If the pump is worn some, a refresh on the pump may loose 3-500 rpm, then cut the impeller for the rpm you want- AB or B.
I lost 4-500 rpm with a fresh pump, had the impeller detailed, and gained mph at a lower rpm (kept same SS impeller)
But thats on my junk

Daniel

A tight, loaded, A impeller should turn about 5000-5200rpm, so either your pump is a little looser, it's not loading right, or you're making more power than you think. Also if your engine really does want more RPM, you will definetly see more MPH cutting your Impeller, anywhere from 2mph-10mph depending on your whole setup. And if you do cut the impeller you won't have any noticeable loss of cruising speed for MPG.... these things suck gas no matter what you do, but you won't be able to tell if you're getting worse mileage from the impeller cut. If you have a 20' or bigger boat you might notice, but it'll be minimal

A tight, loaded, A impeller should turn about 5000-5200rpm, so either your pump is a little looser, it's not loading right, or you're making more power than you think. Also if your engine really does want more RPM, you will definetly see more MPH cutting your Impeller, anywhere from 2mph-10mph depending on your whole setup. And if you do cut the impeller you won't have any noticeable loss of cruising speed for MPG.... these things suck gas no matter what you do, but you won't be able to tell if you're getting worse mileage from the impeller cut. If you have a 20' or bigger boat you might notice, but it'll be minimal

Hate to disagree with anyone outright, but this statement is not necessarily true. Way too many variables......

May be true with your particular deal, but this would not be true for many applications out there...

That's why I said such a broad range, depending on alot of factors. If you motor actually does want more RPM, you'll see at least a minimal gain. Any application out there, if the impeller is cut to where the motor wants to shine, wouldn't it pick up performance? What's your take on it GT.

Tony, sorry, my lame ass has not been on here much lately to respond.

The OP stated he is already running at 5300+ RPM. If he were to cut the impeller to gain RPM, I am afraid the volumetric efficiency on the pump would drop more than the added RPM would be able to make up (in short, a step backward). Then again going with a AA the motor would be overloaded and may be somewhat lethargic on the top. (again a step backward).

There is absolutely no formula that I have ever heard of (that works) to calculate speed gains based on added HP to the water on a jet.

The best "bang for the buck" on this set up right now I believe would be nozzle tuning and potentially playing around with a loader, these are reversible modifications and if done one at a time can be gaged to determine what works and what don't.

If the peak torque is in the 4500 RPM range, all the parts going along with it have to be set up to keep the top RPM figured for not too much over that, as an example I would not use large tubed headers nor would I try to use a Dominator carburetor. It is very easy to buy into the more is better ideology as far as RPM, but you don't have to move too far to fall off the shelf. IMHO a "B" impeller will kill performance. And putting an AA in it will gain some hole shot performance and maybe a few percent more mileage, but top speed may drop off by an unreasonable amount, you want mileage?, get a prop driven boat..Or install a three stage Hamilton pump..

BTW, to the OP, there is a pretty good chance it will never get to the RPM of peak HP, because the torque numbers will fall off like housing prices....

Your setup sounds pretty close and you are at the tuning stage at this point, unfortunately the tuning part is the most frustrating. 

Good luck, Sounds like a killer project 

GT

Tony, sorry, my lame ass has not been on here much lately to respond.

The OP stated he is already running at 5300+ RPM. If he were to cut the impeller to gain RPM, I am afraid the volumetric efficiency on the pump would drop more than the added RPM would be able to make up (in short, a step backward). Then again going with a AA the motor would be overloaded and may be somewhat lethargic on the top. (again a step backward).

There is absolutely no formula that I have ever heard of (that works) to calculate speed gains based on added HP to the water on a jet.

The best "bang for the buck" on this set up right now I believe would be nozzle tuning and potentially playing around with a loader, these are reversible modifications and if done one at a time can be gaged to determine what works and what don't.

If the peak torque is in the 4500 RPM range, all the parts going along with it have to be set up to keep the top RPM figured for not too much over that, as an example I would not use large tubed headers nor would I try to use a Dominator carburetor. It is very easy to buy into the more is better ideology as far as RPM, but you don't have to move too far to fall off the shelf. IMHO a "B" impeller will kill performance. And putting an AA in it will gain some hole shot performance and maybe a few percent more mileage, but top speed may drop off by an unreasonable amount, you want mileage?, get a prop driven boat..Or install a three stage Hamilton pump..

BTW, to the OP, there is a pretty good chance it will never get to the RPM of peak HP, because the torque numbers will fall off like housing prices....

Your setup sounds pretty close and you are at the tuning stage at this point, unfortunately the tuning part is the most frustrating. 

Good luck, Sounds like a killer project 

GT

I was just going off of my experiences, so far I haven't seen a drop in mph from going with a small cut, but I have seen it break even. I've also written down different speeds at different RPM's from 2 different boats, and then cutting the same impeller and trying it again, here are a few results.

1980 Eliminator, 18', 550hp mild BBF.
RPM     A imp        B- Imp
3500  23.2          20.6
4500   58.9           57.6
5400   78.8           78.5
5600    N/A            79.0


And here was my boat, Hondo Pantera, at the time 402CI BBC, 400-450hp
RPM     A imp       B Imp
4000    42.0        40.6
4500    56.5         56.2
4800    68.8         68.0
5000    N/A           72.2

Granted I now have a 460CI BBC, around 550hp, turning the B Impeller 5600 RPM at 82.2mph. Granted I also picked up 3mph going from an 850dp to a 1050  And I just tried some newer headers, they're 2 1/4" primaries, and it only ran 5200rpm with those headers, hoping to get that performance back switching back t my 2 1/2" Bassetts, otherwise I'm going to have to find the problem somewhere else 

Also, talking with a few of the jet boat racers at NJBA races I don't think any of the faster N/A guys run just a straight "A" impeller. Seemed like the most common were B/C's because of how hard they could RPM the motor to make it launch. Also I believe Bonneville76's boat went from 72mph to 82mph going from an A cut to a C cut, Ron could clarify that if he's reading  I will hopefully being trying a C impeller in my boat once the pump is back apart again.

I'm just saying, if his motor actually does want more RPM like he says, I can only see it gaining performance everywhere under acceleration if you can make the motor sit in it's happy RPM range.... but if it doesn't want more RPM, he will lose performance and cruising efficiency going with a smaller cut.

I was just going off of my experiences, so far I haven't seen a drop in mph from going with a small cut, but I have seen it break even. I've also written down different speeds at different RPM's from 2 different boats, and then cutting the same impeller and trying it again, here are a few results.

1980 Eliminator, 18', 550hp mild BBF.
RPM     A imp        B- Imp
3500  23.2          20.6
4500   58.9           57.6
5400   78.8           78.5
5600    N/A            79.0


And here was my boat, Hondo Pantera, at the time 402CI BBC, 400-450hp
RPM     A imp       B Imp
4000    42.0        40.6
4500    56.5         56.2
4800    68.8         68.0
5000    N/A           72.2

Granted I now have a 460CI BBC, around 550hp, turning the B Impeller 5600 RPM at 82.2mph. Granted I also picked up 3mph going from an 850dp to a 1050  And I just tried some newer headers, they're 2 1/4" primaries, and it only ran 5200rpm with those headers, hoping to get that performance back switching back t my 2 1/2" Bassetts, otherwise I'm going to have to find the problem somewhere else 

Also, talking with a few of the jet boat racers at NJBA races I don't think any of the faster N/A guys run just a straight "A" impeller. Seemed like the most common were B/C's because of how hard they could RPM the motor to make it launch. Also I believe Bonneville76's boat went from 72mph to 82mph going from an A cut to a C cut, Ron could clarify that if he's reading  I will hopefully being trying a C impeller in my boat once the pump is back apart again.

I'm just saying, if his motor actually does want more RPM like he says, I can only see it gaining performance everywhere under acceleration if you can make the motor sit in it's happy RPM range.... but if it doesn't want more RPM, he will lose performance and cruising efficiency going with a smaller cut.

Hey pdub...

Are you saying in the Eliminator example that the added .2MPH was worth the 200RPM? I'm thinking not, being as the OP mentioned his concerns about losing MPG...  In that example, I would LOVE to see what a nozzle reducer would do with the A impeller....

Also, in the Hondo example, you are turning nowhere near the 5300+ that the OP is saying he is already at....the volumetric efficiency really falls off at above 5200 on a factory cast impeller....Loading needs to be spot on running them much higher than that.

As for the drag race guys, different animal all together, somewhat like comparing a Winged Sprint car to a four cylinder road racer.
 

Digging the information though, thank you for taking the time.   


BTW, I could have remembered it wrong, but think there was a motor change in there somewhere between the 72 MPH vs. the 82 MPH. Never seen an impeller change make more than about a 3 MPH change.

GT

Hey pdub...

Are you saying in the Eliminator example that the added .2MPH was worth the 200RPM? I'm thinking not, being as the OP mentioned his concerns about losing MPG...  In that example, I would LOVE to see what a nozzle reducer would do with the A impeller....

Also, in the Hondo example, you are turning nowhere near the 5300+ that the OP is saying he is already at....the volumetric efficiency really falls off at above 5200 on a factory cast impeller....Loading needs to be spot on running them much higher than that.

As for the drag race guys, different animal all together, somewhat like comparing a Winged Sprint car to a four cylinder road racer.
 

Digging the information though, thank you for taking the time.   


BTW, I could have remembered it wrong, but think there was a motor change in there somewhere between the 72 MPH vs. the 82 MPH. Never seen an impeller change make more than about a 3 MPH change.

GT

I think you're right GT... I think he went from the 427 to over 500ci. 

There might have been a couple other changes, but it was still the 427ci motor. I think he was running around 4800rpm at Puddingstone with the A impeller to 6000rpm or so with the C impeller in Parker? I'll shoot him a PM. The bigger motor he was going alot faster...

And you're def right, we ended up going back to an A in that Eliminator, but that was the best way to find out. His Ford didn't have as much Cam/Head as my Chevy did, and obviously didn't need to turn any more RPM. Also when I had gone from 72mph to 82mph it was with a motor change from 402ci to 460ci. According to my Cam card my Peak RPM should be 6000rpm.... but I decided to not run that small of a cut, and just to squeeze some laughing gas to get a little more RPM  But I would like to try a C impeller later and see if I gain or lose speed. That's really the best way to know, is just to try it out. 

I really want to run some nos and see how it likes it, what size bottle to u have I am already running water/ meth  kit

Really never been too much of a NOS fan... too short of a burst of power for me, reminiscent of the Indy car Push to Pass...

Your bottle needs to be enormous and have a bottle heater on hand.

GT

There might have been a couple other changes, but it was still the 427ci motor. I think he was running around 4800rpm at Puddingstone with the A impeller to 6000rpm or so with the C impeller in Parker? I'll shoot him a PM. The bigger motor he was going alot faster...

And you're def right, we ended up going back to an A in that Eliminator, but that was the best way to find out. His Ford didn't have as much Cam/Head as my Chevy did, and obviously didn't need to turn any more RPM. Also when I had gone from 72mph to 82mph it was with a motor change from 402ci to 460ci. According to my Cam card my Peak RPM should be 6000rpm.... but I decided to not run that small of a cut, and just to squeeze some laughing gas to get a little more RPM  But I would like to try a C impeller later and see if I gain or lose speed. That's really the best way to know, is just to try it out.

No truer words have ever been written/spoken...