Horsepower?

Question

WOULD THIS BE THE WAY TO FIND HORSEPOWER IF I DIDNT HAVE A DYNO AND ONLY KNEW THE TORQUE THE RPM AND THE NUMBER OF CYLINDERS

YES I NO THERE IS A DYNO AND THERE IS A FORMULA BUT I THOUGHT THE FORMULA WAS WRONG BECAUSE FIRST I FOUND TWO TORQUExRPM/(5252 OR 5254)

SO HERE IS A SETTING

THERE IS A 4 CYLINDER ENGINE SPINNING AT SAY 60 RPM(I NO THIS IS NOT A REAL FIGURE) WITH 10 FT LBS OF TORQUE PER CYLINDER

SO THERE IS ONE FIRE OF THE SPARK PLUG EVERY 90 DEGREES ROTATION OF THE CRANKSHAFT AND EACH FIRE PRODUCES 10 FT LBS OF TORQUE SO IN A SECOND THERE IS 40 FT LBS OF TORQUE CREATED NOW MULTIPLY THAT BY 3600 AND U GET 144000 NOW DIVIDE THAT BY 33000 AND U GOT URE ANSWER SO 4.36 HP

IS THAT A CORRECT EQUATION?????????????????????( I REPEAT I NO THERE IS A DYNO I JUST WONDERING I M A VERY CURIOUS PERSON)

IF YOU CAN SUPPLY ME WITH SOME TORQUE GRAPHS AND CYLINDER NUMBER OF SOME CARS THAT WOULD BE GREAT AS WELL AS ANSWERING THIS QUESTION

SERIOUS ANSWERS PLEASE

Answer 1

whelp, that looks okay in theory, but there's a few holes in it. For starters, the number of cylinders is irrelevant when talking about horsepower - typically power is calculated from an engine, as a whole.

Horsepower is a measure of applying a force over a distance.

Torque = Work
Rate at which work is done = RPM
Horsepower = power

to calculate power, it's Torque * RPM / 5250

the 5250 is not some lame number outta nowhere either, it's actually arrived at by taking 33,000 (1 horsepower) divided by (3.14 x 2) = 5252.11312 - rounded to 5250 as a constant in the automotive industry.

Let's go a bit further with your calculation.

a 4 cylinder 4-stroke engine will fire one piston every 180 degrees of crank rotation, a 4 cylinder 2 stroke engine will fire one every 90 degrees of crank rotation.

so anyhow, based on what you originally said 60 RPM, with 10 ft. lbs of torque per cylinder would be 40 ft. lbs. of torque, at 60 RPM's

40 * 60 = 2400 units of work.

2400 units of work / (33000 / (PI *2)) = 0.465 horsepower

what I don't understand is where the multiplication of 3600 would come from, and then why you're dividing by 33000 - are you trying to calculate up 3600 RPM's? Unfortunately, you can't calculate torque based on a lower RPM - Torque is something that's created based on the efficiency of an engine, you'd have to calculate SO many variables (like Volumetric efficiency, engine size, etc) to figure out the torque produced by that engine, from that calculation, you'd be able to arrive at a reasonable horsepower estimation.

that's a VERY basic explanation. and when I say VERY basic, I mean very, ultra, bottom of the barrel explanation.

Answer 2

One test from one race doesn't show enough data in my opinion, but it's what we have soooo...... The 99 has a mediocre driver in it, and the 18 ran away from the field all night........ Look at the dyno results. Are you surprised? Horsepower does matter. As far as the 20 being ranked low in the test, the 20 was not terribly impressive that night so I'm not surprised. What has the 20 dyno'd all year??? We'll never know. One test doesn't show what's happened all year. This set of dyno's shows exactly what everyone has been saying......Toyotas do have more power. That wouldn't even matter, but the feeling is that the rules are in their favor to do exactly that. Any particular reason every manufacturer isn't allowed to run a cup version of their engines in this series? Not an excuse, just reality. Mark Martin fan....... Although it would truly show reality, the numbers you desire will never be made public.

Answer 3

There is a thing called a 'prony brake'. It works like a dyno by 'braking' the crankshaft and giving you the lb/ft reading at a certain rpm - therefore letting you calculate the horsepower. This would be crankshaft horsepower.
The number of cylinders don't matter - it's the torque delivered at certain rpm's.
There are engine analyzers available that can be plugged into the vehicle's OBD ports. You can make a test run with the analyzer plugged in and receive a lot of info, such as RWHP (rear wheel horspower - that is actual HP delivered to the wheels).

Answer 4

There is no equasion because all engine are built different. there is also the fact that you loose horsepower through the drivetrain(trans, rear differential). Therefore, your engine would have more horse by itself than whats calculated through the drive wheels(as on a dyno test)

Answer 5

Torque x RPM/5,252 so 40x60=2,400/5,252.=0.45 hp. That's according to "How Things Work" But realistically, I can't see an engine running at 60 rpm. But if you ran that tiny motor at 5,000, which it probably could, it would go to 38 hp That's almost 1hp per cubic in. which is a very efficient motor.

Answer 6

I am pretty sure that if horsepower could be figured with a mathmatical equation that the dyno would never have been invented.There would have been no need.