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Can anyone tell me if hp gains to weight gains is proportionate? For example if modifications were done to a 400lb. bike to raise the hp by5 would that be the same performance gains as raising the hp 10 on a 800lb bike?
 
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i forget what the ratio is... somebody said something like loosing X pounds is the equivalent of gaining Y HP. it's a direct correlation with static weight, but the advantages of saving weight is compounded when that weight is moving, such as with wheels, brake rotors, flywheel, clutch, etc...
 

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That's a good question, unfortunatly I don't have a good answer, but I would speculate that there would be no direct formula because accelerating is so much different than overall speed. Personally, I always put rotating weight 1st, unspung weight 2nd, overall weight 3rd, & HP last.
 

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If both bikes had the same engines, drivetrain, gearing and wheels and the only difference was the weight, yes. And only if you're comparing acceleration at relatively low speeds where the air drag is a small factor.
 

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... well, best way to lower weight is to go on a fast-food diet and get rid of any spare tires around the waist.
 

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Discussion Starter · #6 ·
... well, best way to lower weight is to go on a fast-food diet and get rid of any spare tires around the waist.
I guess if the bikes are carberated you could go on a low carb diet ;D I think i'm comparing apples and oranges. hp gains on my harley as opposed to a monster.If i don't go with a s4 " because of the radiator' a 900 will be my choice . I'm wondering how much of a difference 5 to 10 hp wil make on a monster as opposed to a stock bike.will the difference be significant?My harley has about 90hp at the rear tire and it's about 800lbs. :-/ It does rock when i hit the gas ;DThanks averyone for your imput 8)
 

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I'm just speculating on the configuration of your H-D, but if it makes 90HP at the rear wheel, I'm guessing that it's maybe a 100 cubic inch motor. If that's the case, it should make about 100 ft-lb of torque.

Nearly alll 2-valve motors follow this rule-of-thunb, making about 1 ft-lb of torque per cubic inch of dispacement. Really well built ones can do better, maybe 1.1 or so. The Monster 900 falls into that category, it's a 55 cubic inch motor, and makes 54 ft-lb of torque.
Assuming that you weigh 175 lbs for example, with the M900 weighing 425, that makes for a 600 lb package with 54 ft-lb of torque. That's 11.1 lbs per ft-lb. The S4 would have about 9 lbs per ft-lb.

Taking my SWAG of 100 ft-lb of torque on your H-D, and 800 lb bike with 175 lb rider, that's 9.75 lbs per ft-lb.

So if you were on your H-D, and your identical twin brother was on the M900, and you were both rolling down the road at the same speed and RPM, your H-D would win the roll-on contest. If your ITB was on the S4, he would win.

This is all a very simplified comparison. The character of the engine comes into play to a very large degree in how the bike feels. I suspect your H-D doesn't rev beyond 7000, peak power at maybe 5500, and peak torque at maybe 3000. The M900 revs to 9000, peak Hp at 8000, and peak torque at 6250. The S4 revs to 9500, peak power at 8750, and peak torque at 7000. The Monsters are a totally different breed of cat from the H-D.

For the roll-on contest, either Duc could be going the same speed as the H-D, but in a lower gear turning more RPM, and thus make more torque at the rear wheel, and then win the roll-on.

My essentially stock S4 makes a shade over 100 HP at the rear wheel, and I very rarely wish for more. I would probably have been satisfied with the 900, but my last streetbike was a XV920R, so I'd already done the air-cooled 2 valve gig, and wanted more scoot and a modern 4-valve motor.

Different horses for different courses......
 

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80-90 HP on an air cooled monster will blow your mind (& you'll run circles around an S4). And Daffy....how many of those diets have you been on?....what are you, about 130 soaking wet??
 

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< sound of gloves being thrown onto the ground > ;D

I agree with what Norm said, except the 'running circles' part... :-/ My S4 is a little heavier than a 900, but not 10 HP worth, and 90 HP 900's are pretty rare. That is a pretty expensive upgrade, from the little I know about 2-valvers.

Maybe someday I'll do a little drag race against one...


P.S. AFAIK, Daffe's closer to 100 lbs.
 

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... I've weighed in as light as 95 lbs and as heavy as 110. I hover at around 105 (with about 5 lbs of clothes/shoes). If I eat 1 meal a day for about 2 days, I can get down to 95 lbs. Guessing motorcycle gear is around 10 - 15 lbs. That's giving me around 120 lbs max. AND if I go with about 1/4 of a tank of fuel in the monster, it's a pretty light machine.

If I weighed in at 130, I'd be a real porker... potbelly, and the dreaded dickiedo disease.

FWIW, anyone can run circles around the Space Shuttle if it's sitting on the tarmac.
 

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" thingyiedo disease " ??? ??? ???
---------------------------------

No worries on my S4, it's got more steam than I can use 99% of the time.
 
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Most 900's dyno runs that I have seen are closer to 58-59 ft lbs of torque. I've seen 'em as high as 69! Modded of course....
....I'm with Norm in that I would take an air cooled 2V anyday, just to whup S4 butt! :p, ;D
I don't believe the bike will run circles around one though, I believe the rider can however. ;D
 

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Well, I've never ridden with Norm, but I'm pretty confident that on a twisty road, he'd be out of my sight in short order. I've got FHE that you can do that to me with your 900.

On a straight line run where HP is the only weapon, I'm equally confident I'd sneak away from any air-cooled Monster.

I've seen Alex's dyno results of his '900' 2-valver, and it's very impressive. He's invested a lot of love in his motor, and it shows.

FWIW, the torque figures I gave were directly cribbed from ducati.com....
 
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Nick....I was trying to stir up the pot...... ;)
I don't know what you are talking about..I can't keep up to those damn S4's...I hate you guys!
 

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Ahhh.....it's always nice to stir the pot!! But, remember, I'm just a crippled old man, my fast days are behind me. But....should I throw out the $1000 gauntlet to REALLY stir things up?? And..... don't forget the always appropriate "water cooled monsters are for gurley men"!!!
 

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The $1000 bet was awhile ago to a guy who thought his Monster could be a Japenese 600. I thought it would be a good way to pick up some easy money. I'm not too sure I'd be that brave about a 900 beating an S4 - maybe $10??
 

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Well. That was interesting....
 
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Ahhh.....it's always nice to stir the pot!! But, remember, I'm just a crippled old man, my fast days are behind me. But....should I throw out the $1000 gauntlet to REALLY stir things up?? And..... don't forget the always appropriate "water cooled monsters are for gurley men"!!!
too funny.....I got another ten Norm....
 
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