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Discussion Starter #1
how can you measure an impeller to find out what cut it is?

just bought a jet boat, and it came with an extra impeller I wanted to fnd out what it is, the guy I bought it off said it would give me a few more mph, but he didn't say what cut it was,

also the impeller in it is pretty mangled, edges are banged up pretty good,
is that going to make a big difference speed wise?

I got no tach but I'd say I'm turning 4500rpm at WOT,
by going to a cut where I can rev higher is that going to raise my cruise rpm?

thanks, I got a lot to learn, and this things turned into more work then any car I've owned in a hurry, but I think I've found a new outlet, hot cars were getting me in trouble,

here she is, its a beater, but planning on doing a lot of work this winter,
including paint,




http://www.youtube.com/watch?v=CgI90S7vudA
 

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car guy,
The impeller chart is about the same for American Turbine, Berk, Legend etc.



http://www.americanturbine.com/information/impeller_chart_sd309.htm

What else can you tell us about the impeller? Is it aluminum or stainless?

If it is mangled and aluminum it is likely junk. A mangled impeller is not going to do anything good for your performance. Stainless can be worth the cost of repair.

If you go to a cut you can rev higher, you will increase your cruise RPM also. Reving higher may or may not increase your top speed, it depends on where the power band is for your engine. If you are currently running below your power band, increasing the RPM so you run get into your power band can increase your top speed.

I hope this helps.

Doug
 

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I got no tach but I'd say I'm turning 4500rpm at WOT,
Hey Car Guy,
First thing you need to do is get a working tach. You will be chasing your own tail if you try adjusting the boat by the "seat of the pants" method.

What makes you think the engine has "more in it"? You really need to know what parts are in the engine, or maybe do a couple dyno pulls to make that call. To start with, I don't see a real high performance engine, due to the fact that it still is running the log style manifolds.

See if you can do some research and find out what compression ratio, the cam specs, cast or forged pistons, etc.

You can certainly play with impeller size, and other setup changes and make some gains. I am only trying to say that it is easier and more effective if you know what you are working with to begin with.

Post a picture of that impellor. If it is aluminum and "mangled" it is probably junk. (all depends on your definition of "mangled") If it is just nicked, you could probably clean it up and it might work okay.

Good Luck
Doug
 

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Glendale Arizona
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2,368 Posts
One thing I can see in the video is that the boat rides really flat and wet. You've got spray
coming off all the way up to the passenger seating area. On a good riding semi-V you'll only
have spray coming off the last foot or so of the sides (some even less than that).

If you have a split bowl pump you might try putting some up wedge to it. Sometimes that'll
help loosen em up. Better yet a droop snoot if you can find one to try (without having to buy).

More wetted surface = slower speeds.

Doug's (real McCoy) suggestions are good ones. I'd say make sure the pump is squared away
first, then you can go after more power, ride setup etc. A tach and gps are pretty much a
necessity when tuning. Like Doug said, seat o the pants just doesn't work. I also find that having a
friend video the ride at speed helps to figure out if any changes that were made help out with the way
the boat is riding.

Here are a couple videos of some 100+ mph semi-v's. The quality of the video isn't
that great, but check the sides of the boat and where the spray breaks off the sides.

RCB vs. Woods

RCB vs. Woods II

Or here is a still of one of those boats. The sides aren't even touching the water. Only
the very back and bottom of the hull. Granted these boats have over 700 hp, but you
can definitely improve on your ride (dry the boat out) with significantly less hp.

 

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Discussion Starter #6
Hey Car Guy,
First thing you need to do is get a working tach. You will be chasing your own tail if you try adjusting the boat by the "seat of the pants" method.

What makes you think the engine has "more in it"? You really need to know what parts are in the engine, or maybe do a couple dyno pulls to make that call. To start with, I don't see a real high performance engine, due to the fact that it still is running the log style manifolds.

See if you can do some research and find out what compression ratio, the cam specs, cast or forged pistons, etc.

You can certainly play with impeller size, and other setup changes and make some gains. I am only trying to say that it is easier and more effective if you know what you are working with to begin with.

Post a picture of that impellor. If it is aluminum and "mangled" it is probably junk. (all depends on your definition of "mangled") If it is just nicked, you could probably clean it up and it might work okay.

Good Luck
Doug

not sure on the specs, its got some good lope at idle, but not sure if thats normal for marine and a carbed big block, I'm more a a fuel injected small block kind of guy, and they got to run pretty smooth to idle
plan on getting a tach right away, just got a lot of other stuff to do on it,
including making the trailer more road worthy, and my V8 s10 is heating up like crazy pulling the thing,

the impeller is pretty banged up some of the nicks are 1/4" or more deep

say I knew my cut, and had a working tach is there anyway to guess hp?
buddy I bough it off is a family friend and a big time bracket racer(has a couple low 10 second cars)
he siad the engine would make 400-450hp,

thanks for the help,

looks like I got a big learning curve ahead of me, but I want to get this thing tuned and running well before I start building a new engine
still a blast to drive this thing I can spray my buddys in there supras, malibus and out boards, and they can't do anything about it, lol
 

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Discussion Starter #7
One thing I can see in the video is that the boat rides really flat and wet. You've got spray
coming off all the way up to the passenger seating area. On a good riding semi-V you'll only
have spray coming off the last foot or so of the sides (some even less than that).

If you have a split bowl pump you might try putting some up wedge to it. Sometimes that'll
help loosen em up. Better yet a droop snoot if you can find one to try (without having to buy).

More wetted surface = slower speeds.

Doug's (real McCoy) suggestions are good ones. I'd say make sure the pump is squared away
first, then you can go after more power, ride setup etc. A tach and gps are pretty much a
necessity when tuning. Like Doug said, seat o the pants just doesn't work. I also find that having a
friend video the ride at speed helps to figure out if any changes that were made help out with the way
the boat is riding.

Here are a couple videos of some 100+ mph semi-v's. The quality of the video isn't
that great, but check the sides of the boat and where the spray breaks off the sides.

RCB vs. Woods

RCB vs. Woods II

Or here is a still of one of those boats. The sides aren't even touching the water. Only
the very back and bottom of the hull. Granted these boats have over 700 hp, but you
can definitely improve on your ride (dry the boat out) with significantly less hp.
I though it was riding low compared to a lot of the pics and vids I've seen,

heres a pic of my jet, is it split bowl?



I seen those wedges online, they were like less then $50 or something,
I'll probably grab 1 if you think it'll help, I'll look arounfd locally if somebody got a droop snout I can get for cheap or borrow
 

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Discussion Starter #9
so the wedge goes between the big bowl part and where the jetovator tilt bolts on, just behind the grease nipples?

that access hole on the back of your is inside my hull
 

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Glendale Arizona
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so the wedge goes between the big bowl part and where the jetovator tilt bolts on, just behind the grease nipples?

that access hole on the back of your is inside my hull
Yes that's where the wedge goes. I'd probably try a 3 or 4 degree and wedge it up (thick side to the bottom). It usually helps to get the bow up and bit. It's a good starting point for ride tuning as it doesn't cost a lot of money and it's a tuning tool that you can use in the future when you make other/more changes. Pretty much everybody runs a wedge Whether it be up, or down. Even the guys with lots of pump work and ride tuning. I have four different ones in varying thicknesses 1, 2, 3, and 4 degree.

Your hand hole is in the typical stock location.

Like H2MOFO said, a lot of us run a setback pump which is why the hand hole is out of the boat.
 

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Hey Car Guy,
From the picture I can see that you have a JetoVator, does it work? If it works, have you tried raising it up to see if it will lift the front of the boat? Edit - I should read before posting - I assume from the post above that it does work.



Oh, if you know the impellor cut and feel the pump tolerances are in spec you can get a fair idea how much HP you are making from an impeller chart. I don't have a link right now, maybe I can locate one later. Just read the RPM on the bottom, follow the line up to the curve for your impellor and then follow the line to the left to see what HP will turn that RPM. It is not exact, but gives an idea.



Have fun.
Doug
 

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Wow that was a great day, almost nobody else on the water and not a ripple. The best skiing conditions I can remember.

I could barely lift my arms onto the conference table at the meeting the next day. By far the best business trip I have ever had.

Doug
 

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jetboataholic
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Ok, to determine the cut of your extra impeller, you need to get some 12" calipers and measure the top and bottom diameter of the outlet side of the impeller vanes. There is a chart for determining what cut impeller it is, but we need to know what brand impeller it is to be able to determine that because the different manufacturers have different dimensions for the same letter cut. Here's a link to a thread I started awhile back that has the Dominator impeller chart on it, maybe some of the other guys will chime in with the other manufacturers charts.
IMPELLERS!

Good luck.:D

:)hand
 

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Discussion Starter #19
I actually looked at it, it has an "A" stamped on it,

so I'm going to guess and say its an "A" cut,

need to do more work to this thing but I keep breaking it,
all my spare time is spent keeping it running, last week a rope managed its way into the U joints and tore the guard off and ripped out all the wiring,
week before it was a shredded rage in the bilge pumps,
finally learned to quit putting stuff in the back,

and the $400 fuel bills every weekend aren't helping me buy any new stuff for it,

turning into an expensive hobby, might have to sell some other toys to help fund :D
 
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