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Assuming 215 lb/f of torque, geared for 238 mph top speed, this sucker provides 1350 lb. of thrust to push, say, 600 lb. in 1st gear (assumed 110 mph top) Other figures

Gear Thrust TopSpeed

1 1350 110

2 1100 136

3 925 161

4 800 187

5 700 212

6 625 238

Instant somersaults in the first 5 gears, just twitch the throttle a bit. Or lift your head at 150 in 3rd gear and increase the high drag a tad.



Is this scary, or what?
 

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Re. previous post. Yes, I know you can't apply 1350 lb. of thrust to a 600 lb. bike; it'll either flip or smoke its tires. It's the two to one excess of thrust in first gear that makes me wonder how you control all this. In my case, it's easy. I just don't buy one.
 

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supercharger drag is an issue if you're after peak power

If a supercharger gives you 50 additional hp but its drag takes away 10 leaving you with only 40 net extra, where a turbo would give you net 60 extra, you may deem the turbo a better choice. But in my opinion, on a motorcycle, 40 hp and linear throttle is far more important than 60hp and irregular throttle behaviour.

If you think you can build a turbo bike that will yield meaningfully more rear wheel output than a supercharged bike without lag showing up and while maintaining a smooth progressive throttle, you're very mistaken.

The issue in not that there will be lag. Lag by itself is not bad. What is bad about motorcycle turbos is the throttle behaviour. If you're in a corner, leaned over and you get on the gas for the drive out, you don' want the bike giving you more than you want it to. On a turbo bike, you simply don't have such precise control on the engine response. Bikes like the gixxer1k and ZX-12R are already very unforgiving of throttle misapplication. turbocharging them will compound the problem manifold.

No, I remain convinced that turbochargers are ideal for straight line acceleration only. For an all round use motorcycle, a low boost turbo might be OK, but I'll take a supercharger instead. I am not a big fan of superchargers, and on a car, I'll take a turbo over a supercharger most days. but not on a bike.
 

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A 230LB G.P. bike with 190 H.P. = 1.21 Lbs/H.P.



A 500LB Streetfighter with 350 H.P. = 1.43 Lbs/H.P.



A 600LB Streetfighter with 350 H.P. = 1.72 Lbs/H.P.



It looks like those power/thrust to weight ratios are already being exceeded, in modern G.P. racing.



We also KNOW that in addition to a greater power to weight ratio, a modern G.P. bike has:

a.) lower parasitic losses in the drivetrain, so it's actually going to put a greater percentage of it's engine's power to the tire.

b.) Has far less inertia to overcome.

c.) Has a peaky two-stroke, instead of tractable four-stroke power delivery.



I'm not saying that it's EASY or PRACTICLE to have a bike producing 2:1 thrust to weight. Just that it CAN be controlled and ridden, in an effective manner.

 

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Re: IT

Ya know, that sounds not un-like the powerband in a two-stroke!... uh-oh... there's that 'dirty' topic again! ;)

The reason I still ride 2-smokers is precisely for the rush at the powerband... I've often wondered if you could duplicate that with a turbo on a 4-stroker... hmmm... sounds like 'yes'?

And yes, whoever was saying that any sudden rush in power might upset cornering, yes... true.. but it is manageable... gotta be very careful w/the throttle. When I've let friends ride my strokers, they always start off and say "hey man.. where's the powwweeeeeRRRRRRRRRRR..OOOHHH SHIIIIII...."...

and this happens invariably while leaned over.. forcing them wide.

Hence, no one gets to ride 'em outside of a big parking lot the first time on. ;)

-James

P.S.: yes, before any 'turbo-bikers' out there tell me that their turbo-gixer-RR-ninja eats two-strokes... fine.. whatever.. I'm just making the point about the 'hit' and what it does in a corner if you're not used to it.
 

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What I would like too see is a very light motorcycle that is supercharged. Supercharging could be a good way to make a light motorcycle more powerful, so not only would it have great handiling, but it would be able to power wheelie in 3rd gear.



Maybe a FZR 400 with 140 hp? SV 650 with 120 hp? KTM Duke II with 110 hp?



What the heck, stick that 351 hp snowmobile engine in a YSR 50 frame!!! (OK that's a little much) An RS 50 frame then!!
 

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turbo is not like 2 stroke

in two strokes you merely have a very steeply climbing power band. On a high boost turbo bike, you have an engine whose off throttle to on throttle behaviour is not satisfactorily predictable and linear. its not about being peaky or not. Its about there being no time gap between when you ask the engine to do something and when it does it. Turbo bikes didn't take off (in sales, I mean) for a very good reason. And that reason is that a turbo bike needs its operator to ride around its imperfect engine response.

turbos are NOT an ideal solution on a motorcycle in tight corners.
 

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Re: turbo is not like 2 stroke

> turbos are NOT an ideal solution on a motorcycle in tight corners.

Yeah, well neither is V-boost, and the V-Max seems to be doing just fine. Musclebikes appeal to a very different group than SV650s or CBR600s.
 

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Sounds fun...but the re-inforced (heavier) chassis and bigger wheels/tires that would be required, not to mention the increased rotational inertias, etc... would destroy the handling anyway.
 

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1) You're talking lbs/HP; I'm talking pounds thrust to pounds of weight. The Hayabusa with a 150# rider and full of gas would be about 625# or 1.8 lb/hp. Add the rider and fuel to your figures and see what comes up.

2) I didn't say it was impossible to manage, just difficult. At no point can the rider open the throttle all the way on the supercharged Hayabusa without flipping or burning.

3) I'm talking street. On the track, it's a blast!
 

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That sort of goes for the Hayabusa, too. I assumed it had to be heavier than the stock one in my calculations. Look at that awesome rear tire !

But moderate boost on a light bike aimed at optimizing to power curve sounds wonderful to me. It doesn't hurt emissions or fuel mileage much and could actually smooth out power delivery with careful design.
 

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Motorcycle Land Speed Record kind of talk

I have noticed aerodynamic drag increases as to the cube of speed increases. Since horsepower is torque times speed, dividing speed out from both sides of the equation makes the torque required to drive a vehicle through tires on the ground go up as the square of the speed increase. Twice as fast requires four times the torque.

The normal maximum torque force a tire can exert against the ground is the weight on the tire times the coefficient of friction of the tire on the surface.

This has limited the top speed of all who have tried for that record.

I have a great solution, and a design that gets around this problem. If there is anyone else out there interested in actually for real getting the motorcycle unlimited speed record, please let me know if you want a solution that works and is not terribly expensive.
 

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Re: Motorcycle Land Speed Record kind of talk

I vote for six inch spikes in the back tire!

But seriously...

Isn't the limiting factor in speed records == drag?

I assume that traction isn't the issue at speed...or

is the real reason that the Hayabusa can't do

200mph stock is because the rear tire is

constantly slipping?

-- Michael
 

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Re: Motorcycle Land Speed Record kind of talk

dimensionally, he is correct. power = force x velocity. rotational power = rotational force (torque) x rotational velocity (rpm).

drag is a force that is applied to the vehicle by the air, and at the point the vehicle stops accelerating due to drag, the force that it is applying on the air is equal and opposite to the drag. What force is being applied? that is the power being transmitted to the ground by the tyre(s) divided by the velocity of the vehicle.

where does torque come into it? The engine produces a certain amount of torque that is multiplied or reduced by the gearbox and the differential. At the end, you have a torque being applied to the hub. torque divided by the tyre diameter gives you the force being applied to the ground at the contact patch.

As long as you have some traction, the limit to your maximum speed with by the power output and gearing. meaning torque.
 

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Physics 101, Fluids 101, and Thermo 101

Aerodynamic drag increases as frontal cross section increases, as drag coefficient (a measure of the vehicle's aerodynamic "slickness") increases, or as the SQUARE of the velocity increases.

Horsepower is a measurement of power (the rate of doing work.) Work is a measurement of energy expended (a force applied over a distance.) Torque is a essentially a measurement of force (how hard the engine can turn the tranny output shaft.)

Horsepower and torque are not directly related. If they were related mathmatically, it would be apparent on dyno curves.

So...

A vehicle's top speed is limited by where the horsepower, torque, and drag curves all cross.
 
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