SoCal Jet Boats
Tech Talk => Jet Pumps => Topic started by: hooked on a feelin on September 24, 2015, 07:49:25 PM
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So last season the bowl bearings took a crap, impeller rubbed on the wear ring actually wore through the front of impeller, and impeller touched the top of the bowl as well. Even with all that, the boat ran 68 mph the last run I made with that pump. Had the pump redone, the shop talked me into going from an 'A' to a 'B' saying it would make the boat more responsive and just all around better so I said ok even though I wanted to stay with the 'A'. Now with the new pump, it did pick up about 300 rpm like it should, to about 4900 but lost 4-5 mph up top. Added a 'sportsman' loader grate which brought the rpms back down to about 4600, but no gain whatsoever top end. My question is, is this to be expected when changing the impeller from 'A' to 'B' or is something not right? Also feels kinda lazy out of the hole to but that may be just in my head.
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Sounds about normal. You're moving less water and you engine is likely out of camshaft. Basically over revving.
Need an A or more motor. The difference between the A and the B should be closer to 600 rpm power for power. So you dropped the engine right out of its torque curve.
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
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"More responsive" is not the term I would use to describe the change going to a smaller impeller cut.
Is it a bigger and heavier boat? Do you have a shoe and ride plate? How far below the keel do the loader ramps hang?
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"More responsive" is not the term I would use to describe the change going to a smaller impeller cut.
Is it a bigger and heavier boat? Do you have a shoe and ride plate? How far below the keel do the loader ramps hang?
I was being polite, I have been accused of being a bit "rough".
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
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I was being polite, I have been accused of being a bit "rough".
GT
I'm still trying to learn that one. Not looking promising though.
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I got a DA with some 220 if ya need it....soften up those edges. >:D
(Much love)
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I got a DA with some 220 if ya need it....soften up those edges. >:D
(Much love)
How would you like a triple knuckle throat punch wise guy?
Hahaha.
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
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Lol.....
Wooosaaaah.....
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"More responsive" is not the term I would use to describe the change going to a smaller impeller cut.
Is it a bigger and heavier boat? Do you have a shoe and ride plate? How far below the keel do the loader ramps hang?
Boat is a '79 challenger, 18'. Don't know exact weight but it's not real heavy no. No shoe or ride plate, ramps are 1" to 1.5" below keel maybe.
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Boat is a '79 challenger, 18'. Don't know exact weight but it's not real heavy no. No shoe or ride plate, ramps are 1" to 1.5" below keel maybe.
Well, they better not be.
The scoops should be above the keel line. You will need a straight edge to confirm.
Honestly I think you got some bad advice.
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
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And that loader is not what I would run, and not to add insult to injury, but it should be through bolted with hardened steel bolts, not stainless.
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
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Had a feeling I should just stay with the 'A', thinking I'm going to pick up another one and swap it in there. Really only running that loader because I got it for free and it does keep the rpms down a little bit for cruising. I would rather run the stock grate and keep junk out of the pump.
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And now for a little alternate universe theory:
It is pretty standard to go to a smaller impeller cut with a relatively light 18'.
A heavy boat needs the launch of a larger impeller and takes a hit in out-of-the-hole performance when a smaller cut is installed. However, a smaller impeller will allow the engine RPM higher (assuming it makes power there).
A (relatively) lighter boat like your's won't take such an out-of-the-hole hit in performance like the heavy boat will. So, if the impeller cut and engine power curve complement each other, the boat will ultimately be faster. There will be a loss of out-of-the-hole and for a hot rod (non-race) kind of boat, you will really notice it when pulling skiers.
I wouldn't say you you got burned, I just don't think they looked at the big picture.
Looking at your impeller, I have a couple thoughts. A stock impeller is a pretty crude casting. It is terribly prone to cavitation. The vanes are really thick and don't cut through the water very well. There is a huge knob on the hub, just between the shaft and the root of the vanes which disrupts flow. The radius between the vanes and the hub/shroud cavitate terribly. If you paint the impeller black, you will quickly see the cavitation burn in these areas. This cavitation acts like slipping the clutch while you are driving your car uphill at full-throttle. The RPM increased, but thrust was lost.
When you installed the loader, the water pressure at the inlet eye of the impeller increased, cavitation was reduced, and the RPM was pulled down. This is good, because the impeller is now working harder.
However, the concern is that you didn't pick up speed. With the installation of the loader, drag was increased. There is a balancing act between drag and speed. Too much drag and the boat is slow. Not loading the pump hard enough and the boat is slow.
So, where do you go from here? You will need a 4' straight edge to see how far the loader ramps hang below the keel. Place the straight edge on the fiberglass hull, to project the keel line into the pump opening. Do not try to rotate the straight edge to touch the back of the intake. All you care about is the keel line. Now you can take a measurement to the loader ramps. Just eyeballing it is deceptive.
Because you don't have a shoe, the back of the intake is not doing a whole lot to pick up water. Being a little more aggressive with the depth of the loader ramps can be beneficial. Too aggressive and the loader will shadow the back of the intake all while increasing drag. You can trim the loader ramps to fine tune it to your application. Be sure to resharpen the leading edges.
If you are open to spending more, detailing the front of your impeller will make it bite harder, equalavent to a full impeller cut size simply by reducing cavitation. An inducer (pre-impeller) will also increase the out-of-the-hole performance in much the same way, by increasing the water pressure at the impeller inlet eye, therefore reducing cavitation. The downside of installing an inducer in your boat will be the removal of the pump shaft to machine it for the inducer. That means everything has to come apart.
Hopefully this gives you enough to stew over for a minute. Post up if you have more questions.
Cheers,
Joe
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...it should be through bolted with hardened steel bolts, not stainless.
GT
Really only running that loader because I got it for free and it does keep the rpms down a little bit for cruising. I would rather run the stock grate and keep junk out of the pump.
As GT stated, it should be through-bolted with 5/16-18 bolts with at least the back two having lock nuts installed on the inside. The fasteners should also be replaced frequently.
You should also inspect a loader every trip for cracks and excessive corrosion.
Loaders are under tremendous stress from water pressure. A failure will flip the boat.
And now for some more alternate universe theory:
Installing a rock grate will aggravate your existing cavitation problem. 1.) It is a restriction on the inlet of the pump which deprives the impeller of water. 2.) It is a disturbance to the flow of the water that does find its way into the pump. Now you have pissed off aerated water at the impeller inlet eye compounding the cavitation problem of the crude impeller casting.
In my opinion, keeping rocks and debris out of your pump starts with being a good captain. After you spend all that money rebuilding your pump, the last thing you want to do is do it again.
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As GT stated, it should be through-bolted with 5/16-18 bolts with at least the back two having lock nuts installed on the inside. The fasteners should also be replaced frequently.
Forgot to mention, use a lot of anti-seize on the fasteners!
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When the shop cut the impeller down they also reworked the whole thing, sharpened the leading edge and polished the rough spots from the casting so all that should be good to go. Ilk check how far the ramps are below keel line maybe I can tune them up some.
In your guys opinion should I spend time running this pump up to get back where I want to be, or would I be better off getting a new 'A' impeller, polish it up a bit too get rid of rough casting marks and put it in.
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When the shop cut the impeller down they also reworked the whole thing, sharpened the leading edge and polished the rough spots from the casting so all that should be good to go. Ilk check how far the ramps are below keel line maybe I can tune them up some.
In your guys opinion should I spend time running this pump up to get back where I want to be, or would I be better off getting a new 'A' impeller, polish it up a bit too get rid of rough casting marks and put it in.
I don't mean any disrespect here.
Polishing really does nothing for performance. The only reason we do it is because the customers expect it to look pretty.
The areas where the attention is needed was not touched on that impeller.
You can see for yourself If you paint it with some cheap black spray paint. It doesn't need to be nice and the cheaper the paint, the better. After one day on the water, you will see evidence of cavitation burn in the paint.
As to getting a new A-cut impeller, they are pricey. You will, however, get better fuel economy at cruise along with much better launch. You might lose some RPM at full throttle, but how much time do you really spend running flat out?
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I got a DA with some 220 if ya need it....soften up those edges. >:D
(Much love)
Looks like you are going to have to break out the heavy 9" grinder with the 36-grit dished wheel to knock down these rough edges.
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Looks like you are going to have to break out the heavy 9" grinder with the 36-grit dished wheel to knock down these rough edges.
sorry man....ive gotta be careful with that sanding/grinding business....ive been offered a triple knuckle throat punch (gulp...tug on collar) if i kept it up....
(lol!!! ;D)
(but i do have a nasty 7 incher....sum bitch will put hair on your chest just looking at it)
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(but i do have a nasty 7 incher....sum bitch will put hair on your chest just looking at it)
That just doesn't sound right
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LOL,
shit man, you got me....
could be dirty....
i didnt even realize it......
(seriously, apologies to any that were offended :-\)