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The 4 Ways to Increase Rear Wheel Horsepower

4/25/2018

4 Comments

 
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  • 1 - Decrease losses from friction. This is hardest one to do and if successful will result in very minor gains...things like better quality oil, attention to internal tolerances etc.

  • 2 - Reducing rotational mass. Easier to accomplish and potentially much bigger gains but generally very expensive....things like lighter crankshaft and or flywheel, lightweight chain, sprockets and rear wheel etc.


  • 3 - Increase engine torque. This is the second hardest way to accomplish higher hp. This can be things like cylinder head porting, radius / multi angle valve seats, cams etc or simply increasing bore size. (no replacement for displacement)


  • 4 - increasing the engines max rpm while maintaining the same amount of torque or increasing the engine rpm quicker than torque is dropping. This is the easiest way to make more horsepower if you are not changing the engine displacement. This could be accomplished by pipe/intake length tuning, camshaft profile and timing(4 stroke), cylinder port timing (2 stroke) etc.


4 Comments

So your buddy has a Yamaha R1 with mods that makes 200 rear wheel HP you say....

4/23/2018

2 Comments

 
BMEP refers to the term "Brake Mean Effective Pressure" and is a theoretical but simple way to compare the performance of similar engines as well as evaluating "Performance Claims" of parts and or engine builders.  A engine designed for reliability that is naturally-aspirated and gasoline-fueled would normally have a BMEP of under 205 psi. Anything above that would require a very expensive engine development program. (ie: WSB,  Formula 1) The formula for BMEP (psi) = 150.8 x TORQUE  (lb-ft) / DISPLACEMENT (Cubic Inches).  Looking at our example above and plugging in the numbers -  The 200HP is at the rear wheel so we need to add a very reasonable 15% on top because BMEP is  calculated at the motor. So that means 230HP peak at the engine at aprox 12,000 rpm which calculates back to 100 ft lbs of torque at 12,000 rpm (HP = Torque X Rpm / 5252. So BMEP of thi phantom engine would be 150.8 x 100 / 61 = 247psi. Somebody is lying....                                                                                                                                                  

If we Plug in the numbers for a stock R! as pictured in the Dyno graph below we can see it is a much more reasonable figure of aprox 190 psi. If we use a BMEP number of 205 psi @ say 12,000 rpm you can see that a realistic potential HP for a modified R1 would work out to 83ft lbs of torque or 190 Hp and that is at the motor! Rear wheel would be aprox 15% less at 162hp.
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2 Comments

Why I may recommend Stiffer Fork Springs for a fork that already seems too firm.

4/11/2018

3 Comments

 
A lot of the non sport bikes models are under sprung from the factory. ie:cruisers
You actually have 2 springs, the fork spring and a "air spring" from the trapped air space in the fork. This air spring as the fork compresses is very progressive in its action.i f your fork rides low in the stroke because of too soft a fork spring you will be riding in the firmer part of the air spring. If the correct stiffer fork spring is installed the fork will sit up higher in the stroke and consequently sit and operate in the much softer part of the air spring. This will make the fork action plusher as well as help stability and cornering . This is also why you do not want to run air pressure in your forks if so equipped as this exaggerates the progressive nature of the air spring. If replacing fork springs you want a "straight rate" not a progressive rate as you do not want to add any more to the progressive nature of the air spring.
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3 Comments

    Author

    I have been involved in mechanics and motorcycling from a young age. I formed Cycle Improvements in 1981 and still have the same passion to learn today as when I started. Hope you find this blog interesting and educational.

    James Hunt

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