Sachs Madass 125 ?

[ProDigit]

Originally Posted by sendler

So using your logic a 650cc engine running at 6hp will always be more fuel efficient than a 125cc engine running at 6hp. But in reality this is not the case due to the increased heat losses in the larger combustion chamber and the increased pumping losses due to the throttle being closed more with the bigger engine. The first thing for you to learn about here is the concept of Brake Specific Fuel Consumption versus rpm and load.
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https://en.wikipedia.org/wiki/Brake_...el_consumption
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Not really true!
Each engine has a specific range where they run most efficient.
The larger the engine, the higher the MPH is that they run more efficiently.
If I where to gear a 650cc engine the same I would gear a 110cc engine, their most efficient range would be (my guestimate) at 3000RPM, about 60 to 80MPH. This would cause lugging of the engine.
But suppose your main goal is to continuously go at 60MPH, you would not choose a 110cc, not even a 250cc to be your main engine; but rather something like a 500cc.
The larger combustion chamber actually is much more efficient than a smaller chamber, as MORE of the heat is converted to motion, not less.
The cylinder walls of a small engine drain more of that energy than on a bigger engine.

*Edit: I just read jkv357's reply, and it's the same as what I wrote.
I'm not sure if you ought to ride a constant 50-55MPH, if a 110cc would have better MPG than a 250cc, but the 110cc should run at a much higher RPM to achieve this, and the life of the engine would be shortened, so a 250cc would make more sense. Larger cc engines might lug at too low revs.
I find at 50MPH, a 250cc should work just fine between 2500 and 3500RPM. A 350cc engine would work well between 2250RPM and 2750RPM. A 650cc engine would need to run at 1500RPM to have similar MPG, but that would lug the engine.

[sendler]

Originally Posted by ProDigit

The larger combustion chamber actually is much more efficient than a smaller chamber, as MORE of the heat is converted to motion, not less.
The cylinder walls of a small engine drain more of that energy than on a bigger engine.

Sorry but this is totally wrong. Larger combustion chamber areas will absorb more of the heat energy through their surface and waste it into the cooling system. And I believe that combustion chamber area is a bigger factor in heat absorption than swept area because peak temps are already dropping by the time the piston has moved down exposing the cylinder walls. So long stroke engines are more efficient than over square engines. And a single cylinder of the same bore/ stroke ratio and displacement has less surface area in the combustion chamber and is more efficient than a twin.
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Originally Posted by ProDigit

A 650cc engine would need to run at 1500RPM to have similar MPG, but that would lug the engine.

Now you are starting to get it. There is a big difference in efficiency throughout the operating range of an engine. Full throttle at somewhere just below the first torque peak can be nearly twice as efficient than a larger engine running at 20% throttle or running wide open at too low an rpm. Look at some BSFC maps and you will understand.
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This is why most vehicles have to Pulse-n-Glide in competition to get the best efficiency. They are way too powerful to keep a steady speed when operated in their efficiency band. The engines are way too large.
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Also keep in mind we are discussing the possibilities of ready to drive products. Not something theoretical that you wish to create in your lab.

[ProDigit]

Originally Posted by sendler

Sorry but this is totally wrong. Larger combustion chamber areas will absorb more of the heat energy through their surface and waste it into the cooling system. And I believe that combustion chamber area is a bigger factor in heat absorption than swept area because peak temps are already dropping by the time the piston has moved down exposing the cylinder walls. So long stroke engines are more efficient than over square engines. And a single cylinder of the same bore/ stroke ratio and displacement has less surface area in the combustion chamber and is more efficient than a twin.
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We're basically saying the same thing.
You mentioned that a twin is less efficient than a single cylinder.
That's basically what I have been saying.
Larger cylinders run more efficiently than smaller ones, as the surface area (cylinder walls) of a smaller engine are proportionally much larger than on a larger engine.
I mean to say, a single 250 is more efficient than a twin 250 (with 2x125cc), and more efficient than a 4 cylinder 63cc per cylinder.
Also more efficient than a 63cc at speeds where the larger engine isn't lugging.

[PeterS]

Originally Posted by ProDigit

We're basically saying the same thing.
You mentioned that a twin is less efficient than a single cylinder.
That's basically what I have been saying.
Larger cylinders run more efficiently than smaller ones, as the surface area (cylinder walls) of a smaller engine are proportionally much larger than on a larger engine.
I mean to say, a single 250 is more efficient than a twin 250 (with 2x125cc), and more efficient than a 4 cylinder 63cc per cylinder.
Also more efficient than a 63cc at speeds where the larger engine isn't lugging.

Despite that the Honda 50cc racers were twins ....and remarkably successful.
The Velobanjogent: Honda 50cc Racers…RC112,RC113, RC114 & RC115

[Grant-53]

A racing engine is opposite of a fuel efficient industrial engine in that it is developing power at high rpm.

[Andy_T]

The advantage of the Honda Innova 125 (or similar) is that it is lightweight, with a fuel efficient engine.

Where I live (Malaysia) I see tuned versions of that bike or similar (the kind of motorbike is historically best-loved by local riders), some of them (2-stroke overbored 125 cc versions) being clocked at 180 km/hour ... so I don't think (in fact, it is shown to me daily) that going more than 55 mph on such a bike is a major problem.

The Mad Ass, on the other hand, is a fun bike with incredibly cool design up to 90 km/h, I guess. I definitely would not think about going much faster with it ...

[PeterS]

Australia Post is now replacing it's fleet of CT110 "postie bikes" with a new version of the same design that is fuel injected .... quite similar to the Innova. It's not available to the public so we await second hand model's appearance.

[niky]

Originally Posted by Andy_T

The advantage of the Honda Innova 125 (or similar) is that it is lightweight, with a fuel efficient engine.

Where I live (Malaysia) I see tuned versions of that bike or similar (the kind of motorbike is historically best-loved by local riders), some of them (2-stroke overbored 125 cc versions) being clocked at 180 km/hour ... so I don't think (in fact, it is shown to me daily) that going more than 55 mph on such a bike is a major problem.

The Mad Ass, on the other hand, is a fun bike with incredibly cool design up to 90 km/h, I guess. I definitely would not think about going much faster with it ...

Highly-tuned scooter engines need more frequent oil changes and maintenance.

A friend once had one of those freak motors. Quicker than a V6 Genesis down the dragstrip. Needed a rebuild every few hundred running hours.

As a cost-saving daily driver, you don't want to be modifying and/or revving the hell out of these engines. They just won't last.

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But definitely doing 80-90 on a daily basis is no issue.

[cRiPpLe_rOoStEr]

Originally Posted by PeterS

Australia Post is now replacing it's fleet of CT110 "postie bikes" with a new version of the same design that is fuel injected .... quite similar to the Innova. It's not available to the public so we await second hand model's appearance.

Why are these bikes not available to the general public? It doesn't make sense.

[PeterS]

I have no idea ! Some arrangement between Honda and Australia Post?