# COMMUNITY : FORUMS : SQUARE PEGS

## HOW DO I DETERMINE HOW FAST AN AMOUNT OF HORSE POWER IS?

hey guys i was interested in making a go kart but i dont know how fast my 6 horse power engine will go. How do i determine how fast 6hp is, infact how do i determine how fast any amount of horse power is. p.s. : i dont care if it is in mph or kl/h.

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JasonC1851 year ago

if i had 8 horsepower to my new 2016 nissan maxima, how much faster and quicker will it be. I.E mph

rickick (author) 10 years ago
thnx
Bran10 years ago
If you could tell me how much your 6hp power will be pushing, I could figure it out and show you the formula.
10 years ago
Lemme clear that up, how much weight it'll be pushing.
rickick (author)  Bran10 years ago
about 200 pounds with the weight or the car maybe more plus the engine. and if you dont mind could you teach me the formula.
10 years ago
`Note:  I got carried away and typed a whole bunch of stuff that really doesn't matter.  If you want, you can read the first 2 lines and then skip down to the second paragraph, which is how to calculate the speed.  The first paragraph is to calculate horsepower.`

So if you and the car together equal 200 pounds (which I take is what you meant):

You'd have to go and convert 200 lb. to kg., which is 90.719 kg.

The formula to find the horsepower needed to go a certain speed is E=1/2*m*v2, or one-half times mass times velocity (meters/second) squared. The product of all that is the amount of joules needed. Now you need to know how many seconds you want it to take you to reach your speed. Let's use 2 as an example. You would divide the amount of joules by time (2 seconds, in this example) which would result in the watts needed. Then go here and scroll down just a bit and find Watts to Horsepower and do the math. There you go, that's the horsepower needed.

Now, we have to do all this backwards, since we need to know the speed.

So, with a 6hp engine and 90.719kgs of weight:

6hp is 4476 watts. If we still want to reach the speed in 2 seconds, we double this and get 8952, which is the joules. (Now comes the slightly more difficult part, it may help if you do this on paper next time.)

The formula was E=1/2*m*v2. We need to substitute which gives us 8952=1/2*90.719*v2. Start off doing simple things, like getting rid of the 1/2 by multiply 8952 by 2 (the reciprocal). Now we have 17904=90.719*v2. Divide 17904 by 90.719, which is 197.35667...=v2. Root it and you have you get 14.04... meters/second. Convert that over to miles per hour and you end up with a speed of about 31.4496 mph. I'd say that's a pretty good speed. The speed most likely will be a bit off, due to differing tire sizes, where you ride at, temperature, and the motor itself. Best of luck!
10 years ago
Hmm, formatting got a bit off. Oh well, should still be clear, hopefully.
jtobako10 years ago
It's also going to depend on your transmission ratio, max engine rpm and tire size.
rickick (author)  jtobako10 years ago
true i need to consider all of those factors when doing so