HP vs. Torque
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From: Cummins Technical Center, IN
Originally Posted by 1sttruck
"Regardless, though-- the number of gears required in the gearbox is a function of the RPM range where the engine makes useable power. The mining truck only makes useable power from say 800- 1500 rpm. That's a powerband of 700rpm.
The NASCAR would make useful power from 6000 to 8000 rpm, and require FEWER gears."
Which is my point, are you going to rev the nascar engine to 7 grand and pop or slip the the clutch ? Where low torque gas engines are used in place of higher torque diesels one sees either the same number of gears but a lower top speed due to the gearing, or the same top speed but more gears to get it there. Torque is handy when it comes to moving large loads, as even though the peak hp for the high torque engine may be lower than a high hp low torque enhine, the hp at the lower rpm off of idle is typically higher.
The NASCAR would make useful power from 6000 to 8000 rpm, and require FEWER gears."
Which is my point, are you going to rev the nascar engine to 7 grand and pop or slip the the clutch ? Where low torque gas engines are used in place of higher torque diesels one sees either the same number of gears but a lower top speed due to the gearing, or the same top speed but more gears to get it there. Torque is handy when it comes to moving large loads, as even though the peak hp for the high torque engine may be lower than a high hp low torque enhine, the hp at the lower rpm off of idle is typically higher.
If a gas engine is tuned for a narrow RPM band (usually LOW rpm as well), then it will often have the same number of gears as a diesel because of the narrow RPM band.
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yeah, torque is great... but these trucks have plenty!!! so, as I said before, all I care about is horsepower... with these trucks... weren't we talking about Cummins 5.9 engines?
I'm hoping my 98 will make full boost by 1600rpm and I'll probably shift it at 4000rpm... not a horrible power band IMHO.
I'm hoping for at least 600rwhp... how much torque will it make? don't care... it'll be more than I want or need...
I'm hoping my 98 will make full boost by 1600rpm and I'll probably shift it at 4000rpm... not a horrible power band IMHO.
I'm hoping for at least 600rwhp... how much torque will it make? don't care... it'll be more than I want or need...
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From: Cypress, TX
Originally Posted by HOHN
Rusty's explanation of HP using the example of "high torque" horse and "high rpm" horse is brilliant. It perfectly explains the concept of power vs tq.
The problem comes when we try to relate this to ACCELERATION, which is a typical measurement of "performance".
The problem comes when we try to relate this to ACCELERATION, which is a typical measurement of "performance".
You're right - the classical definitions are steady state in that they ignore the effects of inertia. They are much more valid, however, when one's measure of "performance" is getting a 16,000 lb GVWR 5th wheel to the top of a 6% grade. In that sense, "lifting" a load to the top of a hill at what one would like to be a constant velocity is very much like lifting water out of a mine shaft.
Rusty
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From: Cummins Technical Center, IN
I agree.
The key difference being the ability to SUSTAIN a given rate of work (power), versus being able change the rate of work accomplishment (dynamic).
If steady state we all we wanted, then a massive flywheel might be a GOOD thing, actually, because what you lose in acceleration you'd gain somewhat in the ability to climb hills.
Unfortunately, you'd have to have an unreasonably heavy fwl to realize any noticeable benefit in climbing, and the penalty to acceleration would be disproportionately large.
I'm impressed that you and Forrest actually read my long-winded missive!
The key difference being the ability to SUSTAIN a given rate of work (power), versus being able change the rate of work accomplishment (dynamic).
If steady state we all we wanted, then a massive flywheel might be a GOOD thing, actually, because what you lose in acceleration you'd gain somewhat in the ability to climb hills.
Unfortunately, you'd have to have an unreasonably heavy fwl to realize any noticeable benefit in climbing, and the penalty to acceleration would be disproportionately large.
I'm impressed that you and Forrest actually read my long-winded missive!
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From: Alberta Canada
Brake Power = torque X radians
Killowatts = Newton meters X Radians
Sorry to the Fellas from the the US, but yes this is in metric.
Simply put, Power is that Rate at which Torque is delivered. That's why when you make 700 lb/ft (931 newton meters) at 1400 rpm (146.61 radians) versus 700 lb/ft (931 newton meters) at 2800 rpm (293.22 radians) the engine output doubles from 182.898 HP (136,492watts/136.49 kw) to 365.8 HP (272,984 watts/272.98Kw). The third factor in the English (American) formula is to compensate for the English units (HP, lbs/ft) and the fact that even up here in Canada we look at Revolutions Per Minute and not Radians Per Second (rpm divided 60 X by 2 X by PI (3.1415)). In other words, Torque X RPM divided by an easily remembered factor gives you Horse Power. An engineer, a metric one that is, would calulate it into kilowatts and then convert to HP by multiplying it by 1.34 (ie 1 kw equals 1.34 hp) (as well 1lb/ft equals 1.34 newton/meters) To tick off some of the Chevy Ford gas scrappers where I worked, I would explain this and then make the statement that Power Output, be it Horse Power or Watts is simply a calculation and therefore dosn't really exist. Sorry fellas. More torque means more output, if you can't make more torque with out it breaking, spin it faster, and if you can't do that, then you are done when it comes to trying to CALCULATE the OUTPUT of your unit. Do you want to hear my
on the IP=PLAN formula?
Killowatts = Newton meters X Radians
Sorry to the Fellas from the the US, but yes this is in metric.
Simply put, Power is that Rate at which Torque is delivered. That's why when you make 700 lb/ft (931 newton meters) at 1400 rpm (146.61 radians) versus 700 lb/ft (931 newton meters) at 2800 rpm (293.22 radians) the engine output doubles from 182.898 HP (136,492watts/136.49 kw) to 365.8 HP (272,984 watts/272.98Kw). The third factor in the English (American) formula is to compensate for the English units (HP, lbs/ft) and the fact that even up here in Canada we look at Revolutions Per Minute and not Radians Per Second (rpm divided 60 X by 2 X by PI (3.1415)). In other words, Torque X RPM divided by an easily remembered factor gives you Horse Power. An engineer, a metric one that is, would calulate it into kilowatts and then convert to HP by multiplying it by 1.34 (ie 1 kw equals 1.34 hp) (as well 1lb/ft equals 1.34 newton/meters) To tick off some of the Chevy Ford gas scrappers where I worked, I would explain this and then make the statement that Power Output, be it Horse Power or Watts is simply a calculation and therefore dosn't really exist. Sorry fellas. More torque means more output, if you can't make more torque with out it breaking, spin it faster, and if you can't do that, then you are done when it comes to trying to CALCULATE the OUTPUT of your unit. Do you want to hear my
on the IP=PLAN formula?
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From: Cypress, TX
Originally Posted by qmcdt
Do you want to hear my on the IP=PLAN formula?
on the IP=PLAN formula?Where:
P = mean effective pressure, in PSI
L = length of stroke, in feet
A = area of piston, in square inches
N = number of power strokes per minute
Rusty
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From: Alberta Canada
you got her. that divided by 33000 is the metric to english conversion. in the original version
indicated power=mean pressure in megapascels X length of stroke in meters X area of cylinder in meters squared X number of power stokes per second
I hope no one thinks I'm talkin down to anyone here, it's just that I've seen guy's almost come to fistacuffs over something that doesn't even exist until a couple or three of numbers are smashed together with an adding machine. Knowledge is the only true POWER.
indicated power=mean pressure in megapascels X length of stroke in meters X area of cylinder in meters squared X number of power stokes per second
I hope no one thinks I'm talkin down to anyone here, it's just that I've seen guy's almost come to fistacuffs over something that doesn't even exist until a couple or three of numbers are smashed together with an adding machine. Knowledge is the only true POWER.
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From: Cypress, TX
Originally Posted by qmcdt
you got her. that divided by 33000 is the metric to english conversion. in the original version.
The equation yields BHP if one uses brake mean effective pressure and IHP if one uses indicated mean effective pressure. Both mean effective pressures are theoretical (calculated) values, anyway.
The significance of this equation (linear frame of reference) is that HP = (Torque x RPM) / 5252 is derived from it and translates it to a rotational frame of reference.
Rusty
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