Horse 1, Jess 0

[GAAN]

i've never understood HP. I get the idea of torque but HP is voodoo. how can a diesel motor make 1500 lbs/ft of torque and a gas motor make 350 lbs/ft of torque and both make 500 HP?

[somegirl]

The real problem on the horse is the suspension.

[Speeddog]

i've never understood HP. I get the idea of torque but HP is voodoo. how can a diesel motor make 1500 lbs/ft of torque and a gas motor make 350 lbs/ft of torque and both make 500 HP?

Diesel motors are generally low rpm, compared to gasoline motors of the same size.
Principally due to using really high compression ratios, and the cylinder pressure at ignition is pretty severe.
Parts are beefy and heavy, so that's a hindrance to running at high rpm.

I haven't seen any of the power/torque info on latest racing diesels, or even hot production automotive stuff, that'd be some interesting numbers.

[x136]

i've never understood HP. I get the idea of torque but HP is voodoo. how can a diesel motor make 1500 lbs/ft of torque and a gas motor make 350 lbs/ft of torque and both make 500 HP?

"Horsepower is a function of torque," was how I'd heard it said, but that didn't make sense to me, either. Wikipedia's articles on torque and horsepower have waaay too much information, but this article at The Straight Dope is much more helpful and Englishy, even with the graphs and equations missing.

Basically, given the torque (in lb-ft) and RPM of an engine, you can find the horsepower produced.

Torque x RPM
----------------   =   HP
       5252

[Ash]

torque is force times distance

horsepower is, uh, power

power is force applied in a distance over time

so engines that spin faster at the same torque output (force * distance) are producing more power because the torque is being applied more often.

layman's terms...

[GAAN]

seems like that would be more power applied to make torque

[Ash]

torque makes the power, not the other way around

power is just torque integrated over time

[bigiain]

seems like that would be more power applied to make torque

Torque is just how hard it can push - the fact that it's rotating complicates the understanding, ignore that for a minute and treat "torque" as "force". You can push your bike (or a wheelbarrow or a horse) with 1lb of force and it'll barely move, or you can push it with 200lbs of force and it'll start accelerating - the less weight and friction the faster it'll accelerate.

Now think about what happens as the bike speeds up - when it's doing walking pace, you can probably still apply 200lbs of force. when it gets to a jog, or a fast jog, you'll be unable to push it that hard anymore - the amount of force you're applying drops as the speed increases. By the time you hit running speed, the amount of force you can apply drops even further, and at a fast run you won't be able to apply any force to the bike at all.

"Power" is a measure of how much force you can apply at a particular speed. Anybody with enough strength can push against a wall at 200lbs, but without anything moving, no "work" is being done, and no "power" is being used. If you can push 200lbs at 1 foot per second, thats 200 foot pounds per second. If you get to 20 feet per second and were still able to push at 200lbs, that'd be 40,000 foot pounds per second. But you wont, because 20 feet per second is ~13mph which is a pretty fast run (it's _almost_ a 4 minute mile) - if you can even get that fast, you won't have anything "left over" to push the bike with. 40,000 foot pounds per second, as it turns out, is about what a 900 monster can do. By convention, people decided to call 550 foot pounds per second "1 horsepower", so 40,000 foot pounds is ~72hp. That same ~72hp Monster can only provide 100lbs of "push force" at 400 feet per second(26mph) or 50 lbs of force at 800 feet per second (52mph). (and as the speed goes up, you need to share the available "force" between overcoming air resistance and making the bike go faster - thats why you can't keep going and say "at 1600fps it can push 25lbs and at 3200fps it can push 12.5lbs", cause 12.5lbs isn't enough force to overcome air resistance as 216mph - unless you're on Randalls 620, anyway...) That also shows why the gear you're in doesn't matter - in 1st gear the engine provides a lot of force, but it'll only get up to 40 or 50mph or so before running out of puff. In top gear it'll go around 3 times faster than that, but with only 1/3rd of the force - which is why it accelerates so much slower in 6th - half the force at twice the speed is exactly the same "power" as twice the force at half the speed or 1/3rd the force at 3 times the speed.

Getting back to torque from force: Torque can be translated directly into tractive force by multiplying the gear ratios (primary drive ~2:1, gear ratios of say 3:1 in 1st down to ~1:1 in 6th, and final drive at ~3:1) and then dividing by the wheel radius, so the ~55 foot pounds of torque a 2 valve 900 makes turns into 990 foot pounds at the wheel (55*2*3*3) which with a rear wheel radius of really close to 1 foot means peak torque provides ~990lbs of force in 1st gear, or 1/3rd of that in top gear. That happens at ~6750rpm, which is 375rpm at the wheel in 1st (6750/2/3/3) or 1125rpm in 6th. So 990lbs of force at 375rpm on a 1 foot diameter wheel is 2*pi*1foot * 375rpm =~ 2355 feet per minute or 39 feet per second (2355/60).That gives us ~39000 foot pounds per second (39*990) -  In top gear we'd get 330lbs of force at 1125rpm, which is _also_ ~39000 foot pounds per second (we just divided the force by 3 and multipled the speed by 3 to get the same number). 39000, divided by that "550 foot pounds per second = 1 hp" I told you about above, gives us ~71hp - woot, my numbers all make sense!

Hmmm, I've spent way too long on this post - hope it helps _somebodies_ understanding...

big

[GAAN]

holy shit big...looky J's bruise...pretty colors

[Ash]

ADD


and i cant sleep

frack

[GAAN]

play with your carrot, that usually helps me

[NAKID]

holy shit big...looky J's bruise...pretty colors

Post up pics!

[Slide Panda]

This thread is useless w/o pix 

[swampduc]

The real problem on the horse is the suspension.

If you look at JBub's incident, the primary problem is one of controls - the throttle and brakes lack feel and accuracy, while the fueling is far from smooth.

And +1 on pics 

[Slide Panda]

If you look at JBub's incident, the primary problem is one of controls - the throttle and brakes lack feel and accuracy, while the fueling is far from smooth.

And +1 on pics 

I also hear they have terrible emissions problems from that fueling.  Don't stand behind one when the start up.