[jpizzle440]

ive sifted through alot of threads and probably havent found the right ones or all the ones i need to read. so if you know a good thread i need to read let me know. anything to do with pump parts and impeller/motor set ups/combos with reasoning behind what the parts accomplish and how, i will read.

little info - my friend is an engineer and im an over paid welder we are both smart in diff areas and, both grew up working on stuff ourselves because we have the know how to figure it out and like to save money. we like to butt heads with each other on ideas until we figure it out the same. kinda like math, prove each other right or wrong. me i grew up around jet boats and until this year my knowledge was "blue print and balance it all, get a jet-o-vator for trim adjustment and haul a$$" i been around alot of diff boats that had diff droop snoots and diff pumps and big motors in expensive pickle forks with expensive pumps that got there a$$'s handed to them by stock motors and stock pumps. 26 years of this i bought a bought a boat that had a wedge on the pump and i was dumb struck, never seen or herd of a wedge. kind of still dont understand the purpose other than a cheaper way to get more speed with out the adjustment of a jetovator.

"our arguement"

we are talking about the same boat pump and impeller of any make you choose.
we both understand in our own way limitations and torque curves of impellers.
our arguement started off as making a small block motor work with the same impeller made for a big block set up
we both agree that if you build the motors to match the same torque/hp (power) range that it will work fine
were we dont agree is here. he says the if that impeller was made for say 550lbs of power at 5500rpm he dont see why you cant get more thrust out of another motor, wether it be big or small block, with the power range surpassing 5500 carrying the power band another grand or two and put out more thrust on that same impeller being as the charts are a ruff guide.
in my understanding of the impellers, the power range of the motor has to match the power range of the impeller. so if i have a boat with a bb and an impeller matched to its dyno at peak power of 5500. he says that his bb or sb race motor that can carry the torque/hp (power range) another 2 grand more will put more thrust on the same impeller. to my understanding the motor should work fine but i think you need a different cut to get all the thrust you can with the motor spinning that extra 2000 rpms more or your just wasting energy.

also we are bumping heads on changing the bowl and nozzle setup to compensate for that extra 2grand. he thinks you can and i think your just changing the use of the max thrust that impeller is giving you.

we agree and disagree but can prove each other wrong or right.

are we both wrong or are we both right? i dont want no bashing each other it distracts my train of thought. just facts, theories, and personal experience on how it works. prove us both wrong prove us both right. there is no stupid question just uninformed people. and like i said if this has already been argued and settled on another thread i havent found it yet.

 

[Budweiser]

I like this type of discussion. I'll bite...

"our arguement"

we are talking about the same boat pump and impeller of any make you choose.
we both understand in our own way limitations and torque curves of impellers.
our arguement started off as making a small block motor work with the same impeller made for a big block set up

Slight modification to the train of thought. Small block or big block is not really of importance at this point AND I would stray from the thought that a certain impeller is made for a big block or a small block. Sure, one cut or another may be better suited to the "average" or stock replacement small or big block, but as you well know in this sport... nearly no one is running a stock replacement engine. They are all different. Basically, there is not an "impeller made for a big block"

we both agree that if you build the motors to match the same torque/hp (power) range that it will work fine
were we dont agree is here. he says the if that impeller was made for say 550lbs of power at 5500rpm he dont see why you cant get more thrust out of another motor, wether it be big or small block, with the power range surpassing 5500 carrying the power band another grand or two and put out more thrust on that same impeller being as the charts are a ruff guide.

Small correction: Torque is force not power... So 550 ft lbs of torque(force) at 5500rpm is 576 Horsepower (Torque x RPM ÷ 5252 = HP)

Your wording is a little difficult to understand in order to provide a direct answer...

Forget about torque and power at the moment. If your current engine spins the impeller 5500 rpm and you put another engine in that's able to spin the pump 6500-7500rpm... the pump will move more water, provide more thrust, and your boat will accelerate harder and go faster. Bottom line.

I kinda get the feeling both of you get that and it doesn't solve your debate... read on.

in my understanding of the impellers, the power range of the motor has to match the power range of the impeller. so if i have a boat with a bb and an impeller matched to its dyno at peak power of 5500. he says that his bb or sb race motor that can carry the torque/hp (power range) another 2 grand more will put more thrust on the same impeller. to my understanding the motor should work fine but i think you need a different cut to get all the thrust you can with the motor spinning that extra 2000 rpms more or your just wasting energy.

The impeller and horsepower curves do not absolutely have to match. It's not a "has to match" kinda thing. Loosely speaking any automotive engine will spin any cut impeller at least enough to pump water and move a boat. However, you are right in that, to get optimum performance the impeller should allow the engine to achieve an rpm at or near where peak horsepower occurs in it's power band.

So, from what you've said, here's my best interpretation of what I think you and your friend are saying...

(hypathetically) There is a boat, and the engine in your boat is a Big Block that dyno'd 576hp @ 5500rpm (from above), and while the boat is in operation, the impeller will hold the rpm's at 5500rpm. Your buddy has a Small Block in his garage that just happens to make the same exact horsepower but at a higher rpm, 576hp @ 7500rpm.

If you or your friend thinks you could drop his engine in the boat without making any other changes and spin the pump 7500rpm... Someone would be VERY disappointed. Unless, for some fairy tale reason, it also makes 576hp at 5500rpm... it wouldn't even pull the impeller close to 5500. Your boat would go slower.

Now,technically speaking and not taking into account for various possible losses, if you put an impeller in that absorbs 576hp @ 7500rpm... now your back to square one, pumping the same amount of water as before with the other engine/impeller combination.

If you spin any impeller a certain rpm it will pump a certain amount of water. If you spin it faster it will pump more water. It requires more horsepower to pump more water.

Not sure what you/your friend means by "can carry the torque/hp (power range) another 2 grand", but if it means makes [email protected] and makes even more at higher rpm's... Then, yes, it will spin the impeller beyond 5500.

Time for charts.

Looking at the chart above, an "A" impeller would be a great choice for an engine that makes 576hp @ 5500rpm.. To spin that same impeller to 6500rpm, your engine will have to make 875hp @ 6500. If you want to spin it to 7500, that's going to have to be one hell of a fairy tale Small Block! It's gonna have to push somewhere in the neighborhood of 1400-1500hp! That's a SERIOUS engine, even in Big Block terms.

You said "we both understand in our own way limitations and torque curves of impellers". We're talking about a 1000hp discrepency. I gotta say, I'm not sure either of you are near understanding... Yet. LOL

Or, maybe I just don't understand what your discussion is really about.

Bottom line is a Small Block will have to make the same horsepower at the same rpm as a Big Block to spin the same impeller the same rpm. Not too tall of an order if your talking about a 300-400 horsepower stock replacement type of Big Block, but as they say... No replacement for displacement...

also we are bumping heads on changing the bowl and nozzle setup to compensate for that extra 2grand. he thinks you can and i think your just changing the use of the max thrust that impeller is giving you.

This part is beyond me. Someone else will have to speak about this type of tuning, which I assume has a lot to do with the package as a whole... Intended use, weight, power, specific hull design, etc.

 

[bp298]

good job seth. i had no idea what he was asking.

 

[Budweiser]

good job seth. i had no idea what he was asking.

Thanks, I appreciate it. Still not sure if I addressed exactly what he's looking for either.

 

[Master Sergeant]

Nice answer!

 

[gn7]

Thanks, I appreciate it. Still not sure if I addressed exactly what he's looking for either.

I'm not sure either Seth.
If the impeller was cut for engine #1 and a peak of 5500, and the second engine made the same torque at roughly the same RPM and still made MORE torque further up, then fine.

But if he is saying the second engine makes its peak at 6500, or 7500, but the torque is the same, just at a higher RPM, thats going to require a different impeller cut.

The only reason I think thats the question is the SBC/BBC comparison.
As in, can a impeller for a BBC making 500lbs at 5500 be used behind a SBC making 500lbs at 6500 or 7500, and move more water and thrust.

The answer is right there in red. There is no such thing as a free lunch!
Chances are the SBC would never reach peak torque with the same impeller



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[jpizzle440]

yes good answer budweiser. i think you hit probably dead on what i was asking. sorry im not real good at explaining what im trying to ask.

im too tired to input everything you said right now ill read over it tomorrow and might have more questions and or explain better of what i was trying to ask.

as far as the bowl and nozzle he had a theory he told me in general to do with pumps of all types and fire hoses or something of that sort. im guna have ask him to explain that again, might be a few days before i can get back on that part.

and yes we are green in technical side of jet pumps. when he had his jetboat he was talking to one of eddie hills mechanics for advice. wich was years ago, i think thats were he got most of his information from. Me, im learning most i can off of these boat forums. until a few months ago i never really studied any of this until we started that discussion, motivated me to sit down and figure it out, then i dove off in google search. lol also motivated me to stop buying project cars, boats have less to work on.

 

[gn7]

Bottom line is a Small Block will have to make the same horsepower at the same rpm as a Big Block to spin the same impeller the same rpm. Not too tall of an order if your talking about a 300-400 horsepower stock replacement type of Big Block, but as they say... No replacement for displacement...

You know, this sounds easier to dio than it really is. torque at a given RPM tends to be a product of CID as much as anything. Trying to match a given torque of a BBC at a given RPM with a engine with 100 less cubid inches is not easy task, no matter how mild the BBC is. Mild just mean the torque occurs lower in the RPM, making it that much harder to match with a SBC at the same RPM.

If you have a BBC making 400lbs of torque and you try to meet that with a SBC, thats easy. But at the same RPM, .....thats damn near impossible without forced induction.



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[Budweiser]

Nice answer!

Thanks Tim. Hope you're enjoying your new home.

You know, this sounds easier to dio than it really is. torque at a given RPM tends to be a product of CID as much as anything. Trying to match a given torque of a BBC at a given RPM with a engine with 100 less cubid inches is not easy task, no matter how mild the BBC is. Mild just mean the torque occurs lower in the RPM, making it that much harder to match with a SBC at the same RPM.

If you have a BBC making 400lbs of torque and you try to meet that with a SBC, thats easy. But at the same RPM, .....thats damn near impossible without forced induction.

You are right on the mark, however peak torque isn't really a primary concern in this conversation. For an engine with peak horsepower in the 5000-5500 rpm range it's pretty easy (although not cheep) to build a SBC that produces 400hp. A peanut port mid 1980's smog 454 would come up short in peak HP, but would more than likely as you stated, be the winner in the peak torque department... absolutely.

I can already tell, this is going to turn into a rather lengthy conversation. :happy:

 

[bp298]

You know, this sounds easier to dio than it really is. torque at a given RPM tends to be a product of CID as much as anything. Trying to match a given torque of a BBC at a given RPM with a engine with 100 less cubid inches is not easy task, no matter how mild the BBC is. Mild just mean the torque occurs lower in the RPM, making it that much harder to match with a SBC at the same RPM.

If you have a BBC making 400lbs of torque and you try to meet that with a SBC, thats easy. But at the same RPM, .....thats damn near impossible without forced induction.

nobody, but nobody, ever sizes an impeller based on torque values. it is always about power. the pump is a water brake that absorbs hp. trying to match an impeller to torque values will result in a very slow boat and unhappy boat owner.

bowl work can have an effect on hp absorbed. nozzle work, or nozzle exit diameter changes have never affected hp absorbed, although it will have an effect on the boat's performance.

generally speaking, a big block will make more hp at lower rpm than a small block, unless some type of forced induction is used on the small block that's not on the big block. the only reason that matters is, to keep it simple, the small block will run into a wall trying to climb that hill to get closer to peak hp, way before the big block will.
it would be like those little hydros on saturday trying to get on plane from a dead stop. the pump will be saying "gimme more hp" and the small block will say "ok, just let me spin a little faster", while the pump says "not until you gimme more power"... the pump wins that arguement.

 

[Budweiser]

nobody, but nobody, ever sizes an impeller based on torque values. it is always about power. the pump is a water brake that absorbs hp. trying to match an impeller to torque values will result in a very slow boat and unhappy boat owner.

bowl work can have an effect on hp absorbed. nozzle work, or nozzle exit diameter changes have never affected hp absorbed, although it will have an effect on the boat's performance.

Ummm. I know people have said that a jet pump is like a dyno, and I suppose if your engine turns a certain impeller to a certain rpm you can get a good idea what your engine produces at that specific rpm...

But...

Let's not go too far. A jet pump is a jet pump... and a water brake is a water brake... and a torque converter is a torque converter. (hasn't come up yet, but I'm sure it will soon ) They are all their own thing. Sure, in some ways they are similar, or act similar, or if you understand one you can compare it to another to gain a better understanding. But, in the end they are all different and not the same at all.

The phrase "the pump is a water brake that absorbs hp." is a metaphor. BP, I'm not correcting you. Guys like me and you and others here get it, but a new guy will soak that stuff up like it's gods honest truth and the next thing you know everyone is parroting the same damn phrase.

SQUAWK, a jet jump's a dyno, SQUAWK, a jet pump's a dyno... SQUAWK :bangmyhead: :happy:

The best, easy to understand, explanation as to why impellers are "sized" by horsepower it because they pump water. Want to move more water, gonna have to make more power. Simple as that.

Torque is very important and horsepower can't exist without it... However, in this conversation it will only confuse the subject.