Horse Power?

Iowadiver

Registered
If you havn't gotten to know me and my posts yet, you'll soon learn I really don't care if people think I'm a jackass, poser, idiot or what not.... I ask questions I want answers to.... so without further ado...

Simply put, what is horsepower? Definition? I don't know much about the technicalities of the powerplant of the bike... how is horsepower calculated? How is it tested/determined? I hear riders talking about horsepower differences between the front and rear of the bike... how does this work? I may sound stupid, but I want to learn....

I'm sure I'll get some dumb ass responses to this post, but for those of you who once relied on others to gain the knowledge and abilities you now have, perhaps you might be able to enlighten me.

-Matt
 
Not a dumb question bro. But I'm not gonna answer it. The pros on here can answer much better and more accurately than I can. Props for havin the balls to ask a question that others may think as elementary
clap.gif
 
It starts out waaay beyond motorcycles...
It is defined as work done over time. Horsepower is 33,000 lb.ft./minute. If you were to lift 33,000 pounds one foot over a period of one minute, you would have been working at the rate of one horsepower.
 
I remember asking this when I was a kid. The answer I got was, that's how many horses it takes to stop that vehicle from full speed.

So with that said, if you open up a stock Busa on the expressway it'll take 160 horses to stop it.
ThumbsUp.gif


Personally though, I'd go with what brendanp said ...
 
Well there you have the specific definition..

In lay terms? the amount of work you can get out a gallon of fuel in the shortest amount of time
smile.gif
 
As far as testing it, you don't. Dynos can only measure torque. So the horsepower for an engine is determined based on a formula.

hp=(torque X RPM)/5252

So at 5252 RPM, hp = torque. The easiest way to raise the HP numbers for an engine is to increase its redline. I think the difference between the front and the back you are referring to is engine HP vs Rear Wheel horse power. Engine horsepower is measured at the flywheel. It is the gross hp that the engine creates. Rear wheel horse power is measured at the rear wheel. It is the net usable power after drive line losses.
 
Great info thus far guys... thanks... i'll be doing a bit of reading tomorrow on the suggested sites and I'll probably come back with some questions. Why am I asking all this beyond just wanting to be more knowledgeable? I think this will help me make better decisions as to what mods I make on the bike and what will be most beneficial to me... thanks again!

-Matt
 
Right, Mr Bogus! One thing my dad taught me about cars (which also applies to bikes) that i find to be VERY true:

"There's three things to consider when modifying a vehicle: Fast, Reliable, and Cheap. You can have two of them."
 
Right, Mr Bogus!  One thing my dad taught me about cars (which also applies to bikes) that i find to be VERY true:

"There's three things to consider when modifying a vehicle:   Fast, Reliable, and Cheap.  You can have two of them."
Or as my mechanic says regarding car repairs "good, fast, cheap, pick two."

cheers
ken
 
Great info thus far guys... thanks... i'll be doing a bit of reading tomorrow on the suggested sites and I'll probably come back with some questions.   Why am I asking all this beyond just wanting to be more knowledgeable?  I think this will help me make better decisions as to what mods I make on the bike and what will be most beneficial to me... thanks again!

-Matt
One thing to remember is that more HP is not always the best option depending on your riding needs. It is a drug thats hard to stop seeking though.
In the tight twisties more horspower could be a disadvantage depending on the rider. Less weight and moderate HP works better here.
If you're a daily commuter on your bike you might want to look for more torque in the lower to mid rpm's rather than topend redline HP.

One of the best bang for buck changes on the Gen I busa is to change the stock gearing. 2 up on the rear or 1 down on the front sprockets will make the bike feel much quicker and put the power closer to where most people will use it.
After that you need to let the engine breath better.
A PC and tune will get the most out of what is already there and make the busa much more fun and enjoyable to ride.

Just some things to consider...........
 
Great info thus far guys... thanks... i'll be doing a bit of reading tomorrow on the suggested sites and I'll probably come back with some questions.   Why am I asking all this beyond just wanting to be more knowledgeable?  I think this will help me make better decisions as to what mods I make on the bike and what will be most beneficial to me... thanks again!

-Matt
One thing to remember is that more HP is not always the best option depending on your riding needs. It is a drug thats hard to stop seeking though.
In the tight twisties more horspower could be a disadvantage depending on the rider. Less weight and moderate HP works better here.
If you're a daily commuter on your bike you might want to look for more torque in the lower to mid rpm's rather than topend redline HP.

One of the best bang for buck changes on the Gen I busa is to change the stock gearing. 2 up on the rear or 1 down on the front sprockets will make the bike feel much quicker and put the power closer to where most people will use it.
After that you need to let the engine breath better.
A PC and tune will get the most out of what is already there and make the busa much more fun and enjoyable to ride.

Just some things to consider...........
Two up on the rear is a pratical street mod.
thumb_up.gif
 The engine runs smoother at 60 or 70 mph on the highway. It also shortens the wheelbase for a little quicker turn in. The rear is easier to change as well.

Cheers
ken
 
On your question about the difference of HP up front VS rear. Well, if you measure your hp at the crank (that's where all manufacturers measure it --- and in a test bed where ONLY the engine is running without any attaching systems) you lose hp for each turning (ex: sprocks, chain, wheels, etc) item until you reach your new measuring point (usually the rear tire) ! There is a basic rule of thumb for motorcycles of a 10% loss from the crank to the rear wheel. Therefore a Busa with 165 hp at the crank would only have about 148.5 hp at the rear. Although with the Busa most stock bikes get in the 155 to 157 hp range for a 6% loss. Which is really good
ThumbsUp.gif
 
Front HP or brake HP or bhp is usually what manufactures like to quote for a couple of reasons.
1) It is a value of what the "engine" produces without regard to losses from the transmission linkage and it is an easy way of comparing various engines.
2) It will always be the highest HP number a bike can have, and HP number not comming from the engine will be lower due to friction losses.

It is not a real world figure because it is not the "usable" number of...as you put it "rear of the bike HP".

Rear wheel HP or rwhp or dyno figure HP is the "actual delivered to the ground" HP. Belt drive, chain drive, and then shaft drive (usually in that order) is what consumes most HP and lowers the brake HP down to rear wheel HP numbers.

Just make sure you are comparing the same type of HP #'s.
 
great call on the sprocket conversion... I did that on my R6 and noticed a good differnce in my street riding. Another question arises in regards to increasing horsepower... how do you figure out what increase in horsepower you have when you've done something like an exhaust system or what not... I saw the formula in one of the first posts, but how do you figure out your torque? Do you have to get on a dyno to have the figured out? I'd just like to be able to keep accurate measurement of the HP on my bike as I continue to make mods.

(I havn't yet checked those HP sites yet... late night last night "entertaining"... I should be able to read through them on sunday)
 
The only true way would be on a dyno and it would need to be the same dyno with the same guy runnung it to be fairly accurate to see how much each mod changed the HP numbers.

You can find some general numbers from others who have done the same mods that you want to try.

You wont accomplish much if you just put on a nice exhaust system but don't add more fuel to the mix with a power commander. In fact you'll probably lose HP from leaning out the a/f mix. From the factory most bikes already run lean to meet emmisions.

As an interesting note at a poker run there was a dyno set up, so me and another guy who had a busa with a 240 tire conversion ran ours. We had the same mods except for the tire. He lost over 10 hp from the added turning mass.
 
Horsepower is measured at the rear wheel, the crank, and the brochure.
laugh.gif


cheers
ken
 
As far as testing it, you don't.  Dynos can only measure torque.  So the horsepower for an engine is determined based on a formula.

hp=(torque X RPM)/5252

So at 5252 RPM, hp = torque.  The easiest way to raise the HP numbers for an engine is to increase its redline.  I think the difference between the front and the back you are referring to is engine HP vs Rear Wheel horse power.  Engine horsepower is measured at the flywheel.  It is the gross hp that the engine creates.  Rear wheel horse power is measured at the rear wheel.   It is the net usable power after drive line losses.
A good explaination of the 5252 number follows in the cut and paste from;
http://www.revsearch.com/dynamometer/torque_vs_horsepower.html


"Torque vs Horsepower

The word horsepower was introduced by James Watt, the inventor of the steam engine in about 1775. Watt learned that "a strong horse could lift 150 pounds a height of 220 feet in 1 minute." One horsepower is also commonly expressed as 550 pounds one foot in one second or 33,000 pounds one foot in one minute. These are just different ways of saying the same thing. Notice these definitions includes force (pounds), distance (feet), and time, (minute, second). A horse could hold weight in a static position but this would not be considered horsepower, it would be similar to what we call torque. Adding time and distance to a static force (or to torque) results in horsepower. RPM, revolutions (distance) per minute (time), is today's equivalent of time and distance. Back to horses, imagine a horse raising coal out of a coal mine. A horse exerting one horsepower could raise 550 pounds of coal one foot every second.

Here is an example of another way horsepower could be directly measured. Say you have a horse hitched to a plow. In the hitch is a spring scale (like a fish scale). The horse pulls the plow one foot every second and you see 550 pounds on the scale. That horse would be generating one horsepower.

We see horsepower can be directly measured. However there is a problem directly measuring horsepower of modern day internal combustion engines because they produce rotary motion not linear motion, and unless the engine is geared down, the speed at which they do work (time and distance or RPM) is too great for practical direct measurement of horsepower. It seems logical then that the solution was to directly measure torque (rotational force eventually expressed in pounds at one foot radius) and RPM (time and distance, i.e. distance in circumference at the one foot radius) and from these calculate horsepower. Torque and RPM are easily measured directly. Early dynamometers used a brake device to load the engine. A torque arm was attached to this brake's stator. The brake's rotor was coupled to the engine's crankshaft. A spring scale or other measuring device connected the torque arm to the stationary fixture holding the engine and brake. During a test the brake's application loaded the engine. Torque and engine rpm were observed and recorded. Click here for a description of how this happens on our dyno.

On modern day dynamometers horsepower is a calculated value. It's important to remember the dyno measures torque and rpm and then from these calculates horsepower. On the dyno it takes more water flow to the water brake to increase the load on the engine being tested. As the test engine's torque rises more water flow is needed. As the test engine's torque drops less water flow is needed. The dyno's water brake does not respond to Horsepower. Major adjustments to water flow are needed as an engine crosses its torque peak but none are needed as it crosses its horsepower peak. In other words the water flow to the brake during a dyno test follows the engines torque curve and not its horsepower curve. Torque is what twists the tire, prop, or pump. Horsepower helps us understand an amount or quantity of torque. (Torque + time and distance)

Now if we are measuring torque and RPM how can we calculate horsepower? Where does the equation HP=TORQUE * RPM / 5252 come from? We will use Watts observation of one horsepower as 150 pounds, 220 feet in one minute. First we need express 150 pounds of force as foot pounds torque.
Pretend the force of 150 pounds is "applied" tangentially to a one foot radius circle. This would be 150 foot pounds torque.

Next we need to express 220 feet in one minute as RPM.
The circumference of a one foot radius circle is 6.283186 feet. ft. (Pi x diameter 3.141593 * 2 feet)
The distance of 220 feet, divided by 6.283185 feet, gives us a RPM of 35.014.

We are then talking about 150 pounds of force (150 foot pounds torque), 35 RPM, and one horsepower.

Constant (X) = 150 ft.lbs. * 35.014 RPM / 1hp

35.014 * 150 / 1 = 5252.1

5252 is the constant.

So then hp = torque * RPM / 5252


Here is another way; Remember we know 150 foot pounds and 35.014 RPM = one horsepower

1hp is to 150 ft.lbs. * 35.014 RPM as X hp is to observed ft.lbs.torque * observed RPM

Example; We dyno test and observe 400 ft.lbs. torque at 5000 RPM

1 hp is to 150 ft.lbs. * 35.014 RPM as X hp is to 400 ft.lbs. * 5000 RPM

When we cross multiply X hp * (150 ft.lbs. * 35.014 RPM) = 1hp * (400 ft.lbs. * 5000 RPM)

X hp * (5252 ft.lbs. RPM) = 1 hp * (2,000,000 ft.lbs. RPM)

Divide both sides by 5252 ft.lbs. RPM

X hp = 1 hp * 380.80

X hp = 380.80 hp

Horsepower = torque x rpm / 5252

Here's an interesting bit of trivia; below 5252 rpm any engine's torque number will always be higher than its horsepower number, and above 5252 rpm any engine's horsepower number will always be higher than its torque number. At 5252 rpm the horsepower and torque numbers will be exactly the same."

cheers
ken
 
Back
Top