Impeller Question A or B

[cave]

Thanks LVB. I asked this because before I started this advrnture into the pump I was looking for a jet boat cam. I wasnt sure what grind I wanted to get so even tho this cuts into that whole deal, I woundered if a different impeller would gain me anything. Looks like I'll stick with the "A". I dont have the HP to to make it matter.

[Shark In The Pond]

Cave, impeller sizing is based on power not torque. If you want best top speed and on-plane acceleration, size to power not torque. The key is, you need to know your engine's power curve to decide if smaller is a good trade-off.
Typically, impeller sizing becomes more critical as power goes up. A stock motor pulling an "A" to 4200 is not much power and I don't think downsizing to a "B" will gain you much. Even with a 900 hp engine where one cut size may get 40-50 hp if off-peak power, only 4% increase in speed. In your case that may be 1 mph assuming your engine's way off-peak power at 4200 rpm.
That said, I don't don't think going from an A to a B will be a problem with pulling a skier. At least not from my experience. I've pulled many a skier with a "B" and at least one complained about having his arms pulled out of the sockets. An exageration on his part I'm sure, because I ease-in the throttle and pull smooth but still, why do some say a "B" won't pull? Is there anyone else out there that can or can't pull a skier with a "B"? I weigh about 215+ lbs and on a single ski pull up just fine on a "B" Just wondering.
jer
I did not understand also about pulling up a skier with a B being a problem I run a B in mine and never had a problem . I thought I had a little power untill Jer told me about my power being about 385hp

[Mohavekid]

I ran a "B" in my Challenger. I had no problem pulling a heavy skier, I weigh about 225.
My motor was pushing close to 600 HP and pulled the "B" in a tight pump to 5800 RPM.

[TexasJet]

LVjetboy, I have a B impeller in my 19' Baja. I have pulled 2 adults up on slalom skis with no problem. I just put the Place Diverter in the down position and roll the throttle to wide open for a few seconds.

[Jungle Boy]

You should check your thrust bearing real close while you are repairing your pump. To have that much damage to the leading edge of your impeller, it tells me that you may have a damaged bearing as well. If it goes, then your impeller will move forward and rub up against the wear ring. I had the same type of damage once and it was caused by a bad thrust bearing. Failing to replace it will cause the same damage to your new parts and you'll be a sad man. :cry:

[cave]

yea its bad,
http://members.cox.net/jetboater454/thrust_bearing.jpg
this is whats left. Oh I got some cool steel marbles out of it.

[Marlin455]

Cave- You might wanna pull the pan on the motor and check the main thrust bearing- If your pump ate the impeller like that, all that thrust was trying to push your crankshaft out the front!! It can do some serious engine damage !
Just my $.02--- Stan

[cave]

The motor is out and I checked it out. Just have to replace the rear main seal.
That was the easy part.

[Jungle Boy]

Holly Shiete, That's some fugked up bearing. Us river boat guys generally change them out each winter. It might be a little often, but it's a lot easier than motor repairs.

[cyclone]

I did not understand also about pulling up a skier with a B being a problem I run a B in mine and never had a problem . I thought I had a little power untill Jer told me about my power being about 385hp
Trying to pull a skier out of the water with a b-cut impeller is generally not a problem unless you are are in a larger, heavier 21-foot and up boat. Larger boats will usually have a weak holeshot to begin with and switching to a smaller impeller will only worsen the condition. This also becomes true in high-horsepower applications where the engine will spin a smaller impeller faster than the intake can deliver the water to it. The result is cavitation and and weak holeshot. I dont believe this is the case with Cave's boat though. In his boat, I think going to an A/B-cut would be a better choice. It will allow the engine to spin a little more rpm, getting it closer to peak rpm, while still keeping a decent holeshot and low cruising rpm. Going from an A-cut to a B-cut impeller will also do the same, but the cruising rpm will be much higher and the holeshot, a bit weaker.