Like I said... you can get all kinds of technical. Yet all you have to know is: When it comes to our hobby, HP is how fast your engine can utilize it's muscle, and torque is a measure of the 'muscle' it has. Argue all you want, but that is how it pans out. Btw: Folks keep talking about HP as a power measurement and torque as accelleration... HP is a measurement time... how much work can be done in a given amount of time. Torque is a measure of strength (muscle). So it sounds like they are being used backwards of what they actually are. Accelleration is a product of work over time, HP is a measure of work over time. If torque was accelleration, my Powerstrokes would be really fast.
?? Ratio411, powerstrokes would have a great deal more parasitic loss and weight to pull. All else being equal, a car with more torque will accelerate faster? It makes sense the HP is how fast you make the power and torque is the measure of that power, I think? I'm thinking of a semi-tractor that has tons of torque but very little HP, comparatively. I think I'll consult a physicist!!
That's the physics definition from the book. Heres an example that isn't to hard: You have 2 engines, a 4 banger that produces 25ft/lb @ 10,500rpm and V8 produces 215ft/lb @ 1200rpm, after running the calculations you find both engines produce 49hp therefore doing the same amount of work in a given time. Also from some experiments when you have 2 cars with their respective gearing matching the power band and equal weights that are a 4cyl at 200hp@ 6000 / 73ft/lb @ 5000 to V8 at 100hp @ 3600 / 290ft/lb @ 1500 the V8 will take the lead off the line because it produces 82hp to the 69hp of the of the 4cyl then as we get going the 4cyl takes the lead as it has double the hp on the top end of the V8. then the they shift into second and the V8 pulls on the 4cyl again till they hit their hp band and the 4cyl pulls ahead further.
Torque is force applied, no work done. HP is work done. You can apply thousands of pounds of force without getting any work done, a lever trying to flip over a skyscraper. Plenty of force applied, but no movement. 1lb of force spun fast enough can equal 1hp. http://www.seight.com/torque.html The car with more hp will accelerate faster and hit the highest top speed, assuming other variables are the same. The car with more torque will feel more responsive to the throttle.
I don't necessarily buy into the theory that a numerically higher ratio always results in quicker acceleration. While it may be true in a great deal of situations, there are also times when too much gear can impede acceleration. This is particularly true in turbocharged applications. I have read many examples of turbo cars picking up a ton of et by switching to a numerically higher ratio. A motor with a lot of torque needs to be lugged to take advantage of its power.
Numerically higher ratio can hurt you just as bad as too low. 2.79:1, I'm halfway through second at the end of the eighth. 5.56, I top out drive before the end of the track. Everything has to match the components for the designed purpose or you have nothing.
Is'nt it at 5250 RPM"S that torque and HP are the same... Because of the numerical constant used in the math formula used to calculate HP from measured torque, a graph of an engine's HP and torque curves will always intersect at 5250 rpm. And because a chassis dyno measures torque and calculates HP from the torque measurement you can fool the dyno by changing tire sizes, tire air pressure, and rear gear ratio and come up with some pretty outrageous figures. That's what a lot of the magazines do when they test their buildups. I love this kind of $hit! :bananaman
Yea it's 5252. In an extreme way that's how 25ft/lb @ 10,500rpm is the same horose power as 215ft/lb @ 1200rpm I should have mentioned that I was assuming something was being done as in work
As Fred mentioned in his post, an engine with power adders often does better when it doesn't rev too quick due to gearing. Gives the cylinders more time to fill with boost if the engine is turning slower.
Yea it's 5252. Yeah, that's it. I knew it was somewhere around there. Now if I could just remember my own phone number...
Here's an analogy that I use. This analogy uses different physics like inertia, but its just intended to be demonstrative. Someone hit facts dead on... torque is force, HP is work. If nothing moves, there is zero hp being expressed, no matter how much torque you put on it. So, lets make an analogy. Lets say your engine is a hammer, and moving the car is equivalent to driving a nail into something. You could use a small hammer and swing it really fast to get the work you need, or use a huge hammer and you don't have to swing it as fast. The big hammer is like a low-rpm grunt engine, and the little hammer is like a little high strung four-banger. In another analogy, lets say you're swinging the hammer on a string above your head and it hits someone else's head. It exerts a force on their head when it hits. If you have a light hammer on that string, it will take a lot more speed to equal the force of impact that a heavy hammer would make. That analogy is an example of instantaneous work. Since engines are spinning, the equation is integrated from x=1 to x=rad and the resulting equation gives us a radial expression of work. It is from that equation that we extrapolate hp = tq x rpm/5250. The original equation was derived from the DIN hp extrapolation which used 5252, but the difference is minute. Torque is what we exert when we try to loosen a rusty bolt. HP is the work we do when we get it loose. Its a very abstract concept, but hp is basically torque over time.
I built my engine for torque. I agree, that I increased the horsepower somewhat. I did bore it .030 and put a mild cam, lift 512 & duration 230. Decided on the Edelbrock Performer RPM & Holley Street Avenger Carb 570 cfm. Stock cast iron heads. Put a 2500 RPM torque converter & 3.55 gears, in the 8" rearend. Makes for a whole lotta torque. Will put you back in the seat when the converter kicks in, & haul a$$ to boot. So, if I gave up horsepower for torque, then I'm happy with it. I prefer the feel of power. Then again, I just may put on some heads, that have been worked over (bigger valves, ported, etc). Also thinking about a mini spool 3.55 gears. We'll see what happens. Haven't made up my mind yet...I'll just keep reading this post, to help in making a decision about more horsepower...
