HP vs. Torque

[mrossum]

i have been following a thread elsewhere in this furum about how much hp it takes to spin a pump at a given rpm. my question is this: if i have a panther pump that won't spin a whole lot of rpm anyways, why wouldn't the torque number be more important to me than HP?
at the lower rpm's, the torque is doing the work. at least that is how i was taught when building engines. if you look at the graph of a dyno pull, the torque curve and hp curve intersect at some point. anything to the left of that point represents torque working, and anything to the right represents the hp working. i am by no means an expert, but this is how i was taught.

[steelcomp]

HP and torque are just words to identify a work force. It's the work force that's doing the work, not hp, and not torque. It makes no difference where they cross, because if you call them somehthing else, they may cross in a completely different place...just depends on the converson factor. (look at metric power conversions) Torque is basically a stationary work force...hp is torque which has been converted to relate to time and distance (RPM) using a conversion factor. They're both basically saying the same thing. Because of the conversion factor (and nothinig else) hp and torque cross at 5250rpm. Below that, torque will always be higher than hp, and above, the opposite. That's why it "seems" as if lower rpm is torque related, and high rpm is hp related. It's only a function of math, not the work force being applied.
Hope that helps a little.

[Duane HTP]

Good answer. You stopped this argument dead in it's tracks.

[cfm]

On the subject but off the subject (subject is drag racing - not boats - but may give us some better thought)) - just a quote we should all read and think about. Kinda put a different twist on things:
Darin Morgan writes:
The simple explanation is that raising rpm effectively increases an engine’s displacement. This might seem nonsensical because the volume displaced by the pistons doesn’t change, but consider the effects of filling and emptying the cylinders faster in real time. An internal combustion engine is an air pump, and if we turn that pump faster, we can theoretically burn more fuel in a given amount of time and consequently produce more power. For example, an eight-cylinder engine running at 6,000 rpm fires its cylinders 24,000 times in one minute (assuming perfect combustion). Increase the engine’s speed to 8,000 rpm and it will fire 32,000 times per minute, a 33 percent increase. The volume of air and fuel that moves through the engine is now equivalent to an engine with a much larger displacement. There are also 8,000 additional power pulses per minute transmitted to the crankshaft that can be harnessed to turn the wheels and accelerate the car.
Raising engine speed is analogous to supercharging or turbocharging a motor; the goal is to increase the volume of air and fuel that moves through the engine. The airflow is increased with a forced induction system by pressurizing the intake system; in a naturally aspirated engine, the airflow is increased by raising rpm. If done correctly, both approaches will increase power.
A higher revving engine also permits the use of a numerically higher gear ratio to multiply the engine’s torque all the way down the drag strip. Let’s say an engine that produces 1,000 horsepower at 7,000 rpm is paired with a 4.56:1 rearend gear ratio. If this engine is then modified to produce 1,000 horsepower at 8,000 rpm, it can now pull a 4.88:1 or 5:14:1 rearend gear without running out of rpm before reaching the finish line. The numerically higher gear ratio gives the engine a mechanical advantage by multiplying its torque by a greater number to accelerate the car faster – in effect, it has a longer lever to move the mass.

[steelcomp]

Darrin's a sharp cookie, but his first sentence should read:
The simple explanation is that raising rpm effectively increases an engine’s dynamic displacement. Raising an engine's rpm dosen't change it's static displacement. That's a given. The only time that ever happens is when things start taking on different material properties, and that's never a good thing in an engine. (like when an eight cyl engine becomes a five and a half cyl engine) :cry:
What was the context of this quote? What is the question that this was the "simple" explaintion of? Just curioius.

[Tom Brown]

It's all about torque. Horsepower is just a number the tight t-shirt wearing dyno monkeys like to cite.

[Jbb]

It's all about torque. Horsepower is just a number the tight t-shirt wearing dyno monkeys like to cite.
Testing out the flame retardant touque?.... :p

[mrossum]

all answers above were GREAT answers that shed much needed light on this subject.
back to the original question, though: shoud i be more interested in building a ton of torque at lowqer rpm, or a ton of horsepower at higher rpm???

[steelcomp]

you should be looking to make usable power. Don't focus on irrelevant names. There's a combination of "hp" and "torque" that'll give you what you're looking for. What's the application?

[mrossum]

you should be looking to make usable power. Don't focus on irrelevant names. There's a combination of "hp" and "torque" that'll give you what you're looking for. What's the application?
18 ft Haskell flat bottom with 355 small block chevy and panther pump

[Oldsquirt]

shoud i be more interested in building a ton of torque at lowqer rpm, or a ton of horsepower at higher rpm???
You need to get past this question. Besides, "a ton of torque at lower rpm" really means a ton of HP at lower rpm.
The real question is, "how much power does it takes to turn the pump the necessary rpm to achieve my performance goal". Generally this is about speed. The answer to the question tells you the HP you need and the RPM you need it to be produced at.
18 ft Haskell flat bottom with 355 small block chevy and panther pump
What is the boat currently capable of in terms of speed and rpm?
What are your goals?

[sorry dog]

Darrin's a sharp cookie, but his first sentence should read:
Raising an engine's rpm dosen't change it's static displacement. That's a given. The only time that ever happens is when things start taking on different material properties, and that's never a good thing in an engine. (like when an eight cyl engine becomes a five and a half cyl engine) :cry:
What was the context of this quote? What is the question that this was the "simple" explaintion of? Just curioius.
I don't remember who it was for sure (maybe VW) but they were showing off a variable displacement motor a few years back...but probably too expensive to produce. Aren't the octane testing motors variable??
Anyway... Turbo and Supercharged motors are a bit like variable displacement... Since the range of possible volumetric effeciency at a given RPM is greater compared to a N/A motor...those fancy valve timing motor not withstanding.
...or am I totally full of shit?

[cfm]

Darrin's a sharp cookie, but his first sentence should read:
Raising an engine's rpm dosen't change it's static displacement. That's a given. The only time that ever happens is when things start taking on different material properties, and that's never a good thing in an engine. (like when an eight cyl engine becomes a five and a half cyl engine) :cry:
What was the context of this quote? What is the question that this was the "simple" explaintion of? Just curioius.
That's why I threw this out there - your a thinker and I knew this would mae you sit back for a second. LOL.
The question was relatively simple - "What's faster ?"
So, his answer is very thought producing even though it singles out the very basics of an engine being an 'air pump.'
I took it as this:
For easy math say we have two motors that run flat out for one minute straight. Both are 100% volumetric effecient. Remember, it takes 2 rpm on a 4 stroke for every cylinder to complete their cycles.
Engine #1 is a 454 that turns 7500rpm.
7500/2 x 454cid = 1,702,500 cid per minute
Engine #2 is a 540 that turns 6000rpm
6000/2 x 540cid = 1,620,000 cid per minute
Which displaces more air per minute ?
With both engine's using same A/F ratio, which burns more fuel ?
Which get's more work done per minute ?
==============================
Sorry to get thread off topic a little. I just like opportunities like this to discuss things that make us think, brainstorm, discuss, and throw around a little. Right or wrong - it makes us smarter in the end. Plus, it's just damb fun !!! Lol.

[steelcomp]

Any engine that accelerates a given load from point A to point B faster, wins. Regardless of power.
I've seen engines with more dyno HP get out- accelerated by engines with less comparative power. Why?
Lary Widmer focuses on this in great depth, and it's one of the reasons he's had the success he's had. Numbers just really don't matter. Usable power does. Some people want humbers. Some people want to win.

[poncho-pwr]

One of the oldest sayings in the business, "We don't race dynos!"

[mrossum]

Any engine that accelerates a given load from point A to point B faster, wins. Regardless of power.
I've seen engines with more dyno HP get out- accelerated by engines with less comparative power. Why?
Lary Widmer focuses on this in great depth, and it's one of the reasons he's had the success he's had. Numbers just really don't matter. Usable power does. Some people want humbers. Some people want to win.
i'm not racing, but i will be freshening up my 355 this winter. thought about bumping it up a little. it will go about 3500 rpm now with my panther. would like a little more.................

[poncho-pwr]

If you are gonna stick with the small block I would recommend stroking the motor you have to make it a 383. There are a lot of places like Powerhouse that have some pretty good deals on stroker kits with everything you need for a pretty good price and it doesn't really cost all that much. I don't know what heads you are running but if they aren't a quality piece there are still some good easy to find factory small block heads that work well and are very economical such as the iron vortec heads or even a set of slightly messaged 882s. Making your deal a 383 with some decent iron heads, a good properly selected hydraulic cam, a good intake like an Edelbrock Performer RPM Air-Gap #edl-7501, and a nice carb would probably wake it up nicely and put you where you want to be with that pump.
What heads are on your motor and what are it's internals?

[bruleracer]

Just a thought,,, I know you guys are talking engines here,But,,what if you think this thing from the other END.. I'll call it impellor limted,,, does the
boat with a AA and a 540 @ 6000rpm go as quick as a boat with a FF impellor and a 283 cid @1200rpm ???

[steelcomp]

Just a thought,,, I know you guys are talking engines here,But,,what if you think this thing from the other END.. I'll call it impellor limted,,, does the
boat with a AA and a 540 @ 6000rpm go as quick as a boat with a FF impellor and a 283 cid @1200rpm ???Isn't that the $64 question with jet pump impellers? At what rpm do they cross? What I mean is, at what respective r'spm are an A, B, and c flowing the same GPM?
BTW...Impeller couldn't care what motor's behind it. Impeller only cares about RPM, and power consumed. Could be a rat on a treadmill. :rollside: From what I've learned, though, the bigger impeller is going to be quicker with better holeshot.

[bruleracer]

Geeeeze,,, What up Steele, just wanted to see whos up. been a while.
I'd call all this the 124 million doller Q. Thats why where here!! hows it
going. Good look on the boat!!!

[bp]

Just a thought,,, I know you guys are talking engines here,But,,what if you think this thing from the other END.. I'll call it impellor limted,,, does the
boat with a AA and a 540 @ 6000rpm go as quick as a boat with a FF impellor and a 283 cid @1200rpm ???
hi steve. that's easy; the boat with the aa/540 at 6k, rather than a pocket engine revving to 12k, if they're the same hulls with the same weight :) i thought we settled this a long time ago? :cool:
you have the size and mass in your arm and body to lift that 100lb dumbell, but how many times can you curl it in a minute?
a pump requires power to perform work (work being the curls). if you don't have enough power, you're only going to curl that 100lbs 1 or 2 times in a minute. if you have lots of power, you can curl it 20-30 times in a minute. if you reduce the amount of weight, you might be able to curl it more times in a minute, but did you really do the same amount of work? (you'd have to curl 50lbs 40-60 times to be equal).
the larger impeller is more efficient because, for one thing, it can pump more water (more work/thrust) with fewer revolutions. the ff will struggle to provide the same type/amount of work, even with the same hp applied (at a much higher rpm).
to get more work/thrust out of the larger (a or b) impeller, you need more power.

[steelcomp]

Geeeeze,,, What up Steele, just wanted to see whos up. been a while.
I'd call all this the 124 million doller Q. Thats why where here!! hows it
going. Good look on the boat!!!What up Brule'. Guess I missed this lastnight. Been a year...almost exactly. Thanks for the good luck. Should be interesting.
Hope to see ya.

[gforceauto]

Ok!!!!! I Am Going Threw The Same Problem. I Put 8000.00 And Stroked My Sbc And Still 3500, Went To A Ab Cut Impeller Also. I Am Doing A Cam Change At The Moment Ill Get Back With You To See If This Solved My Problem.
T

[SB]

If you are gonna stick with the small block I would recommend stroking the motor you have to make it a 383. There are a lot of places like Powerhouse that have some pretty good deals on stroker kits with everything you need for a pretty good price and it doesn't really cost all that much. I don't know what heads you are running but if they aren't a quality piece there are still some good easy to find factory small block heads that work well and are very economical such as the iron vortec heads or even a set of slightly messaged 882s. Making your deal a 383 with some decent iron heads, a good properly selected hydraulic cam, a good intake like an Edelbrock Performer RPM Air-Gap #edl-7501, and a nice carb would probably wake it up nicely and put you where you want to be with that pump.
What heads are on your motor and what are it's internals?
Agreed.
Taking another angle on this answer: Stroking the motor gives you more cubic inches and more torque (more horsepower at a lower rpm) where you need it.
It does a jet little good to develop hp at 8,000 rpm.

[Tom Brown]

I've seen engines with more dyno HP get out- accelerated by engines with less comparative power. Why?
Gearing. Setup efficiency. Weight.
If the hp numbers are normalized so it's apples to apples and the work being done is the same, more horsepower always wins... by definition.
One thing about tight t-shirts is the sleeves give me a place to keep my smokes. :cool:

[Tom Brown]

hi steve. that's easy; the boat with the aa/540 at 6k, rather than a pocket engine revving to 12k, if they're the same hulls with the same weight :) i thought we settled this a long time ago? :cool:
If it was settled in favor of the larger displacement engine, then it was settled wrong.
There is no advantage to a slower turning, larger displacement engine, as compared to a faster turning, lower displacement engine. If there are performance differences at the same power levels, then something else in the setup is different causing the performance deviation.

[PC Rat]

It does a jet little good to develop hp at 8,000 rpm.
It does if you're turning the jet 8,000 rpm as well.

[PC Rat]

Ok!!!!! I Am Going Threw The Same Problem. I Put 8000.00 And Stroked My Sbc And Still 3500, Went To A Ab Cut Impeller Also. I Am Doing A Cam Change At The Moment Ill Get Back With You To See If This Solved My Problem.
T
The Berkeley chart I have doesn't even go that low. Must be in the neighborhood of 130hp to spin a stock pump with an AB to 3500 rpm.

[SmokinLowriderSS]

Good guess. :)
According to JPCalc, 126.5 is an AB @ 3500RPM.

[steelcomp]

If it was settled in favor of the larger displacement engine, then it was settled wrong.
There is no advantage to a slower turning, larger displacement engine, as compared to a faster turning, lower displacement engine. If there are performance differences at the same power levels, then something else in the setup is different causing the performance deviation.
There are HUGE advantages to a slower turning, bigger motor, but that's not the whole picture. You're not ocnsidering impeller efficiency. Bigger impeller turning slower will stay more within it's efficiency range than a smaller impeller turning faster. As impellers get smaller, so does theier window of efficiency, ultimately to a point of no return. It may be favorable to turn an engine to 7500 to make the good power, but not necessarily the impeller. It's always favorable to build power at the lowest RPM you can, and still make the power you need. High RPM = broken parts = DNF = you lose.

[steelcomp]

QUOTE=Tom Brown]Gearing. Setup efficiency. Weight.
If the hp numbers are normalized so it's apples to apples and the work being done is the same, more horsepower always wins... by definition.
One thing about tight t-shirts is the sleeves give me a place to keep my smokes. :cool:[/QUOTE]The example I was referring to was on the dyno...no gearing, no weight, no set-up.
What do you mean by "If the hp numbers are normalized so it's apples to apples"?? Of course if everything is identical, then the more hp will win. If grandma had balls, she'd be grandpa.
I'm talking about an engine with 675 hp being out accelerated by an engine with 650 hp. I'm trying to illustratr how irrelevant hp numbers are as numbers, and that what's important is usable power. It's not really applicable in jets, since jets don't really ahve to accelerate through a power band. They just basically go to an rpm and stay there. In most other forms of racing, though, an engine is required to pull through an rpm range, and the more usable power you have throughout that needed rpm range, the faster the engine's going to accelerate, regardless of peak hp. That 675 hp motor may peak at 7800, but from 5500-7500 may be a dog. Keep it within 200-300 rpm of that peak power range, and you'll be all right, but miss a shift, come out of a cornner too slow, or gear your set-up wrong, and you'll think that motor's a dog. In the mean time, the guy with the 650 hp motor that built his motor with usable power in mind, instead of peak "numbers" is cutting lap times that you only wish you could. He can use his power at 6000, 6500, 7000, and so on. Maybe his peak numbers aren't as good, but he has much more usable power. On a dyno, that 650 hp motor will out accelerate that 675 hp motor, even though the 675 hp motor makes more power.
This example is using two basically equal motors (rule limited SBC's) with two different mindsets in their design. Also, since the engine with more usable power can work over a wider rpm range, it's a lot easier on parts and is going to finish more races, and be easier on the racer's engine budget.

[Tom Brown]

...On a dyno, that 650 hp motor will out accelerate that 675 hp motor, even though the 675 hp motor makes more power.
In this example, the 675 hp motor doesn't make more power. It makes less power than the 650 hp engine because the 650 hp engine is out accellerating it, therefore, it has more power.
The 675 hp engine makes more peak power but not generally more power if it is being out accellerated.

[steelcomp]

In this example, the 675 hp motor doesn't make more power. It makes less power than the 650 hp engine because the 650 hp engine is out accellerating it, therefore, it has more power.
The 675 hp engine makes more peak power but not generally more power if it is being out accellerated.Exactly my point...more power (usable), not horsepower. It's amazing at what levels of pro racing there are guys who don't get this.

[Tom Brown]

Exactly my point...more power (usable), not horsepower.
I'm not with you there.
The 650 hp engine has more total horsepower in the needed band than the 675 hp engine that is being out accellerated. The 650 hp engine has more area under the relevant part of the horsepower graph than the 675 hp engine, despite the 675 hp engine having a higher peak. Both concepts are horsepower related but one is peak and one is average within a band.

[Tom Brown]

OK... how about this for a scenario.
Let's say we have a boat engine that can kick out 400 hp at 5000 RPM with a redline of 5000 RPM. This boat runs a 30p prop and can do 63 mph @ 5000 RPM (I threw in 2:1 gears with 11% slip, 5000 lb boat)
OK. Let's modify the engine...
We put on some 4 valve heads, a big fat cam package, heavy valve springs, big open exhaust system, and the whole thing is balanced to a high degree. Now we're creating 500 hp at 7000 RPM (our new redline thanks to the balancing) but the high flowing engine has lost 20% of it's power at low RPM.
On the top end, with the new power, we can now do 70 mph (I used power:weight and efficiency calculations to come up with a pseudo-real numbers here). That's good, but how much did we lose on the low end?
Well, to get to 70 mph, we had to revv the engine higher to get it to peak power. Now we're running a 24p prop @ 7000 RPM (same 2:1 gears, 5000 lb boat, and I'll assume the same 11% slip... although the slip will probably go down a little bit as the speed increases and, therefore, drag decreases).
There will be no change in low end power, despite the 20% reduction in crankshaft power, because the 24p prop has 20% less pitch than the 30p prop, giving it a 20% mechanical advantage over the 30p prop so low end performance stays the same but with more top speed.
That's why, if you compare a tiny screamer to a slow turning big displacement engine, they can be exactly the same. If the tiny engine has half the low end torque but can rev twice as high with the same horsepower, you simply run 2:1 gearing (with reference to the big engine) and have exactly the same power output at all ranges.

[steelcomp]

I'm not with you there.
The 650 hp engine has more total horsepower in the needed band than the 675 hp engine that is being out accellerated. The 650 hp engine has more area under the relevant part of the horsepower graph than the 675 hp engine, despite the 675 hp engine having a higher peak. Both concepts are horsepower related but one is peak and one is average within a band.Horsepower under the curve may be more, may not be. At then end of the curve, the bigger power may very well be accelerating faster, but the wider power is already there and gone.
You're not going to get what I'm trying to explain by focusing on HP. HP in itself does not represent performance. Acceleration does.
Try this.
What makes an engine accelerate? Hint...it isn't HP.

[Tom Brown]

Try this.
What makes an engine accelerate?
Horsepower. :cool: