Page 5 of 12 FirstFirst 123456789 ... LastLast
Results 41 to 50 of 111

Thread: Torque or HP?

  1. #41
    LVjetboy
    "Why? Because the torque drops off so quickly compared to the horsepower gain."
    Kojac, first let me say I appreciate your thoughts and ideas on this topic. The more we think about this and the physics of what's happening the better. That said, your conclusion is wrong. How fast torque "drops off" compared to power gain has nothing to do with performance. Some have suggested an equation relating the ideal distance between peak torque and peak power for impeller matching. Also BS. Some have also suggested the rpm where torque and power cross is ideal...trying in vain to keep torque a perfomance player, only to discover that units (metric or english or whatever) drive the rpm crossing point not performance.
    The only driver of performance is total power delivered to the impeller and the pump/impeller efficiency at that rpm.
    Period.
    Efficiency does make a difference but is related to power not torque. Efficiency is defined as power out over power in. Not torque out over torque in and for a good reason! FOR A GOOD REASON > Think about that. Performance is always related to power and efficency not torque no matter a jet boat, airplane, car or steam turbine.
    The reason a small impeller matched to peak power on a high rpm engine doesn't perform is because that smaller impeller wastes power from flow losses. Less efficient. A less efficient impeller will burn more power to convert to the same thrust. And jet thrust equals performance. Not torque. Has nothing to do with the magnitude of torque applied or how fast the torque curve falls compared to the power curve. Only how much power applied and how effective the impeller/pump converts that power to thrust.
    Those who insist on relating performance to torque are missing the truth and following a torque myth. Trying in vain to bend physics to a preconceived notion of how torque and how the torque curve behaves must in some way equal performance.
    jer

  2. #42
    CrdStang
    I think everyone needs to be reminded that:
    Torque x RPM / 5252 = Horse Power
    At a given RPM, HP cannot increase without torque increase since HP is just a figure of torque x RPM. It's not possible for engine A to make more HP than engine B (at the same RPM) if it produces less torque.
    It's a calculated figure. Think about it like this,
    How much weight you can lift
    x
    how fast you can lift it
    / 5252
    (mathmatical constant)
    = how much power you are really developing.

  3. #43
    LVjetboy
    "I think everyone needs to be reminded that: Torque x RPM / 5252 = Horse Power"
    Not sure everyone needs reminding? That equation's been posted time and time again. Most here've seen it. But that equation seems not to disuade those who champion torque as a measure of performance. Yes, torque and power are related by that equation (English units) and yes, more torque means more power.
    But no, torque and power are not the same thing. And no, just because at a given rpm more torque means more power does not mean an engine designed to produce peak torque at a lower rpm will preform better than an engine producing peak power at a higher rpm.
    Or that once the engine design is set, matching an impeller to peak torque will give the same result as matching the impeller to peak power.
    jer

  4. #44
    steelcomp
    So Jer, (being completely sincere, here...no bs) what is the difference between q and hp??

  5. #45
    Cas
    Yes, torque and power are related by that equation (English units) and yes, more torque means more power.
    Exactly!
    But no, torque and power are not the same thing. And no, just because at a given rpm more torque means more power does not mean an engine designed to produce peak torque at a lower rpm will preform better than an engine producing peak power at a higher rpm.
    Jer, Jer, Jer, tq at low rpms will do very little with a jet. The tq needs to be higher up in the rpm curve. As we talked about before, there's no way your engine would move you along the way it does if your peak tq was at 3K. Your engine also wouldn't move you along the way it does if it only had 300 ft lbs of tq.
    Ya gotta have the tq in the right rpm range.
    Or that once the engine design is set, matching an impeller to peak torque will give the same result as matching the impeller to peak power.
    most definitely
    so, how've you been?

  6. #46
    kojac
    "Why? Because the torque drops off so quickly compared to the horsepower gain."
    Kojac, first let me say I appreciate your thoughts and ideas on this topic. The more we think about this and the physics of what's happening the better. That said, your conclusion is wrong. How fast torque "drops off" compared to power gain has nothing to do with performance. Some have suggested an equation relating the ideal distance between peak torque and peak power for impeller matching. Also BS. Some have also suggested the rpm where torque and power cross is ideal...trying in vain to keep torque a perfomance player, only to discover that units (metric or english or whatever) drive the rpm crossing point not performance.
    The only driver of performance is total power delivered to the impeller and the pump/impeller efficiency at that rpm.
    Period.
    Efficiency does make a difference but is related to power not torque. Efficiency is defined as power out over power in. Not torque out over torque in and for a good reason! FOR A GOOD REASON > Think about that. Performance is always related to power and efficency not torque no matter a jet boat, airplane, car or steam turbine.
    The reason a small impeller matched to peak power on a high rpm engine doesn't perform is because that smaller impeller wastes power from flow losses. Less efficient. A less efficient impeller will burn more power to convert to the same thrust. And jet thrust equals performance. Not torque. Has nothing to do with the magnitude of torque applied or how fast the torque curve falls compared to the power curve. Only how much power applied and how effective the impeller/pump converts that power to thrust.
    Those who insist on relating performance to torque are missing the truth and following a torque myth. Trying in vain to bend physics to a preconceived notion of how torque and how the torque curve behaves must in some way equal performance.
    jer
    Jer,
    Please,Just show me.
    I have seen a small block on the dyno that make 720 hp at 8200rpm's. Put it in a jet boat with an a/b impellar and it wouldn't pull more than 5600 rpm's. Why? Not enough torque past 5600 compared with the hp to turn it.
    I had a buddy that had a 468 chevy 13.1 compression two carbs big roller turning a don bowers pump 6100 rpm's at the races in a well setup placecraft. doing 108 through the quarter. He built a similiar set up with a 588 cu inch and turned the same rpm's and same speed. The big motor made much more horse power than the 468 (over 250 as I recall)and over 195 more ft pounds of total torque.
    But looking at the dyno sheets they both had the same torque/ horsepower pattern where the torque fell off as the horsepower rose at almost exactly the same rpm.
    He just couldn't understand it.He cried like a baby. All that money spent to accomplish the same thing.
    Then he had his cam profile changed to a longer duration, Shortened his intake and exhaust lengths and reduced the size of his ports in the heads and intake to create more velocity, along with a different port change in his heads to create a torque profile not to fall off until 6300rpm's. Even then it did not drop faster than horsepower rose.
    Motor pulled 7200 rpm's to go 128mph in the quarter at Augusta Georgia with temperature above 98 degrees.
    I would love to see Diggler's motor pull 6500 rpm's with an a/b impellar as I'm sure he would. I could get rid of my blower on one of the motors and drop the compression on my other motors remove fortyeleven carbs have less complicated motors, less maintanance,less work, more time for boating, use less gas and love life.
    Just show me how. Pleeassssssse.
    Kojac

  7. #47
    Floored
    HP is a time vs distance equation. tq is a rotational force or leverage. the impeller in water has a certain resistance value by nature of its size or cut. the engine can only overcome this resistance to the point where input rotation force and resistance to rotation equal out. How to make it rotate faster? Either reduce the resistance value of the impeller(cut it or change blade angles) or add more leverage (TQ). The crazy thing is when you add more tq the hp also rises, being a mathamatical equation and all. The key would be a very flat tq curve at the rpm range to work with your impeller. dne motors come to mind, eh Jer. :coffeycup

  8. #48
    Cas
    Koj,
    I'm sure Jer is just going to say the engine wasn't matched to the pump/impeller.....put a C in it and it'll turn more R's. But would just turning more R's be very efficient?

  9. #49
    victorfb
    what alot of people fail to remember is the fact that LOAD is also applied to this equation. the arguements will continue to go back and forth but the examples are a proving factor. yes i am a believer that torque curves that stay at a higher rpm level is the key to performance on a jet boat. not only is the load increased to the pump with higher rpm, but also the load of having to propell the boat through friction of water and solid. i dont blame some people for sticking to thier guns about thinking HP is the only measure of power, but for those that say it let me ask you this. if i remove the 270 hp 454 from my duelly, and install nissans 320 hp V6, will i be able to pull the 5th wheel with 14000 pounds easier? if HP is a true measure of power, than it should pull much harder with the added 50 HP. HP is HP isnt it? i think id lay money on the 454 pulling harder. the mathimatical equation posted is and will allways be the only way to measure HP but what many seem to forget is the fact that if you change the equation and not have the 5252 meeting point you will not get the corrected HP. also remember that load is a constant on a boat. not only the increase in preasure inside the pump, but also the hull and water friction. bigger boats obviosly increase hull load. try moving a 22' cruiser with a high HP low torque motor. its not going to happen. the saying "no replacement for dissplacement"? why do you think this holds true? larger dissplacement equalls more torque possabilities. a turbo charged mazda rotary can achieve 400 HP but they lack the torque for any heavy loads. you think that rotary will push a 19' jet boat easier and faster than a 300HP big block? NOPE....

  10. #50
    steelcomp
    I think I mis stated my question for Jer. Let me try again. If what you're calling peak power isn't based on the relationship or ratio between q and hp, then what is it that you are calling peak power? You keep saying power- power- power. What is power? Where is peak power achieved, and if we don't use q as a factor, then what do we use?
    Those who insist on relating performance to torque are missing the truth and following a torque myth. Trying in vain to bend physics to a preconceived notion of how torque and how the torque curve behaves must in some way equal performance.
    Of course how the torque curve behaves is important. How can it not be??
    Torque is only a word, but it is the definative word to describe where peak power is being achieved. Torque is the measure of the work the motor is doing, or at least it's the word that we americans have chosen to describe it.
    If it's not, then PLEASE, stop telling everyone that they're wrong, and tell us how you measure where peak "power" is. What is "peak power"? How do we measure "peak power" without having something to describe the work the motor is doing? :coffeycup
    Here's an interesting analogy, since we Americans use horse power.
    Two horses.
    A Thoroughbred and a Klidesdale.
    Tie them both to a lever arm, or an equal cart of coal, if you will.
    The Klidesdale pulls the cart of coal a hundred feet in 30 secs without breaking a sweat, or say pulls 1000 lbs on the lever arm. (Torque)
    The Thoroughbred can hardly pull the cart of coal and struggles to pull it a hundred feet at all, and pulls say 500 lbs on the lever.
    Now cut them loose.
    What happens?
    The Klidesdale can't run much faster than it pulled tha cart, but the Thoroughbred sprints off like the wind, and will run for miles like that.
    Which has more power?

Page 5 of 12 FirstFirst 123456789 ... LastLast

Similar Threads

  1. HP or TORQUE
    By mikey-jones in forum Jet Boats
    Replies: 65
    Last Post: 01-10-2009, 12:20 PM
  2. HP vs. Torque
    By mrossum in forum Jet Boats
    Replies: 36
    Last Post: 09-14-2006, 09:52 PM
  3. Torque? we dont need no stinking torque....
    By Blown 472 in forum Gear Heads
    Replies: 6
    Last Post: 10-30-2004, 06:03 PM
  4. Torque or HP????
    By Norseman in forum Gear Heads
    Replies: 5
    Last Post: 08-14-2004, 12:19 AM
  5. Torque spec, B&M 250???
    By Craig in forum Gear Heads
    Replies: 6
    Last Post: 08-06-2002, 03:34 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •