Torque ∝ HP

I'm waiting around at work for some guys to finish some stuff, so I thought I'd expound upon something that always bothers me as an engineer.

Torque and Horsepower, in an internal combustion engine, are entirely proportional. One doesn't have a torquey engine or an engine with a lot of horsepower and no torque. The torque is what makes the horsepower.

The two are related by multiplying Torque at a given RPM by the RPM, and then dividing by 5252. The number 5252 being a series of unit conversions to get from useful units like ft-lbs, to ridiculous units, like Horsepower (which is related to the amount of work done by a weak little pony lifting a bucket out of a well, not kidding, no idea how that's the unit we picked as our standard). This is why dyno's that show torque and hp on the same scale always cross at 5252 rpm.

So when you say you want a motor with a lot of torque, but aren't worried about HP, what you're really worried about, is moving your engines performance, such that peak torque occurs at lower rpms, instead of higher rpms. Which is great for street use, because it gives a nice even powerband. i.e. if your torque starts high and drops off as RPMS increase, you'll have relatively flat power, which is nice and predictable, and doesn't leave you stalling at every stoplight and trying to hold on for dear life when you hit 5k on the tach.

For racing, since you're staying at high rpm anyways, you can take advantage of that multiplier in the relationship between HP and Torque, by tuning the engine such that it's able to run more efficiently (and hence produce more torque) at higher rpms. This leaves you with virtually no HP in low RPMs, which is why people say high HP bikes aren't "streetable" because it's a pain to try and ride them through traffic and always have to be in just the right gear. But if you make 50 lb-ft of torque at 6000 rpm instead of at 3000, you're making twice the power, so for racing it's just what you want.

That said, I don't really get bothered by people using the terms torque and hp to talk about low rpm power and high rpm power. Just thought maybe someone could learn a little more about how motors work.

Have fun guys.

:huh:

:dry:

So whats the problem guys?
For once I find myself agreeing with an engineer instead of screaming at one on a jobsite asking where he got his degree! :woohoo: :woohoo: :woohoo: :woohoo: :woohoo:

:whistle: :blink: :dry:

Torque makes horsepower

wireman wrote: Torque makes horsepower

Well I learn something everyday. I always though Yoder made horsepowder. :whistle:

wireman wrote: So whats the problem guys?
For once I find myself agreeing with an engineer instead of screaming at one on a jobsite asking where he got his degree! :woohoo: :woohoo: :woohoo: :woohoo: :woohoo:

Well said Del. I can't believe that I'm saying this about myself but its true. As an application engineer I completely agree with Del's assessment and I would like to add that horsepower calculations are the accepted norm in the description of vehicle engine output. Even though the torque is what you feel in the seat of the pants dyno. However, horsepower calculations make more sense in my field of machine tools. Horsepower is an expression of total work done and is critical in the calculation of material removal rates. These calculations are essential when estimating cycle times and determining the proper machine configuration for a given application.

With all that said I find it interesting how horsepower correlates to trap speed in a quarter mile drag race. Again it's an expression of total work done. A given level of horsepower should deliver you to the finish line at a predictable speed pretty much regardless of your reaction time and initial acceleration (60 ft time.) Notice how much can be gained in ET by sorting reaction and initial power delivery but the trap speed doesn't vary much without a horsepower increase.

haha. I often find myself wondering the same thing about other engineers. Don't stop yelling at us though, it's the only way we learn. Remember, engineering degrees are all about math. A couple of the better schools do some hands-on stuff, but there's really no replacement for experience.

I could sit down and design a motorcycle from scratch (it'd take a while of course). But I'm sure whatever I came up with would be completely different from all the standard stuff out there today, just because I'd have taken the problem from a different angle. So I'm still not really a great mechanic, because every time I open something, I have to sit there and look at it and work my way through what the heck everything does, because I haven't seen it before, and it's not how I'd have thought to do it.

that satement was in reply to Wireman, I failed to quote him.

OK Im old back in the day when I went to trade school in Germany architects and engineers had to work at every trade for 3 months and new what the hell they where doing before they graduated after many years. Didnt have a pc

OK Im old back in the day when I went to trade school in Germany architects and engineers had to work at every trade for 3 months and new what the hell they where doing before they graduated after many years. Didnt have a pc

I wish that were still the case. They still try to push internships, but every time companies need to cut budgets, interns are the first to go, so they're hard to come by right now. And all the government regs make it illegal/really hard, to hire interns for free anymore. I had the benefit of going to a small school, so we did almost all of our own machine work on everything, and had an old machinist to scream at us about how dumb we were. But most other engineers I've met in my travels didn't ever set foot in a machine shop. And that's why I've had to call up engineers and explain why I wasn't going to send a drawing out with a square hole. (Mill ends rotate, you can't cut an inside square corner, at least not without some expensive and pointless machinery)