Noisy jet with stainless impeller, and sizing thoughts for altitude

[Colorado Tim]

Howdy all:

I have a older 21' Aluminum Thunder Jet and recently put a new American turbine 9-1/2" bowl and impeller on the Berkley pump housing, and sometimes when idling or at lower RPMs it makes a horrible grumbling/grinding noise (changing RPM's Make the noise go away), in or out of the water. I've taken the pump apart twice and can't find anything wrong, the bearings are all new & I have 25 to 30 thou. between the wear ring and the impeller. I've heard stainless impellers are noisy. Thoughts any one?

Also during a rebuild on the motor I moved from a low altitude of 2,000 feet to a altitude of 5,000 feet and run the boat at altitudes ranging from 5,000 to 8,000 feet. during the first run I discovered the weighted secoindary's open slightly when rapping up then fall back closed so I pinned them open and jetted it so the plugs are a perfect tannish brown, and the boat sounds good and jumps out of the hole and seems to cruise between 35 & 40 MPH,(pulls a skier great) BUT I can't get the RPM's above 3,800 and according to American's turbines impeller selection guide I'm only putting out between 250 to 275 HP, this is very disappointing to me.

My Question is, could that large of an impeller at high altitudes throw the HP charts off, Could I be making more HP Than the charts says, and if I'm happy with the speed does it hurt any thing to run at lower RPM's? Should I go with a samller impeller? Would rapping to higher RPM's make the wieghted sceondary's open with out pinning them open?

My motor is a Gen 4 454 block W/ 427 oval port heads, new 750 Marine Edelbrock carb, new Comp cam .505 in./.515 ex, timing advances to 30-32 dgrees at 2,500

Thanks for any help any one could offer

Tim

[Duane HTP]

You just need to idle it a little faster, and make sure there is plenty of grease on the splines. The heavy impeller is rattling on the shaft/yoke splines from the camshaft duration. If that don't take care of it, check and make sure your shaft splines and yoke splines are in good shape.

[Duane HTP]

Yes, a smaller impeller would definitely help.

[speedboats]

As Duane says, the rattle will be the shaft spline and the universal couple. Pulling the pump apart would have been fruitless unless you tried to balance the impeller. The rattle occurs at different rpm's for different impellers, some at idle (or below) others when you shoot up through 1500rpm, and everywhere in-between. The rattle occurs because of the machining tolerances required to ensure different manufacturers products will mesh together. You can mask this using a heavier grease, particularly one containing teflon. However, if you are super anal you can take the impeller to a machine shop and get them to balance it. As long as the impeller becomes round after about 850rpm you shouldn't hear it...

[sleekcrafter]

A choppy idle and light flywheel, your gonna hear it a lot. The heavyier mass of the impeller chatters the splines at the low rpm's as Duane pointed out