Rear wheel horsepower

[1948man]

The '83 GS 1100GL specs show 94 horsepower stock. What would the rear wheel horsepower be? Is there a guestimation of a percentage of loss in the shaft assembly etc?

[1948man]

Okay, found approx 15% loss somehwere. Is that a good ballpark?

[Nessism]

The shaft drive will chew up some power for sure, but not sure how much. Other thing I'd say is I doubt that engine makes 94 hp. Closer to 84 I'd guess.

[posplayr]

Okay, found approx 15% loss somehwere. Is that a good ballpark?

that is the number for chain drive; likely much less for shaft drive.

Power is measured at the output shaft so we are talking about the difference between chain vs. shaft with a certain about of bearing and rear tire resistance added in.

Since a chain is so relatively efficent, I would figure no more than 1/2 is in the chain or 7.5%.

If the shaft was twice as lossy as the chain then that would put you at 7.5+15=22.5% for a shaft

[7981GS]

Typical drive line loss is 15% with a driveshaft.
Typical loss with chain and sprockets is 5-10%.

Daniel

[posplayr]

Typical drive line loss is 15% with a driveshaft.
Typical loss with chain and sprockets is 5-10%.

Daniel

I guess I nailed it then

15% loss is the typical derating for engine hp between output shaft and rear wheel.

[Graham]

Factory brochure had 92hp @ 8000rpm and some articles have 98hp @ 8700rpm and 94hp @ 8500rpm for the GS1100G, GL, GK.


Sure someone didn’t pull that 15% out of a hat? I’d like to see some real test results.

[bobthebiker88]

the difference is that one number is measured at he CRANKSHAFT, not output. the other is wheel.

you also have to factor in different dyno setups configured differently in ways, or generally inaccurate.

[posplayr]

Factory brochure had 92hp @ 8000rpm and some articles have 98hp @ 8700rpm and 94hp @ 8500rpm for the GS1100G, GL, GK.


Sure someone didn’t pull that 15% out of a hat? I’d like to see some real test results.

Yea, if that G has a chain it would probably put down 150 RWHP

[1948man]

I just retired from Fedex 11/30, but I had a customer with a dyno. He builds dragsters and competes on a national level. I took my bike to him Monday and it dynoed at 72 rwhp. I guess if Ed is right with the estimate of 84 or so, the 72 rwhp is in line with he expected loss. I was wanting to see how my engine was doing and decide if I want to keep working with the bike or get something else. He surprised me by saying the engine sounded great and was not far off at all. It was a little rich at the bottom and a little lean above 7000 rpm but would pull to 9000 rpm. My tank is spewing some small rust particles and I have an inline filter which could cause a slight starvation at high rpms. The tank has a lousy PO Kreme job so I'm dreading trying to strip it and redo. I have shimmed the valves, soaked and cleaned the carbs and synced the carbs with a Morgan Carbtune. The needle has no spacer (PO removed). I tried putting 1 or 2 of the little washers in but it balked in mid-range.I haven't done the coil relay mod. I think I can justify getting a dynojet kit but am looking at a Bandit today and may try to trade my 'Cade towards it so Who knows? Thanks for the replies.

Jim M

[posplayr]

I just retired from Fedex 11/30, but I had a customer with a dyno. He builds dragsters and competes on a national level. I took my bike to him Monday and it dynoed at 72 rwhp. I guess if Ed is right with the estimate of 84 or so, the 72 rwhp is in line with he expected loss. I was wanting to see how my engine was doing and decide if I want to keep working with the bike or get something else. He surprised me my saying the engine sounded great and was not far off at all. It was a little rich at the bottom and a little lean above 7000 rpm but would pull to 9000 rpm. My tank is spewing some small rust particles and I have an inline filter which could cause a slight starvation at high rpms. The tank has a lousy PO Kreme job so I'm dreading trying to strip it and redo. I have shimmed the valves, soaked and cleaned the carbs and synced the carbs with a Morgan Carbtune. The needle has no spacer (PO removed). I tried putting 1 or 2 of the little washers in but it balked in mid-range.I haven't done the coil relay mod. I think I can justify getting a dynojet kit but am looking at a Bandit today and may try to trade my 'Cade towards it so Who knows? Thanks for the replies.

Jim M

Your numbers track very closely to a 22.5% loss for the shaft drive as compared to 15% for chain drive. Given the folloing data:

gs1100E: 108 horsepower stock; dynoed at 92 rwhp(this a nominal number reported here at GSR by a few members for stock bikes)

gs1100gl:94 horsepower stock; dynoed at 72 rwhp

You will find that the following formula applied to the data yeilds the following losses 14.8% 23.4%

%Loss = 1-Dyno/Rated

Using the previously specified parameters of 15%(chain) and 22.5%(shaft) you get the folloing calculated RWHP numbers which are very close.

Chain ---------SHAFT DRIVE

estimated ----estimated

108 ----------------94 hp

91.8 -------------72.85 RWHP
15.0% ----------22.5%

[Graham]

Your numbers track very closely to a 22.5% loss for the shaft drive as compared to 15% for chain drive. Given the folloing data:

gs1100E: 108 horsepower stock; dynoed at 92 rwhp(this a nominal number reported here at GSR by a few members for stock bikes)

gs1100gl:94 horsepower stock; dynoed at 72 rwhp

You will find that the following formula applied to the data yeilds the following losses 14.8% 23.4%

%Loss = 1-Dyno/Rated

Using the previously specified parameters of 15%(chain) and 22.5%(shaft) you get the folloing calculated RWHP numbers which are very close.

Chain ---------SHAFT DRIVE

estimated ----estimated

108 ----------------94 hp

91.8 -------------72.85 RWHP
15.0% ----------22.5%

I remember something about factory hp being taken at the output shaft of the transmission (old cycle magazine article).
How can compare chain and shaft hp loss without having the same gear ratio and tire size or having a true engine hp? Got to have the engine hp without chain and shaft and rwhp from the same bikes not factroy hp from a new GS. Apples and oranges? And if ratio and tire size aren’t the same between bikes your not comparing chain to shaft.
Estimate is like an opinion, everyone has one.

[posplayr]

Estimate is like an opinion, everyone has one.

and yours is showing,


it is unbelievable how you twisted that argument around.

Hp and torque are functions of RPM. Gear ratio or load doesn't matter.

What is even worse is your completely avoiding the data

[salty_monk]

My skunk was noticeably quicker than my 1000g with similar setup...

[posplayr]

My skunk was noticeably quicker than my 1000g with similar setup...

But Dan your two bikes were different colors so that would invalidate any comparison