Torque or HP?

[steelcomp]

doesn't it depend on the size of the wagon wheels?
Alfalfa or oats, is what I was told. :hammer2:

[LVjetboy]

"in all the specs for the different engines I've see here, everyone talks about the HP ratings on their engines with no mention of torque."
That's because it's all about power to the pump. And how well that power is converted to thrust (impeller efficiency). Torque is for wrenches. Those who claim torque and power are the same don't really understand the difference between the two. They are not the same.
There are racers who've applied max torque to the impeller (with cut size) hoping for best performance. There are racers who've applied max power to the impeller hoping for best performance. You think they got the same result?
No. Why?
Because torque and power are not the same thing. And yes, understanding the difference can be important. You'll read a lot of myths about how torque is more basic and "what a dyno measures" so it must be key? In the end, just myths....often repeated by well-intentioned and sometimes well-respected sources until accepted as fact.
Think about it. What does a dyno really measure?
True, at any given rpm, more torque means more power. But also true...an engine can be built for more low end torque (power) or more high end power. And once built, an impeller can be matched to peak torque or peak power. Those two match points will not give the same performance. So even though Q and Hp are related, how well you understand the physics can make a difference in your jets performance. Power to the impeller is what it's all about. And how efficiently that power is converted to thrust (a factor of cut size among other things) Torque is only half the equation.
jer

[Performance 19]

That's exactly what I was being sarcastic about. It cracks me up to hear the question "Does it take torque or horsepower?" with no concern as to what rpm range the engine makes power.
I'll take a torque motor, just give it to me at 6,000 rpm.
Brian
Yep, that pretty much says it all for me too.

[CrdStang]

Oh hell, I'll throw in my two cents:
Given that a jet takes more horse power to spin faster, the more power you have, the faster you go. It's not a car, it doesn't need a fat "torque curve". Average torque over the RPM range means absolutely jack to a jet. It's about HORSE POWER.
So what does this mean? Figure out the maxium RPM you want to run your engine at for extended periods of time. Choose parts (cam, intake, ect) that make the most power at that RPM. If all you want is performance, it really is that simple. Start throwing in more variables..fuel consumption, engine maintenance, durability, longevity..and it becomes complicated. Set your priorities and build accordingly.

[miketsouth]

Torque is for wrenches.... Torque is only half the equation..Power to the impeller is what it's all about.
jer
Why even bother Jer. You aint gonna change 'em with math (horsepower is work), reason (even mikeT can develope 500lbs torque with a wrench) or facts (Berkeley, American Turbine and all only use horsepower curves).
Maybe it is genetic.
I was enjoying and cataloging all this misinformation.
Using this misinfomation about Q/HP I was trying to work an analogy such that i could seperate the BS from fact in determining shoe/loader/rideplate setup for my SBC pickle. Now you gonna mess it all up.
I can hear it now
"hey Jer"
'yeah, punk'
"could you please put a torque window in the JPC"
'why would i do that, punk'
"so i can build an engine to go fast in my jet boat"
'well i suppose so, punk. Bend over and get me that math book out of the closet'
"which one, Jer: Calculus, Trig, Algebra or GEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEometry"
http://mywebpages.comcast.net/mikejet/forgettorque.JPG

[miketsouth]

Oh hell, I'll throw in my two cents:
Given that a jet takes more horse power to spin faster, the more power you have, the faster you go. Average torque over the RPM range means absolutely jack to a jet. It's about HORSE POWER.
here, here (applause)

[kojac]

ok My .02 cents.
I have been studying the torque/hp phenomenom for over the last 15 years or so and how they work in the jetboat arena.
What I have worked out is if you want to turn a motor to a higher rpm band to get maximum speed out of a jet boat is you have to build your motor to continue making torque up in the higher rpm band.
Higher Horsepower will naturally correspond to the higher torque when this happens.
The rpm an engine makes when torque falls off more than horse power gains is the rpm that the pump stops pulling.
We just witnessed on these forums a dne motor built for Diggler that has a horsepower rating in the 800 + on pump gas at 6500 rpm's.
If you look at the dyno sheet the torque drops off real quick compared to horse power above the 5500 rpm range. Diggler is going to run an a/b impellar and I don't believe that in it's present form it will not pull the a/b impellar above 5800 rpm's
Why? Because the torque drops off so quickly compared to the horsepower gain.
I had a 468 cu in engine that only made 675 hp at 6500 rpms and made peak 570 ft pounds of torque at 5400 rpm's. The motor turned a precision built race pump built by Don Bowers fully loaded to 6200 Rpm's at a speed of 104 mph in a heavy sterling tunnel.
The reason that the pump pulled in the upper rpm's was because the torque (even though not that high compared to some other peak torque numbers) did not fall off compared to the horsepower until 6200 rpm's.
The big cubic inch motors need a lot more air to fill the cylinders. It takes a lot of cam and head modifications to make the big cubic motors take in the adequate amount of air in the upper rpm range. Normally they fall off quickly and I believe that is why a lot of the big 540,575 inch motors make big hp numbers but don't deliver high rpm's on the pump. They simply run out of air at the lower rpm range.
The torque drops off radically. Unless you have a blower or big compression, big heads, and a big cam with springs that won't let the normal lake jetboat run up and down the lake without big problems.
I now have two 575 cubic inch engines and a 502 that run in the 6500 6900 and 6400 rpm' range pulling an a/b impellar. My friend has a 454 chevy that turns his b/c impellar to 6200 rpm's.
All of these motors have one thing in common. The torque doesn't fall of dramatically compared to horsepower until after 6200 rpm's.
If anybody has any data that says differently. Show me I want to learn something.
Kojac

[Ken F]

Well put!
Ken F

[miketsouth]

ok My .02 cents.
We just witnessed on these forums a dne motor built for Diggler that has a horsepower rating in the 800 + on pump gas at 6500 rpm's.
Diggler is going to run an a/b impellar and I don't believe that in it's present form it will not pull the a/b impellar above 5800 rpm's. Why?
I believe you are right about the rpm. The why: I just plugged the numbers into Jer's JPC.
Berkeley
6500RPM = 791 HP A/B
5800RPM= 565 HP
AT
6500=794 HP A/B
5800=566 HP
Of course this makes the monstrous assumption that the JPC is dead nuts. It is pretty good from what i can tell and gives at least a reference.
and here is how i look at it: (not considering torque at all, just RPM/Horsepower requirements)
He is too close to the edge. Any pump loading that would require more horsepower per RPM, and he will miss it completely. Any change that reduces his horsepower even a little (air conditions, maybe) and he will miss it. It will drag the engine down, but just how low i dont know.
As far as how low his engine will be dragged down ( i suppose), depends entirely on the horsepower curve. The sharper the curve the more it will be dragged down. Call it torque/rpm curve if you like, it is the same thing.
Something else that i thinks that happens when matching an impeller to higher rpm is loss of pump efficiency. This, (again i suppose) would affect the speed/HP of the boat, independant of the RPM. I dont have personal experience with this in a jetboat, but some small knowledge of pumps plus what i have read minus the BS.
When i look at the torque curves what you are saying about the torque curves is correct, If you look at the peak torque and just a little beyond, that is where the engine seems to run the pump at. Of course this is 'just' before the maximum horsepower too, almost every time.
Kojak, i had heard from others your use of the torque curve to identify RPM, so i tried it. It appears to be right.
And again i look forward to seeing you again at Anna.

[old rigger]

This thread is pretty good reading, no matter which side of the tourque/hp thing you stand on.
What I want to know is, with all the big dollar engines being built on the dynos now, with all the computer designed bottoms, with all the information avalilble in regards to pump flows and so on, why is the fastest drag jet boat is still something that ran back in the 80s? 'Rated X' ran several runs over 170 in BFJ back then with Dave Geonetti driving. That placecraft was fast until Billy jr. blew it over, amazing crash. He was lucky to live through it. 'Going Places' was almost just as fast. Hendersen ran an old cast iron hemi with iron heads too.
Is there no one running that class anymore? I don't know cause I haven't been to the drags in years. Seems with all the data guys like lvjetboy have, it'd be a record within reach for someone to grab.
So over at the NJBA site the BFJ class is wide open, no record at all. Someone would have to run a 148 to get the record.
the tourque/hp thing is kinda like the fast/quick thing too.
Great example would be the hull that cyclone and diggler have. That thing is decades old originating at eliminator, we had it at advantage, the banshee, and ultra has a shorter version, and I guess it's being used by some others too. We built a banshee with a single carbed sbc, low intake manifold, headers and so on. Hooked that to a OMC cobra outdrive. It certainly wasn't very quick out of the hole, but once she got on plane it was a terror. With the prop shaft set up even with the bottom of the center pod, it allowed the hull to really work as designed. Set the record in the ETII class and it still stands today, 116 and change in '88. It was a pretty ugly boat as far as hardware goes, no flash, no polished aluminum, no chrome, but it had a great set up.
Digglers and cyclones version's will certainly be quicker with, I would think, triple the horsepower than we had, killer pump set-ups, plus their hulls are a tad lighter being shorter. I'm excited to see what numbers they run on the top end. Be cool if they run close to what that banshee did or even better, faster.