in, big suction on tuned pipes without mufflers, and fully warmed up systems for minimum viscous losses in both engine and gearbox. Maybe they even skip the gearbox. Then independant testers roll a complete motorcycle onto a dyno, fire it, and as soon as the oil temp gets off the peg, they run a couple speed sweep pulls. The engine and gearbox are still warming up, the tires slip a few percent on the roller, and they get a perhaps realistic number for this bike if you rode it fast right out of your garage on a steel roller instead of on flat pavement. Is 18 hp going away in that GSXR's drivetrain and at the tires? I highly doubt it. I suspect most of it was lost between marketing's brochures and getting a whole bike manufactured in volume and to the independant test lab. That's what happens with cars (23 years in the business of automotive powertrains). But losing that kind of power in a couple gear meshes and a cush joint or even on a chain drive? They would burn up the drive systems...

The claim fails at the laugh test level. Widely use engineering approaches are 1% or less loss of rated power per gear mesh or chain mesh. Belts run around 1% losses of rated power too. Well designed and developed systems can run quite a bit lower than 1%. Any system losing 2% per mesh or more is either:
  • Using sliding surfaces (worm gear drives and the like) or;
  • Is intended to self lock if input shaft rotation is lost, or;
  • The design team screwed up big, or;
  • Running really cold (think Antarctic ground vehicles);
  • Combinations of the above.
Billski
 

Vigilant1

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Thanks, Billski.
So let's do what in the engineering world we used to call the laugh check. Let's see if that makes any sense at all.
I was doing less sophisticated thinking along the same lines. Even in more moderate daily use, if our motorcycle engine is making 20HP to push a draggy rider and bike down the road at 65 mph, the idea of 20% loss to the shaft drive seems incredibly high. 10% at each end = 2 hp = 1500 watts of heat. After a trip on the highway, does the rear housing really feel like it is putting out the heat of a plug-in room heater on full blast? No, it is barely warm.
 
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DangerZone

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Before anyone else reads this pack of comparisons and thinks it actually means shafts and gears just waste energy by the ton, let's look a little deeper.

I looked up these bikes. GSX1100G is an upright posture cruising bike with big performance. Engine makes 98.1 hp at 7500 rpm, no rear wheel output in the lists I looked at. And the articles even mention the low max rpm and wide smooth power curve that suits easy riding styles. And it has a shaft drive so you do not have to fuss with keeping the chain lubed and regular replacements of chains and sprockets. This bike is not a canyon rocket, it is intended to be fun, but can be lazily ridden, two-up and go places. Suzuki sold fairings and bags for it so you could travel comfortably on this machine.

Then there is the GSXR1100, a faired sport bike requiring racing posture, and not really intended for more than one lucky individual at a time. Engine makes 156 hp at 10,000 rpm. To do that with the same basic engine means cams, induction, and exhaust tuning all aimed toward maximizing specific output, and usually drives torque way up the rpm band. Yeah, a peaky powerplant. Is this intended for easy riding? Nope. All out performance? Yep. Then the rest of the bike... much more compact set up, clip on bars, racing style fairings, yeah, a place is provided where a second person could ride along, but that is not what this bike is for. Looks more like a road racer than anything else. And you know what, the same spec sheet that says 156 hp engine also says 138 hp at the rear wheel. Somehow it is supposed to lose 18 hp or about 12% getting the power to the road.
...

What do I suspect?
...
Billski
It seems you missed the fact that these two bikes have the same engine. Same crankcase, crankshaft, valves, cylinders, cylinder head, pistons, piston rods and oil pump. The camshafts, carbs, and a few other parts are different, and the 90 degree angle output axle is unique on the shaft GSX1100G model. A friend of ours had a mighty fine tuned GSXR1100 which revved up to over 12k rpm and developed 184HP at the rear wheel. Then there are guys who add a turbocharger to this same engine and get more than 250HP at 8k rpm.

https://www.gixxer.com/attachments/dynorun_23_16psi-jpg.39378/

If you really think that this is only marketing hype based on some laugh thing and what you suspect, ok. If you can't understand why a motorcycle engine can have 156HP at the crankshaft and only 138HP at the rear wheel, that is also fine. People don't have to understand everything. If you can't understand something, it is sometimes easier to measure power and torque. Dyno measurements are quite exact, so why bother with complicated science if is easier and simpler to measure the power and torque and accept the facts?


All shafts, gears, sprockets, chains, or belt drives have transmission losses. Even motorcycle tires or aircraft props have losses. Some are more efficient at minimizing losses, some less. Those which produce minimal losses are considered more efficient than those which have huge losses. Shaft drives on motorcycles have huge losses, and all do not turn to heat as you speculated. It is supririsng that you worked in the automotive industry for so long and never had any experience with motorcycle power and torque transmission (losses).

The marketing claims of less than 1% losses in well designed and developed automotive systems are as credible as Volkswagen claiming they have low efficiency losses on the highway, or low emissions.
 

DangerZone

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I own the 1979 crotch rocket. And like every other crotch rocket of that year it is shaft drive. I find it hard to belive that with the drive shaft giving up 20 percent of the power availability “Cycle” would have ever been called it a crotch rocket.
More likely to have been the “Lead Leg Log”
Which crotch rocket do you have? I also have a crotch rocket from 1979, it would be nice to compare them...
 

wsimpso1

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It seems you missed the fact that these two bikes have the same engine.
Nope. I talked about the highly different power outputs in the second and third paragraphs of post 105, above. Here is some of the source data I found online:

Suzuki GSX1100G

Same base engine, greatly different state of tune. GSXR has much more peak horsepower and at much higher rpm while GSX has a wide torque band for easy riding. Those are tuning choices made to suit the product.

If you really think that this is only marketing hype...
I told you what I suspect based upon a long history of both seeing good data and seeing how some will embellish. There could be other sources... The rear wheel dynos could be way off too, but I am leaning more to the engines not making advertised numbers.

If you can't understand why a motorcycle engine can have 156HP at the crankshaft and only 138HP at the rear wheel, that is also fine. People don't have to understand everything. If you can't understand something, it is sometimes easier to measure power and torque. Dyno measurements are quite exact, so why bother with complicated science if is easier and simpler to measure the power and torque and accept the facts?
I spent 23 years in vehicle powertrain engineering. I do understand this topic. The overwhelming result is that the physics works just like they taught us in school. The folks that ignore that get surprises of the bad kind. I understand very well how horsepower can be lost between crank flange and wheels. I also understand that lost horsepower must show up as some other kind of energy. Take your pick: raised temperatures, sound, light, electro-magnetic effects, lifting weights. You have to put in fancy machines to do everything except convert energy to heat, lost energy goes into heat real easy.

As for dyno measurements being exact, please give it a rest. More than once I have received data from a purportedly well maintained million dollar double ended dyno cell calibrated within the previous three months that showed me over 100% efficiency for transmission stuff in between. One other time I saw test results from a transmission with pinned torque converter and pinned clutches locking the tranny in one gear, and the speed ratio reported from the dynos did not reflect the speed ratio of the gear locked in. We confirmed the gear ratio by hand before and after the test... Dynos are no better than the design and maintenance. They can be crappy indeed if the wrong numbers are put in the calibration files.

Shaft drives on motorcycles have huge losses, and all do not turn to heat as you speculated. It is supririsng that you worked in the automotive industry for so long and never had any experience with motorcycle power and torque transmission (losses).
So, tell us, just where does this large amount of lost energy go? Even when it propels the vehicle, it shows up as heat by churning the air that the machine just ran through. So what do motorcycles have that they can make power one place, express a bunch less of it someplace else and not be warming something in the middle?

You are not citing your sources and you are making outlandish claims that are unsupportable by even a basic energy balance. Citations are needed...

Billski
 
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Dan Thomas

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I'm with Billski on the heat from efficiency losses. Those losses cause heat and pretty much nothing else, and that heat has to show up somewhere. A 20-hp loss is nearly 15KW. The oven in your kitchen range has nowhere near that heat-generating capacity. Half of that, maybe. Any transmission or gearcase losing that much HP in heat would need some serious cooling. Big fins everywhere, or liquid-cooling jackets.

The physics and math are there and they don't lie. Rather inconvenient at times.
 

TiPi

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It seems you missed the fact that these two bikes have the same engine. Same crankcase, crankshaft, valves, cylinders, cylinder head, pistons, piston rods and oil pump. The camshafts, carbs, and a few other parts are different, and the 90 degree angle output axle is unique on the shaft GSX1100G model. A friend of ours had a mighty fine tuned GSXR1100 which revved up to over 12k rpm and developed 184HP at the rear wheel. Then there are guys who add a turbocharger to this same engine and get more than 250HP at 8k rpm.

https://www.gixxer.com/attachments/dynorun_23_16psi-jpg.39378/

If you really think that this is only marketing hype based on some laugh thing and what you suspect, ok. If you can't understand why a motorcycle engine can have 156HP at the crankshaft and only 138HP at the rear wheel, that is also fine. People don't have to understand everything. If you can't understand something, it is sometimes easier to measure power and torque. Dyno measurements are quite exact, so why bother with complicated science if is easier and simpler to measure the power and torque and accept the facts?


All shafts, gears, sprockets, chains, or belt drives have transmission losses. Even motorcycle tires or aircraft props have losses. Some are more efficient at minimizing losses, some less. Those which produce minimal losses are considered more efficient than those which have huge losses. Shaft drives on motorcycles have huge losses, and all do not turn to heat as you speculated. It is supririsng that you worked in the automotive industry for so long and never had any experience with motorcycle power and torque transmission (losses).

The marketing claims of less than 1% losses in well designed and developed automotive systems are as credible as Volkswagen claiming they have low efficiency losses on the highway, or low emissions.
sorry, you missed Billskis' point: there is no way a transmission set-up on a bike (or car/truck etc) can have more than a few % of power loss. There is simply no capacity to shed that generated heat without a cooling circuit and forced cooling. The only transmissions that do have forced cooling are automatic transmissions and some heavy-duty pullers. Most electric kettles are 2.4kW, I use that often to get the message across about heat energy and power. Having several of those kettles in your transmission system would cook the whole lot in no time.
 

AdrianS

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It seems you missed the fact that these two bikes have the same engine. Same crankcase, crankshaft, valves, cylinders, cylinder head, pistons, piston rods and oil pump. The camshafts, carbs, and a few other parts are different, and the 90 degree angle output axle is unique on the shaft GSX1100G model. A friend of ours had a mighty fine tuned GSXR1100 which revved up to over 12k rpm and developed 184HP at the rear wheel. Then there are guys who add a turbocharger to this same engine and get more than 250HP at 8k rpm.

https://www.gixxer.com/attachments/dynorun_23_16psi-jpg.39378/

If you really think that this is only marketing hype based on some laugh thing and what you suspect, ok. If you can't understand why a motorcycle engine can have 156HP at the crankshaft and only 138HP at the rear wheel, that is also fine. People don't have to understand everything. If you can't understand something, it is sometimes easier to measure power and torque. Dyno measurements are quite exact, so why bother with complicated science if is easier and simpler to measure the power and torque and accept the facts?


All shafts, gears, sprockets, chains, or belt drives have transmission losses. Even motorcycle tires or aircraft props have losses. Some are more efficient at minimizing losses, some less. Those which produce minimal losses are considered more efficient than those which have huge losses. Shaft drives on motorcycles have huge losses, and all do not turn to heat as you speculated. It is supririsng that you worked in the automotive industry for so long and never had any experience with motorcycle power and torque transmission (losses).

The marketing claims of less than 1% losses in well designed and developed automotive systems are as credible as Volkswagen claiming they have low efficiency losses on the highway, or low emissions.
I've spent most of the last 30 years designing dynamometer control systems.
When we built our first motorcyle dyno, we consistently measured 10-20% less power than the leading brand dyno.

Some research showed that they orininally 'corrected' the power readings to give the same number as claimed by the manufacturer.
Having done that, they couldn't go back - no one would be happy if their 1991 dyno gave lower power figures than the 1990 model.

The power readings given by a chassis dyno depend on many things, including tyre pressure, compound, how hard the vehicle is strapped down, and what gear it is run in. That's before you get to oil temps etc.
And don't get me started on 'crank HP' derived from the power measured at the rollers. :(

A chassis dyno is a very useful tool for tuning, but it's not a precision instrument. Especially since most have never been calibrated since they left the factory.

I have seen so many, many dyno charts that are obviously inaccurate. Enough to make me very cynical about the reading, unless I know both the dyno and the operator.


TL;DR - most bike (chassis) dyno charts cannot be trusted to be accurate.



ps As Billski said, you can't 'lose' power - the energy has to go somewhere. In the case of a chassis dyno, most of that 'lost' power goes into heating the tyre(s) and roller. And it's a lot.
 

DangerZone

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TThe xs1100 of course!
Excellent. I still own the 1979 chain driven croch rocket Z1000 in mint confition. It starred in an old movie called Mad Max in the 1970s. The chain drive allowed it to get more acceleration and outrun even more powerful shaft driven bikes, on less crankshaft power.

Some Yamaha XS1100 owners made shaft to chain conversions to get more acceleration and power. Just google XS1100 chain drive conversion. There are even companies which produce chain drive conversion sets. Ever wondered why would people go through so much hassle to convert an XS1100 to a chain drive?

http://www.motionlogics.com/contents/media/l_xs1100 chain drive main case 1.jpg
 

DangerZone

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I've spent most of the last 30 years designing dynamometer control systems.
When we built our first motorcyle dyno, we consistently measured 10-20% less power than the leading brand dyno.

Some research showed that they orininally 'corrected' the power readings to give the same number as claimed by the manufacturer.
Having done that, they couldn't go back - no one would be happy if their 1991 dyno gave lower power figures than the 1990 model.

The power readings given by a chassis dyno depend on many things, including tyre pressure, compound, how hard the vehicle is strapped down, and what gear it is run in. That's before you get to oil temps etc.
And don't get me started on 'crank HP' derived from the power measured at the rollers. :(

A chassis dyno is a very useful tool for tuning, but it's not a precision instrument. Especially since most have never been calibrated since they left the factory.

I have seen so many, many dyno charts that are obviously inaccurate. Enough to make me very cynical about the reading, unless I know both the dyno and the operator.


TL;DR - most bike (chassis) dyno charts cannot be trusted to be accurate.



ps As Billski said, you can't 'lose' power - the energy has to go somewhere. In the case of a chassis dyno, most of that 'lost' power goes into heating the tyre(s) and roller. And it's a lot.
Ok. According to your experience, do you think the same dynamometer could be so inaccurate to read 10% to 20% power difference for the same bike which has gone through a modification or engine/drive conversion?
 
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