Compared to other racing venues I've been involved in, why not just make the boat weight have a minimum with driver, and not restrict the engine size? Would cover alot more than just aluminum blocks. Possibly could cover future Kevlar boats, ultra light unsafe boats, etc. Just hook up a scale, everyone has to weigh this, this is the engine size you're allowed, now go for it. Seems simpler to me, just my 2 cents. 

Who was claiming they had a large engine? I've been out of the loop.

I put mine right where the center of gravity is on my boat. There was a long, detailed thread from circle racers about it on here, and that's what I took away from the subject. I will try to find it. There's several members on here that have tried different placements in their boats, maybe they'll chime in as well.

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. 

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.

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

In my learning curve of jet boats I learned something that I wanted to share so that other newbies dont make the same mistake. I changed up my new to me boat a little because on paper and in reading it made sense about having too much water pressure in my block. Per the internet I had to have 2 -10 or 5/8's return lines off my block because if I didnt I'd have way too much pressure and possible push out gaskets and I needed a ball valve to control water to my OT Bassett headers. Well I made the changes and went out this past weekend to see how it works. At first I had a gauge on the manifold that read up to 100psi because I didnt want to over peg the gauge and break it-lol what a joke. I couldnt really get a good reading Saturday because of some factors but I didnt really see the gauge move so on Sunday at South Cove the water was like glass and I got a chance to really hammer down, oh and by the way I installed a 15 psi gauge. Under full throttle I only saw 7 psi of pressure and at idle maybe 1-2 psi. So the whole over pressurization of the block article was bull on my stockish big block. What I should of done first was installed the gauge and seen what was going on and installed a ball valve going to my spring loaded t valve for the headers. Now that I have a new hole in the back of my boat for a dump I dont need I will just add another valve to shut it off or possible insert a restrictor into the hose.
After researching this again, here, yesterday, someone already pointed this out I guess if have a high rpm engine or upgraded jet you dont need this, maybe But even though its my fault for not looking here first thanks to everyone that has posted on this subject earlier.

Just because you didn't build alot of pressure doesn't mean you shouldn't do things the right way. That's the best way to set up a boat with headers. When you get some horsepower, and started messing with the pump your water setup will already work. Even if you're only pumping 7psi through the line, you're still moving alot more water than a normal car setup when you consider the volume you're moving. If you're not seeing any water temperature rise, I don't see why you would want to restrict the water?

Speed in the straights is good, but you need to be able to hold your lane in the turns.

Who did hold their lanes this weekend. It's not like LB has alot of room in the turns, especially when you're turning with throttle...

Lived there for 5-6 years, moved away in October to San Diego.... not enough money. There's only 200,000 people in total of all of Mohave County, and the average income is low enough to not make any real economy

Cool looking hull but....

Very cramped interior wise, Crewchief actually has a little extra room from the regular Hondo Pantera. Pretty much a 3 seater, 4 when cramped. Also they don't turn very well from the factory, I have a very large turn fin on mine now to make it turn. Also you would NEED splash guard on the back, they sit very low in the water and are easily sunk by wakes due to being so low and skinny in the back.

But in general I think they're a very cool looking hull, love the body lines. Can be made to go decent speed with work, fastest I've had mine is 82mph with 550hp, but not done playing with setup. And the price is very good on that one.

Pdub

Crewchief's and mine

I should be at Wash 10 or so 

Had a blast. Beautiful weather and boats. Glad to see everyone out there, and meeting a bunch of new people. Just got settled in here at Lakeside, it's warmer than Laughlin! Maybe hit up El Cap a couple times before it's freezing

I'm pretty sure the Cove is if you launch at Lazy Harry's, at the first right hand turn there's a no wake Cove on the left if you look at Brad's picture. Very nice beach about 100' long, but also hidden from view due to toolies.

I think Rio Lomas beach is the biggest/most visible beach for everyone. It's half way between Rotary Park and the Avi on Arizona side. People familiar with the area know it's near Target in BHC. That's where most likely we'll be so I can attempt to see everyone cruising around. Be there at 10am if anyone wants to join. It's a great mid way spot from the Avi to the Casinos.