how much hp or cubic inches needed

I have been told it takes 100 hp. to pull 4 mph.
HOw much for 6 and 8 mph
5-6k classes
thanks

Hp = Force x Speed. We can neglect wind resistance due to the low speed. Assuming the coeficent of friction of the sled on the track is constant as speed increases....we have:

Hp at 4 MPH = 100 HP.

HP at 6 MPH = 6/4 x 100 = 150 HP

HP at 8 MPH = 8/4 x 100 = 200 HP

As much as the checkbook will allow.

WOOOOOOOOOO!

Too many variables. Sled, track, chain
length, tires ,etc all play a factor.
I have seen 100hp tractors do good in 4
and 6mph. Also have seen not so good at
different track and sled.

Something I think is sometimes neglected is tractor choice for a certain class. Look at factory horse to tractor weight ratio, especially in mostly stock classes. If you are brand-blind, and I`ll use 4000lb class as just an example. Brand/model X weighs 3800 and is maybe 25 HP and stock cubes 240 and brand/model Y weighs 3800 and is 32 HP and 290 stock cubes, I`m picking brand Y, certainly to pull stock, and likely to modify too because there`s likely more room in the block to bore or stroke. Of course, most of us are brand loyal and that`s not always to your advantage if you like to win. Lol

Around here there are 550 cu in. Olly 88s pulling 3500 lb. classes--Good Luck!---Tee

Nail on the head! Indiana Ken. HP is a measure of the RATE of doing work. Work = force x distance . The horsepower measurement takes a look at the total work that was done over a given period of time and then says ok WHAT TIME PERIOD DID THAT WORK OCCUR OVER. One "horsepower" is doing 33,000 foot-pounds of work in one minute. That one horsepower can be made by doing a very small force at a tremendous speed or by doing a tremendous force over a very small distance in one minute. Here's a formula you can use to calculate the HP any shaft is producing anywhere in the world if it is rotating against some resistance that is measurable. Horsepower= Torque(force) x RPM(distance) all divided by the constant 5252. This can be used to measure the horsepower on your PTO shaft or a shaft sticking out of your living room wall . If the horsepower source you have doesn't have the correct speed or force you need to do the actual job you have to do, then you use a transmission to adjust the horsepower to get either the speed or force you need to get the job done. It takes the horsepower you have to work with and adjusts it to where it's made up of either more speed or more force while losing a tiny amount of the horsepower due to its own inefficiency within.