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General Category >> Rubber Side Down! >> Interesting throttle position information
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Message started by Sandy Koocanusa on 08/13/08 at 17:57:28

Title: Interesting throttle position information
Post by Sandy Koocanusa on 08/13/08 at 17:57:28

I marked my throttle grip with masking tape the other day. I set it up to show me when I'm at the quarter, half, three-quarter, and WOT settings. I was interested to learn that I rarely open the throttle past 1/2. At 70 mph, while cruising, I'm right at half. 60 mph is closer to 3/8. 80 mph is about 13/16 or so. I did finally break 90 the other day, but I let gravity assist me a little. That was purely a fact gathering run, and not to be construed as an unlawful action without merit or legitimate purpose. ::)

It's probably no great revelation to some, but I think it is illustrative of the need for proper pilot jet size. If my bike is typical in this regard, that pilot jet is getting a lot of use, even on the back roads, and not just in town.

Title: Re: Interesting throttle position information
Post by Charon on 08/13/08 at 18:52:23

If the old rule is correct, saying power required goes up as the cube of speed, then half throttle gives about 80% of top speed. If top speed is about 85 mph, as suggested by some magazine tests, then half throttle is good for about 65. These are round numbers, so lets not have somebody correct me to eight decimal places. I am also assuming that half throttle actually gives half power, which may not be correct.

Title: Re: Interesting throttle position information
Post by Max_Morley on 08/13/08 at 19:22:29

Back when I was learning to tune up cars using a dynamometer (1965-66) we used 10 HP load for a 55 mph cruise for a full size vehicle, this was before use of radial tires and aerodynamic styling for the most part. I also ran a vacuum gage on my own vehicles then and that was about the same manifold vacuum at 55 in top gear, level road, as the 10 HP load on the dyno. So Sandy's numbers seem correct to me as far as throttle position in % is. Next time I think of it I'll throw my Snap-on scanner on my '04 Colorado and check throttle % at cruise. But it isn't near as much as you would think. Even on the '03 Savage sidecar tug I have lots of throttle turn left at 55 with the car and passenger, certainly an extra load between the car, its windshield and its passenger. It has a AMAL carb so is direct acting rather than the CV style that comes OE on the Savage. So pilot jet, idle mixture adjustment and needle jet and needle taper and position are used most of the time. Seldom do we use the screw in main jet, mostly the press in needle jet and needle. I do remember we used to have to change both of those parts on the B-i-L's Honda X/L 200 water changers bikes after 4 years or so as they would wear from the fuel that went by them. May be a consideration on ours as they accumulate mileage. Max

Title: Re: Interesting throttle position information
Post by Charon on 08/13/08 at 20:11:29

Coming at the thing from another direction, if you are getting 60 mpg at about 60 mph, which seems reasonable, you are burning about a gallon per hour of gas. Gas weighs about 6 lbs per gallon (the number used by aviators to figure airplane weight). A gas engine operating in the lab under really good conditions uses about .43 lbs of fuel to make one horsepower for one hour. In the real world it isn't unreasonable to assume .5 lbs per hp-hr, which is 12 horsepower hours per gallon of gas. So the Savage, burning 1 gallon per hour, is making about 12 horsepower. Magazine reviews seem to come up with about 25 horsepower for the Savage, so at 60 mph it is making about half of its available horsepower. That would imply a top speed on the order of 80 or so mph, again in reasonable agreement with the magazine top speeds of about 80-85 mph. Remember these are round numbers and approximations. It also implies total drag of about 75 lbs at 60 mph, if I didn't mess up my calculations.

Title: Re: Interesting throttle position information
Post by justin_o_guy2 on 08/14/08 at 11:27:38

neat reply Charon

Title: Re: Interesting throttle position information
Post by 07S40rider on 08/14/08 at 12:18:08

I think my head just exploded. :-?

Title: Re: Interesting throttle position information
Post by skatnbnc on 08/14/08 at 13:23:42

6D6A0E696D2F3439382F5D0 wrote:

I think my head just exploded. :-?

Ditto that ~ my head HURTS trying to figure out that technical stuff above! ;D

Title: Re: Interesting throttle position information
Post by Demin on 08/14/08 at 13:32:57

My calculator locked up. ;D ;D ;DJust went through all that in school(again).

Title: Re: Interesting throttle position information
Post by verslagen1 on 08/14/08 at 13:46:53

I twist the grip, I smile.
Twist it more, I grin.
WOT and I laugh maniacally.

That is all I need... and this teddy bear.

Title: Re: Interesting throttle position information
Post by eanon on 08/14/08 at 14:34:11

;D ;D ;D

Title: Re: Interesting throttle position information
Post by Robertomoe on 08/14/08 at 14:48:46

I think I understand :-?

It would make sense that we're only using half of our horses at 60 and all of them at 85. Doesnt the wind resistance about double between 60 and 80?