Has anyone ever done a dyno comparison straight cut gear vs helical gs1100e crank?

[maicojoe]

I was recently talking to an old GS racer about the pros and cons of a straight cut gear set versus helical gears on a performance GS1100e build. He said that at 11,500 RPM the straight cut gear was worth an extra 18 HP....Hmm, as I have never done a back to back test personally, I am wondering if any of you guys on here have done a test like this yourself, seen it in person? That's a huge amount for a 108 HP stock engine, or even say a 130-140 HP modified engine. He also mentioned something I never personally considered was that on a modified HP GS1100 or GS1150 engine in the 175-200 HP range is that there is a huge benefit to launching a GS at the strip, if your using a live clutch. That the stock helical gears will make your clutch very grabby, almost unusable. Makes sense, if I think about what direction the crank is getting wedged or shoved to.... none of these issues with a straight cut gear set. Also, is Pearson still doing GS cranks?

[Steve]

Also, is Pearson still doing GS cranks?

Can't answer your other questions, but as of a couple of months ago when I stopped at his shop, he was still very busy doing cranks.

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[maicojoe]

Cool, thanks. I need to get a crank done this winter.

[Nessism]

Helical gears are stronger and quieter but there is a thrust load created which can cause inefficiency. I read a couple of test studies just now looking to quantify the losses using helical gears and it seems they are better than 99% efficient in of themselves in terms of torque transmission. I have no clue how one could lose 18 hp due to the gears on even a race engine since that would constitute more than 10X the normal losses from the gears themselves.

[posplayr]

Frictional forces are rpm dependent and so the horsepower required increases as the 3rd power. 11500 is a bit beyond the normal street rpm range, but those internal frictional forces are rising fast considering a cubic law. So it all depends on where you start.
Straight cut gears also have friction just much less which means at high rpm they will be much less than the helical gears.

[maicojoe]

Nessism- Yes, that is my understanding also, in and unto themselves the helical gear set is pretty efficient. But when you start spinning it at such RPM's as a race engine or hot street engine the side thrust loads would seem to go through the roof like Posplayr is saying. I'm not much of an old Chevy or GM guy, but this got me thinking.... a quick and dirty way of testing straight cut versus helical would be to use a 1969 Chevy Z-28, with a race built 302 engine and a 4 speed transmission. Chevy offered a M21 and M22 Muncie 4 speed, the main difference between the two being the M21 has helical gears, the M22 has straight cut gear set. With a well built 302, with it being such a short stroke high rpm engine, it can spin to 10,000 rpm. Would be a simple transmission swap, apples to apples comparison on a chassis dyno. Come to think of it, I bet this is why or the main reason NASCAR still uses a modern version of the M22 transmission? More hp to the wheels, and much, much less heat produced, as they are running such high rpm continuous loads? Like Posplayr is saying, it's all to the 3rd power as the rpm increases. That could also be a huge benefit to our GS engines, is a decrease in oil temperatures with a straight cut gear set?

[posplayr]

The third power is the exact same model for wind resistance. You can not escape the manifestations of conservation of energy (re: friction, drag etc)

Force is proportional to Velocity squared(F=a*V*V).
Power is force times velocity(P=F*V), therefore power(e.g. horsepower) is proportional to the cube power of velocity(P=a*V*V*V).

A small difference at low velocity(RPM) is a huge difference at high velocity(RPM).

[headsbikesmopars]

I dont know how much Horsepower helical gears absorb, but I do know a local racer here that I have done work for picked up 6 mph in 1/4 mile going from helical gears to straight cut gears alone, no other changes. 1982 GS1100E , 1166 , nice ported head , 33 smooth bores , V&H drop in street cams , John Pearson did his crank and hub, EXCELLENT work ! His mph went from 128 to 134 . You are right Jim tremendous side loading so much that super hubs were the norm in the 80's . My Brother broke a hub in his '81 GS1100EX with only a pipe and a street head good running bike but no race engine . They're noisey but strong. Yes Pearson still doing the work, I talked to him couple weeks ago . If you are building anything above mild stock and going to be dropping the clutch super hub is minimum , straight cut gears would be better if you can take increase in noise , I dont even notice it any more .

Terry

[maicojoe]

I dont know how much Horsepower helical gears absorb, but I do know a local racer here that I have done work for picked up 6 mph in 1/4 mile going from helical gears to straight cut gears alone, no other changes. 1982 GS1100E , 1166 , nice ported head , 33 smooth bores , V&H drop in street cams , John Pearson did his crank and hub, EXCELLENT work ! His mph went from 128 to 134 . You are right Jim tremendous side loading so much that super hubs were the norm in the 80's . My Brother broke a hub in his '81 GS1100EX with only a pipe and a street head good running bike but no race engine . They're noisey but strong. Yes Pearson still doing the work, I talked to him couple weeks ago . If you are building anything above mild stock and going to be dropping the clutch super hub is minimum , straight cut gears would be better if you can take increase in noise , I dont even notice it any more .

Terry

Terry,
That information is absolutely spot on, real world confirmation.
Using a 1/4 calculator, which in my experience is about 95-99% accurate, I get 16 additional horsepower, to the wheel! That is huge.... your above bike is a very typical hot street GS1100e. It should take 125 HP to the wheel to go 128mph in the 1/4, with the bike at 550#, and rider at 200#. With the bike making 141 HP, that would give it a 134 mph trap speed.
16 extra HP on a 125 is a free (well, not for my wallet) 12.8% increase. What other single mod can we do to our bikes to get that amount? The guy that gave me the tip on the straight cut gear was Dick at Dick's Speed Equipment. Sometimes old racers might know a thing or two?

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[maicojoe]

And this is after with a straight cut gear set

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