Torque vs Horsepower?

[jim lee]

It seems that there will never be an answer will there? On and on the old fight continues. Well, its time to take sides and put your money where your mouth is.
http://www.banderlog.com/images/whichHat.jpg
What camp are you in? Horsepower (http://www.cafeshops.com/banderlog/102295)? Or would it be Torque (http://www.cafeshops.com/banderlog/102297)?
Now, when entering those internet flame wars, you can display your camp's official Torque Vs Horsepower battle gear. :)
-jim lee

[miketsouth]

If you are interested the thread starts here:
http://www.banderlog.com/cgi-bin/banderlog/dcforum/dcboard.cgi?az=read_count&om=3037&forum=DCForumID1
Lost of opinions and controversy. I got the 'torque dont move anything tshirt'

[Infomaniac]

If you are below 5,252 RPM you beter build for torque. Above 5,252 build for HP.

[Infomaniac]

Double post
[ May 27, 2003, 04:37 PM: Message edited by: Infomaniac ]

[Badboat1]

I agree with ya Info torque moves the mass and gets it going then horsepower takes over.I played with that as in impellers mine won't run till it gets on the pipe. 7000 rpm is were it likes to run.Had every impeller in it and turned some down and that is what it takes for every different setup boat/HP.
BB1

[Bense468]

Info is right 5,252 RPM is the magic number.

[Oldsquirt]

We went through this last summer about the "5252 rpm" deal. That number is actually meaningless in terms of performance. Purely an anomoly of the math involved. It is only the torque=hp point in our measuring system. Take the exact same engine, measure torque and power in metric units and that crossing point doesn't exist.
For a long time, I too was a believer....
[ May 27, 2003, 06:54 PM: Message edited by: OLDSQUIRT ]

[GlastronGuy]

OLDSQUIRT:
We went through this last summer about the "5252 rpm" deal. That number is actually meaningless in terms of performance. Purely an anomoly of the math involved. It is only the torque=hp point in our measuring system. Take the exact same engine, measure torque and power in metric units and that crossing point doesn't exist.
For a long time, I too was a believer.... Craig, don't keep us in supense. A believer in what?
wink

[Oldsquirt]

GlastronGuy:
Craig, don't keep us in supense. A believer in what?
wink That your "dual pumps" are what slow you down..... :D

[Infomaniac]

OldSquirt is correct about it being mathmatical.
A better term would be just to say "power" at a certain RPM.
There are still large differences in engine components designed to make power at low RPM's and those designed to make power at higher RPM's
Choose them to compliment the RPM's you intend to turn. If you decide to run it on a dyno to see what it does. You will need to speak dyno language. Torque and HP.
It just happens that Horsepower is the unit of mechanical measurement to rate engine power. It is measured on a dyno. Dyno's measure torque. You have to mathmatically convert torque to HP. wink
[ May 27, 2003, 07:44 PM: Message edited by: Infomaniac ]

[Trash]

Torque = whether or not you can move an object (work)
HP = how fast can you move it (work/unit time)

[Chris J]

Torque is good for acceleration and Horsepower is good for speed. Gotta have both.

[Chris J]

One more thought? When you give a torque spec at a giving RPM aren't you really talking about Horsepower? Kinda like saying I just Drove 60 miles and it took me one hour?
RPM gives torque (work) a value over time which is horsepower....Damm'it now you guys got me thinking. :confused:

[pops1]

jim lee:
It seems that there will never be an answer will there? On and on the old fight continues. Well, its time to take sides and put your money where your mouth is.
http://www.banderlog.com/images/whichHat.jpg
What camp are you in? Horsepower (http://www.cafeshops.com/banderlog/102295)? Or would it be Torque (http://www.cafeshops.com/banderlog/102297)?
Now, when entering those internet flame wars, you can display your camp's official Torque Vs Horsepower battle gear. :)
-jim lee JIM LEE-THE ONLY TIME THIS FIGHT COMES UP IS WHEN YOU TALK TO A SLOW ASS PROPERs.
NOW FAST JETS -BY THE WAY SPRAY PROPPERS JUST LIKE SKUNKS DO, THEN GO OFF EAT LUNCH,HAVE A NICE SOCIAL TALKING TO THE WOMAN,PUT THE COOLERS BACK IN THE BOATS, JUST ABOUT THE TIME THE PROPERS SLIP UP.
NOW I KNOW TONY THE JET BOAT GURU- STILL WILL NOT AGREE TO THIS, BUT SINCE THE SQUIRTERS SPANKED THE HYDRO @ THE 1,000 FOOTER THIS PAST YEAR. WE HAVE NOT HAD THEM VISITING OUR BOARDs -SO I SHALL CAST THE FIRST STONE-
PROPERS THOSE LEG CHOPING,HOLE DIGGING,STUFFING BOXES WHICH ARE SLOWER THEN SAIL BOATS ARE IN BIG TROUBLE AGAIN THIS YEAR- JETS- THE TORQUE GETS BIGGER WE GET MEANER AND SO DO OUR VANES!
NOW PROPERS YOU CAN CALL ME DAVE OR YOU CAN CALL ME POPs OR YOU CAN CALL ME FULL OF IT. BUT JETS AND TORQUE ARE GOING TO GIVE YOU SUCH BAD DREAMS.
JIM- SELL THEM HATS, AND TELL ALL THE ONES WHICH BUY THE WING, WING, WING,H/P HATS TO WATCH OUT FOR THE BIG DOGs "WHO DO NOT SPRAY LIKE A PUPPY"
THEY WILL SWAMP YOU AS THEY GO BUY.
(I WOULD HAVE SAID "AT THE LINE" EXCEPT IT TAKE'S PROPERS TWO OR THREE BOUNCES TO PLANE THE BOAT, SO THEY LEAVE THE LINE REAL EARLY. THATS WHY I SAID "GO BY" INSTEAD).
NOW THIS COULD START SOMETHING! HA HA

[LVjetboy]

"Dynos measure torque"
Are you sure about that?
:)
jer

[Infomaniac]

LVjetboy:
"Dynos measure torque"
Are you sure about that?
:)
jer No doubt about it.
pops 1 - They had to shorten the race track for ya huh? Crashed a few of them squirt boats pushing it to the edge also.

[Bense468]

Nobody said anything about weight on here. I am suprised. Build an all aluminumn blown stroker small block. Put it in a light layup. That small block may have less torque then the big block, but weighs less, and just may get out of the hole faster then that big block and would be gone.

[BK]

Bense468:
Nobody said anything about weight on here. I am suprised. Build an all aluminumn blown stroker small block. Put it in a light layup. That small block may have less torque then the big block, but weighs less, and just may get out of the hole faster then that big block and would be gone. That may be true but I dont think the weight of a motor has anything to do with how much hp or torque its going to put out or how many rpm's its going to spin. Am I wrong here?

[Bense468]

No, it has nothing to do with the motor itself. But you need torque to move mass. The lighter the boat. The less torque you need to get the thing moving. Get what I am saying. Its all about mass. If your setup is heavy you need gobs or tq to get you out and going. The lighter the setup the faster you are on plane and HP can take over. Someone please correct me if I am wrong.
[ May 28, 2003, 04:28 PM: Message edited by: Bense468 ]

[BK]

Hey Bense you make a good point, what your saying seems to make sense to me. idea

[Hal]

You have to consider a jet boat is like running your engine on a dyno. Its the same thing. You need a lot of torque to get the rpm (more water pressure) out of your pump not HP.
Read this (http://auto.howstuffworks.com/horsepower2.htm)
[ May 28, 2003, 05:10 PM: Message edited by: Hal ]

[Sangster]

Now how do you argue with that... wink

[MAXIMUS]

I will settle for my 540... I get hp & torq!!! then I don't have to choose... :D :D My dyno says I am hauling ass!!!! :)

[MikeF]

You want to position the amount of torque (in the rpm range) to be able to turn the larger impellers from 5252 to ++++. The more TORQUE you have, the more rpm you can turn a given (larger) impeller.
You get more torque by adding an air pump to better fill the cylinders with the largest amount of air and fuel possible in the correct ratios for the largest push on the crank (torque) once it is ignited :D .
I think boxed smile_sp

[MikeF]

Not to get too far off the subject.....but who can explain the 18,500 rpm (well above 5252) revs that the F1 cars are able to turn and why do they make them rev sooooooooo high eek! wink .

[Hal]

They are not heavy enough to need torque to make them move. Its more like this. Who needs Torque when your weight to HP ratio is 2 to 1 (http://www.shaolink.net/cositas/patinete.wmv) 23000 RPM :D
[ May 28, 2003, 07:17 PM: Message edited by: Hal ]

[Bahner18]

"5252" That is a crazy number!! If you look at Dyno sheets youll notice that most engines cross at 5252 ?why? Well its part of the equasion to measure HP.
(Measured Torque) times (RPM performed at)divided by 5252 equals HP
Yah my spelling sucks

[Hal]

What does that mean? :confused: :confused:

[Bahner18]

You around hal?

[LVjetboy]

Amazing how urban legend lives on, despite evidence to the contrary. I guess if you grow up believing something, hard to change?
Like those who swore the earth was flat.
OldSquirt explained clearly the magic 5252 myth, but do readers believe? No. Still the myth lives on. "You need torque below 5252, and power above." Ya whatever. Tell that to the metric guys.
So also the dyno. "We measure torque on the dyno not power, so torque must be more important!"
Think about it.
What do you REALLY measure on a dyno? Pressure in some cases. Temperature in others. And stain (displacement) on others still. Then that measurement (not torque directly) is mathematically or by calibration combined with a moment arm (if used) to derive torque. So what?
Does that make torque any less important than the force or temperature or pressure directly measured by which torque is derived from? No. So also with power. Because power is derived from torque plus rpm...another measurement, does that make it any less important than torque? No. The fact that torque is derived from strain or pressure and power is derived from strain or pressure and rpm has no meaning to this thread. These "derived from" arguements are lame and deflect reasoning from the real truth...that being, which property (torque or power) is more important to determining performance.
jer

[jweeks123]

nice finish there lv!
jw

[Rexone]

is that english :confused:

[LVjetboy]

Ya, "Get him Rex!"
:)

[Infomaniac]

I was not talking about a scientific explaination of what the dyno measures. I stopped at the measurement actually used to rate the engine.
To get scientific we can go all the way to the chemical energy in the fuel converted into heat energy by combustion. That heat energy transformed into a reciprocating mechanical energy. That reciprocating motion converted to a rotational mechanical motion. This is given to the dyno.
We can start at the beginning of dinosaur crap and remains converted into oil if necessary.
Is this fun or what? I think some of us need a life. Myself included.

[Cas]

I don't believe you can get the hp you're looking for without the necessary tq at a particular rpm.

[Bense468]

The bottom line is look at torque. It moves mass. HP carrys the mass after the torque gets it moving. I have no clue what Jer said. Most of the time I don't. But the heavier you are the more torque you need to get the boat moving before HP takes over to carry that momentum(SP). So weight plays a big factor. The lighter the vehical/boat the less torque it needs to push it to that point where HP takes over to carry it.

[FingerTight]

So, here is the point that I continually see missed in these discussions.
Yes tq gets mass moving, what happens when you hit the gas in your boat? The RPMs jump way up and the boat begins to move. The only time tq was a working force was when the motor needed to begin that drive system spinning. Once it was spinning, all the "mass" that it needed to get started, had been started, tq is no longer a factor.
At this point it is up to hp to keep that mass spinning.
So how does tq relate (IMHO), the more tq you have, the larger imp. you can spin up. Larger imp. = more speed.
my .03$

[LVjetboy]

FingerTight is right.
Some confused by car dynamics thinking same as jet boat dynamics.
A car engine is directly connected to the road assuming traction and no clutch spin. Therefore, the car engine has to deal with the mass of the car as it spins it's way to peak hp.
By contrast a jet boat engine is directly connected to an impeller and spins quickly to maximum hp regardless of boat mass. There's a difference here in what "mass" you are accelerating, and the effect of that "mass" on engine performance as FingerTight posted.
"I have no clue what Jer said."
Is that pretty clear Bense? If not let me know. These are my opinions right or wrong and I'd be happy to debate them, just wanna make sure I clearly state my thoughts for you.
First ya got to read carefully...past the earth is flat stuff :) But if my earlier post unclear, then please read the following...
Urban myth:
"We measure torque on the dyno not power, so torque is more important!"
This is a myth that circulates both car and boat forums from time to time...
Truth:
Dynos actually measure things like force or pressure (sometimes temperature) and convert to torque by multiplying by the lever arm. I'm assuming it's clear what a lever arm is Bense? The mathematical relationship is:
Torque = F X d where d is the lever arm.
Those dyno measurements of force or pressure can just as easily be converted to power by multiplying by lever arm and measured rpm. So the myth implying that torque is more important because somehow it's a more basic measurement on the dyno is bogus. Both torque and power in the end are "mathematically derived" from what is actually measured on the dyno.
Note: The above "truth" does not imply power is more important, just that neither power or torque is more important based on what is measured on a dyno or how that quantity is derived.
There are other (non-bogus) reasons for which property (torque or power) is more important to jet boat performance, but I won't get into that right now :)
Info, I stopped short of dyno crap too. That and the meaning of life. Just focusing on which engine property is more important to jet performance...and exploding urban myths...
:)
jer
[ May 29, 2003, 02:59 PM: Message edited by: LVjetboy ]

[superdave013]

pops1:
jim lee:
It seems that there will never be an answer will there? On and on the old fight continues. Well, its time to take sides and put your money where your mouth is.
http://www.banderlog.com/images/whichHat.jpg
What camp are you in? Horsepower (http://www.cafeshops.com/banderlog/102295)? Or would it be Torque (http://www.cafeshops.com/banderlog/102297)?
Now, when entering those internet flame wars, you can display your camp's official Torque Vs Horsepower battle gear. :)
-jim lee JIM LEE-THE ONLY TIME THIS FIGHT COMES UP IS WHEN YOU TALK TO A SLOW ASS PROPERs.
NOW FAST JETS -BY THE WAY SPRAY PROPPERS JUST LIKE SKUNKS DO, THEN GO OFF EAT LUNCH,HAVE A NICE SOCIAL TALKING TO THE WOMAN,PUT THE COOLERS BACK IN THE BOATS, JUST ABOUT THE TIME THE PROPERS SLIP UP.
NOW I KNOW TONY THE JET BOAT GURU- STILL WILL NOT AGREE TO THIS, BUT SINCE THE SQUIRTERS SPANKED THE HYDRO @ THE 1,000 FOOTER THIS PAST YEAR. WE HAVE NOT HAD THEM VISITING OUR BOARDs -SO I SHALL CAST THE FIRST STONE-
PROPERS THOSE LEG CHOPING,HOLE DIGGING,STUFFING BOXES WHICH ARE SLOWER THEN SAIL BOATS ARE IN BIG TROUBLE AGAIN THIS YEAR- JETS- THE TORQUE GETS BIGGER WE GET MEANER AND SO DO OUR VANES!
NOW PROPERS YOU CAN CALL ME DAVE OR YOU CAN CALL ME POPs OR YOU CAN CALL ME FULL OF IT. BUT JETS AND TORQUE ARE GOING TO GIVE YOU SUCH BAD DREAMS.
JIM- SELL THEM HATS, AND TELL ALL THE ONES WHICH BUY THE WING, WING, WING,H/P HATS TO WATCH OUT FOR THE BIG DOGs "WHO DO NOT SPRAY LIKE A PUPPY"
THEY WILL SWAMP YOU AS THEY GO BUY.
(I WOULD HAVE SAID "AT THE LINE" EXCEPT IT TAKE'S PROPERS TWO OR THREE BOUNCES TO PLANE THE BOAT, SO THEY LEAVE THE LINE REAL EARLY. THATS WHY I SAID "GO BY" INSTEAD).
NOW THIS COULD START SOMETHING! HA HA This is a great post. :D

[LVjetboy]

Now pops posts a challenge...just need a couple brews and reread several times to get the flow.
jer

[Duane HTP]

"Yes tq gets mass moving, what happens when you hit the gas in your boat? The RPMs jump way up and the boat begins to move. The only time tq was a working force was when the motor needed to begin that drive system spinning. Once it was spinning, all the "mass" that it needed to get started, had been started, tq is no longer a factor."
We're not talking of the mass of the impeller here. We are talking about the mass of water that the impeller is moving.
[ May 29, 2003, 05:18 PM: Message edited by: Duane HTP ]

[LVjetboy]

I think that's a good point Duane.
There's certainly a mass to the water moving through the impeller.
But, how does that mass compare to the mass of a jet boat? And how does a jet boat engine, reacting to impeller and water mass loading, compare to a car engine, reacting to driveline and car mass loading? I think differently. And the answer may very well make a difference to this discussion.
Consider a 10,000 lbm jet boat. If the mass of water being accelerated through the impeller was equal to the mass of that elephant jet, then the engine would likely spin very very slowly to peak hp, if ever? My guess is, even if you lash your jet to a dock = the mass of the earth (stay with me here Bense), the engine will spin to near peak hp regardless of the mass of the dock and the earth connected to it. Don't know, haven't tried it. But try that with a car :)
So...comparing the mass of a jet boat to the mass of a car...both being accelerated through their different drive designs, and each reacting to different engine speed vs vehicle speed constraints, may be misleading.
Just some thoughts to add fuel to the fire,
jer
[ May 29, 2003, 06:15 PM: Message edited by: LVjetboy ]

[Hal]

I agree with LV and Duane. To The only way to compare a jet boat to a car you would have to look at it like this. In a jet boat it takes very little torque to just floor it and run your engine RPM up and spin the impeller. That is untill you start moving the boat and the loader starts stuffing the the water into the pump and the pump starts building pressure. That is why a jet pump is like a dyno. The faster you go the more pressure the pump will build and the more torque it needs to continue to gain RPM. It would be like in a drag car only start appling your brakes after the 1/8 mile and make the torque instead of the HP take you to the end of the 1/4.
Does that make any sense? Thats how I've always looked at it. :D

[LVjetboy]

Hal,
I wondered too about the "stuffing" effect.
Now I don't claim to have all the answers, even though some think I do by my posts :) But from what I've seen of racers data plots (thanks Duane, Bear, Bp, KZ and others) jet speed and intake pressure or loading has little affect on rpm. Once past launch transients. If that's true? Then intake "stuffing" and how that influences engine loading is minimal (not neglegible just minimal) and not a dominant factor in hp vs Q discussions.
But that's just a guess on my part. What do you think?
jer
[ May 29, 2003, 06:19 PM: Message edited by: LVjetboy ]

[Hal]

Jer,I didn't mean that stuffing effect would cause more load to be applied. I just used that term meaning that when the boat was up to speed and the pump was fully loaded is when you start needing torque to drive the pump. You hit the nail on the head when you said tie your boat to the dock, because that would be the same as putting your engine on a dyno. It would be like like starting your car againist a brick wall and going thru the gears. (with street tires?) :)
[ May 29, 2003, 06:35 PM: Message edited by: Hal ]

[Builder]

You say that torque becomes unnessesary after the water gets flowing ,well what about the large problem of forcing it out of the reduced opening in the rear of the pump.It takes Torque to move that mass also.It just doesn't flow like a lazy river out the back. Torque moves mass

[Hal]

Thats kind of what I was saying, When the pump gets loaded meaning its building pressure because it has to move all that water thru a little hole, the motor starts needing torque to turn the impeller againist that pressure.

[Old Guy]

Just curious, have any of you river jetters ever tied a rope from the back of your boat to a bridge to see if WOT turned the same rpm when the boat wasn’t moving? We would know for sure if intake “stuffing” was fact or fantasy.
old

[LVjetboy]

Builder,
I never said torque was unnecessary after water gets flowing, in fact torque will still be there. Unless you have no friction or losses and no acceleration? Pretty unlikely for jets or anything else in the real world.
On the "torque moves mass" thingy. A common mantra echoed by many in an attempt to answer the dilemma. But think about it, what does that really mean? Torque doesn't do sh*t unless there's motion. Consider the rusted bolt. Turns out the "motion" part, and exactly how fast that motion is, is a more important consideration to performance in the end. The statement "torque moves mass" is a catchy phrase, sounds pretty good, but doesn't go very far in explaining whether we should focus on power or torque to determine jet boat performance. The focus of this thread.
Turns out jets are more like rockets when it comes to performance. Ever try'n figure out the torque of a rocket? There is none of course. Just power and thrust modified by mass = acceleration. Think about it. Study it if you must.
Yes, in the real world, if there's circular motion involved, you'll also have torque applied. And guess what? You'll also have power applied. The question is, "Which term best describes the performance of that circular motion?" Turns out power. Because power not only describes how much muscle (torque) is applied but also how fast that muscle is being applied. This is a key point. Not explained by the "torque moves mass" mantra. And it turns out, also not a trivial thing in the performance world.
So too in the jet boat world. You focus on torque alone you get half the story. Not that you get nothing, only that you get half the story.
You focus on power and you get the whole story. That being both the amount of torque and the rate at which that torque is applied...not a trivial thing when talking about overall system performance i.e., the speed of a jet hooked to an engine with certain power capabilities.
jer
[ May 29, 2003, 08:35 PM: Message edited by: LVjetboy ]

[LVjetboy]

OldGuy,
I'm guessing none? How about you try and let us all know what happens.
:)
jer

[Johnwithjm]

So where did Jim go :D :D

[MikeC]

No doubt there is a torque requirment to turn a pump. But in fact, when you say HP we are refering to torque as being a big part of that, however. I heard a young kid explain it very well (in my opinion) somewhere on the net a couple of years ago. He understood the relation ship pretty well when he compared it to his 2 cycle dirt bike. When you rev that sucker up to 10k and dump the clutch, it's the HP (as in, a mass spinning very fast) that spins the knobby and blasts you out of a berm........ This is just how I think of it. Now compare that to a 4 cycle, who, cube for cube, will win the race?
MikeC

[kojac]

Two things I discovered about one of my jetboats. 1. When I replaced a 1/4 inch lower shoe on the intake it dropped the rpm"s from 6900 to 6450. A loss of approximatly 100 horsepower. So stuffing the pump would certainly seem to have an effect.
2. When measuring the rpm's of several motors on the dyno I found at the rpm the torque drops more than the horsepower increases is where the pump impellar will stop turning in rpm's. The exception is when the impellar is inproperly sized too small. If at 6000 rpm's the ft#'s of torque drop more than the horsepower increases than the pump will not turn more than 6000 rpm's.
That would indicate that the measure of torque is where we should be looking. One of my 572's makes 974 hp at 7200 rpm' but the torque factors start to drop off more at 6900 rpm's than the horsepower increases so the pump stops turning at 6900rpm's. Maybe Duane or Dave could elaborate on this phenomenem.
Kojac.... :)

[jweeks123]

LVjetboy
You focus on power and you get the whole story. That being both the amount of torque and the rate at which that torque is applied...not a trivial thing when talking about overall system performance i.e., the speed of a jet hooked to an engine with certain power capabilities.
just tryin to help out here with some highlight, lv.
jw
[ May 30, 2003, 01:04 AM: Message edited by: jweeks123 ]

[Chris J]

Just in case your looking for more info in this subject, and if your reading this post you are!
http://www.grapeaperacing.com/GrapeApeRacing/tech/miscpower.cfm

[OMEGA_BUBBLE_JET]

just some food for thought. If torque was the primary objective in engine building for jet boats wouldn't we all have diesels in our boats? I think the two are dependant upon one another but bottom line is you need hp for top speed.
Omega

[LVjetboy]

There's lots of good links about power and torque...some better than others. Remember as you read, the mass the jet boat engine reacts to is not the same as the mass the car engine reacts to. So you'll see comments from time to time geared more to car performance than jet performance.
Kojac, that's a big drop in rpm. Before you dropped the shoe was your pump fully loaded? My comments about stuffing not having a big effect on rpm were meant for a fully loaded pump. Any slipping or cavitation from a non-fully loaded pump may explain the big drop in rpm you saw.
Let's look at some real data* Here's a run with rpm in red. Notice after 13 seconds (pump loaded - engine off limiter) there's virtually no change in rpm for the remainder the run. Even though both intake pressure and jet speed increase dramatically. Rpms stay nearly the same...about a 50-75 rpm drop from 13 to 17 seconds.
http://users.lvcm.com/lvjetboy/MPDrun.gif
This seems to tell me that once an impeller is fully loaded, changes in intake pressure from "stuffing" or jet speed have little influence on engine rpm or engine loading. What do you all think?
jer
[ May 30, 2003, 10:50 AM: Message edited by: LVjetboy ]

[bp]

you can see very slight changes in engine rpm with suction pressure changes, certainly not 500 rpm. depends on how big a suction pressure change you're creating. it's very likely the 500rpm drop occurred due to unloading or perhaps cavitation at the higher rpm, and now there's more than enough. it would be interesting to know how much speed dropped with the 500 rpm drop, if it dropped at all. dropping the shoe .250" is way more than i'd ever try at one time.

[Chris J]

Hey LV can you give us more info on the graph. What are the other data points and what are the units measured in and peak readings in psi, mph ect. Interesting stuff .... I like this concept of working with facts and numbers. :cool:
Thanks
Chris

[LVjetboy]

Hi Chris,
I cut off the other scales, so rpm's the only one showing. I'm thinking this is your run bp? If Bp doesn't mind I'll post the rest of the numbers.
Red = Rpm
Green = Bowl press
Grey = Speedo
Yellow = Fuel press
Black, Dark blue & purple = intake press (3 lines)
There's also a ppl battery voltage and vacuum line
jer
[ May 30, 2003, 01:12 PM: Message edited by: LVjetboy ]

[FingerTight]

Old Guy:
Just curious, have any of you river jetters ever tied a rope from the back of your boat to a bridge to see if WOT turned the same rpm when the boat wasn’t moving? We would know for sure if intake “stuffing” was fact or fantasy.
old Interestingly enough, I have run this experiment on a smaller "jet boat". If one holds back a 550 jet ski and floors it, the engine will run to within a nats ass of top end, while the boat does not move.
I think the comments about HP being the overall picture, with Tq a function of HP are right on. Even with the added pressure, it is the HP that keeps this spinning mass going. (mass being the imp., the water it is pushing, and the pressure it is pushing against).
The only time Tq is involved is getting this three part "mass" initially started.

[jim lee]

"Where's jim?" I'm here, reading along and seeing where this is going. Seeing who takes sides where. On the Banderlog version of this thread there were a lot of interesting and quotable statements. Not so many here yet. But then the Banderlog version went on for 164 posts. I think it was an alltime record.
Here's some hats with the different statemets on them. Perfect to wear when composing posts of this nature! wink
http://www.banderlog.com/images/pickYourPosion.jpg
Do you have the conviction, nay the Courage! To actually wear what you state on the net?
If you do, then.. Pick your poison (http://www.cafeshops.com/banderlog/102500)!
-jim lee

[LVjetboy]

Any question which side I'd take Jim?
:)
The other interesting thing about your experiment FT, is if rpm (engine loading) is mostly independent of jet boat speed, is rpm also independent of jet boat weight? I have a reliable source with data that says yes. Logic also leads to the same conclusion.
So...if the engine's blind to hull speed and weight, then the thrust it produces through the pump is also independent of hull speed and weight.
So getting maximum thrust (= performance) an exercise in matching engine maximum output power to impeller required input power so that the most power possible is applied to the impeller. Neglecting cut size loss of course.
But should we neglect cut size loss? Who knows the answer to this?
If cut size loss is defined by x hp loss per rpm per cut size, would downsizing from an A to a D loose more hp than gained by placing the engine higher on the power curve? Easy to figure if you had pump efficiency data.
What if each impeller mfg. published efficiency curves to show this loss?
Oh never mind. Most don't even publish impeller power curves. Silly me.
jer

[bp]

jer, i don't mind if you use or describe the run, but it's not one of mine :D

[LVjetboy]

Oops. I just looked a little closer at the speed thing, a tad faster huh?
:)
jer

[LVjetboy]

I'm going to contact Berkeley and see if they have performance curves for their pump...something that shows efficiency change with rpm's and maybe even cut size. (not just power curves) Surely they should have that, right?
jer

[kojac]

LVjetboy:
There's lots of good links about power and torque...some better than others. Remember as you read, the mass the jet boat engine reacts to is not the same as the mass the car engine reacts to. So you'll see comments from time to time geared more to car performance than jet performance.
Kojac, that's a big drop in rpm. Before you dropped the shoe was your pump fully loaded? My comments about stuffing not having a big effect on rpm were meant for a fully loaded pump. Any slipping or cavitation from a non-fully loaded pump may explain the big drop in rpm you saw.
Let's look at some real data* Here's a run with rpm in red. Notice after 13 seconds (pump loaded - engine off limiter) there's virtually no change in rpm for the remainder the run. Even though both intake pressure and jet speed increase dramatically. Rpms stay nearly the same...about a 50-75 rpm drop from 13 to 17 seconds.
http://users.lvcm.com/lvjetboy/MPDrun.gif
This seems to tell me that once an impeller is fully loaded, changes in intake pressure from "stuffing" or jet speed have little influence on engine rpm or engine loading. What do you all think?
jer

[kojac]

Kojac, that's a big drop in rpm. Before you dropped the shoe was your pump fully loaded? My comments about stuffing not having a big effect on rpm were meant for a fully loaded pump. Any slipping or cavitation from a non-fully loaded pump may explain the big drop in rpm you saw.
LVJetboy, I didn't think that the pump was fully loaded and that's why I installed a deeper shoe.
I ordered a .125 deeper shoe and the supplier sent the .250 shoe so I figured what the hell I'll try it and if it doesn't work I will have the shoe reduced. I have just recieved the new shoe at .125 and will try it when the rain finally stops. The deeper shoe worked great when I was running in choppy water but had a tendency to parachute in glass. I felt like the boat had a tendency to flip forward and was not under control when I slowly accelerated.
Generally I would not recommend going over .030 lower at a time to insure that you are getting the best performance gains. After measuring the bottom configuration and depth of the bottom of the keel of the bubble I determined that .125 would result in the optimum efficiency. I concurred with Gregg Shuemaker of GS marine and Tom Papp who built the stealth.
I'll let you know when I get some results.
What instruments did you use to get your test results? Your graph does not show specific data numbers for speed,bowl pressures, rpm's, and intake pressures. I understand if this information is considered proprietary.
thanks Kojac... :)

[LVjetboy]

Kojac, those not my numbers but shared from a racer on the board awhile ago. Maybe KZ? If I get permission, I'd be happy to post all the numbers.
jer

[bp]

jer, that is not a run of kz's. that is a run captured by an mpd prepped edelbrock quikdata system (mpd being an edelbrock distributor). although i have a hunch whose run it was, jack is the only one who knows. yes, the speed is a little up from mine, but those 400lb hulls always get my 750lb hull on the top end :D
you know, you can easily make shims out of .03, .06, .09 and .125 aluminum that will fit between you're intake and shoe. just slowly shim the thing down until you find the right depth. no one can tell you "exactly" where shoe depth should be for your particular boat. the absolute best i've ever seen at giving a "ballpark" shoe depth is jack, end of story. but, if you have decent instrumentation, and know what it means (in conjunction with other information), you can fine tune it.

[Builder]

TORQUE MOVES MASS
LVjetboy:
Builder,
I never said torque was unnecessary after water gets flowing, in fact torque will still be there. Unless you have no friction or losses and no acceleration? Pretty unlikely for jets or anything else in the real world.
On the "torque moves mass" thingy. A common mantra echoed by many in an attempt to answer the dilemma. But think about it, what does that really mean? Torque doesn't do sh*t unless there's motion. Consider the rusted bolt. Turns out the "motion" part, and exactly how fast that motion is, is a more important consideration to performance in the end. The statement "torque moves mass" is a catchy phrase, sounds pretty good, but doesn't go very far in explaining whether we should focus on power or torque to determine jet boat performance. The focus of this thread.
Turns out jets are more like rockets when it comes to performance. Ever try'n figure out the torque of a rocket? There is none of course. Just power and thrust modified by mass = acceleration. Think about it. Study it if you must.
Yes, in the real world, if there's circular motion involved, you'll also have torque applied. And guess what? You'll also have power applied. The question is, "Which term best describes the performance of that circular motion?" Turns out power. Because power not only describes how much muscle (torque) is applied but also how fast that muscle is being applied. This is a key point. Not explained by the "torque moves mass" mantra. And it turns out, also not a trivial thing in the performance world.
So too in the jet boat world. You focus on torque alone you get half the story. Not that you get nothing, only that you get half the story.
You focus on power and you get the whole story. That being both the amount of torque and the rate at which that torque is applied...not a trivial thing when talking about overall system performance i.e., the speed of a jet hooked to an engine with certain power capabilities.
jer
[ June 02, 2003, 02:50 AM: Message edited by: Builder ]

[Builder]

So when will I be convinced?
LVjetboy:
Builder,
I never said torque was unnecessary after water gets flowing, in fact torque will still be there. Unless you have no friction or losses and no acceleration? Pretty unlikely for jets or anything else in the real world.
On the "torque moves mass" thingy. A common mantra echoed by many in an attempt to answer the dilemma. But think about it, what does that really mean? Torque doesn't do sh*t unless there's motion. Consider the rusted bolt. Turns out the "motion" part, and exactly how fast that motion is, is a more important consideration to performance in the end. The statement "torque moves mass" is a catchy phrase, sounds pretty good, but doesn't go very far in explaining whether we should focus on power or torque to determine jet boat performance. The focus of this thread.
Turns out jets are more like rockets when it comes to performance. Ever try'n figure out the torque of a rocket? There is none of course. Just power and thrust modified by mass = acceleration. Think about it. Study it if you must.
Yes, in the real world, if there's circular motion involved, you'll also have torque applied. And guess what? You'll also have power applied. The question is, "Which term best describes the performance of that circular motion?" Turns out power. Because power not only describes how much muscle (torque) is applied but also how fast that muscle is being applied. This is a key point. Not explained by the "torque moves mass" mantra. And it turns out, also not a trivial thing in the performance world.
So too in the jet boat world. You focus on torque alone you get half the story. Not that you get nothing, only that you get half the story.
You focus on power and you get the whole story. That being both the amount of torque and the rate at which that torque is applied...not a trivial thing when talking about overall system performance i.e., the speed of a jet hooked to an engine with certain power capabilities.
jer

[LVjetboy]

Right after my next post...

[Infomaniac]

bump for first page of archive