Which Impeller With These Dyno Numbers

[wmitchell]

What would you experts recommend for an impeller choice with these hp numbers and a big heavy boat??

[Bahner tunnel]

What would you experts recommend for an impeller choice with these hp numbers and a big heavy boat??
I'm thinking an "AB" .

[Nucking futs]

I'm thinking an "AB" .
Agreed. I ran an Aggressor BC (berk AB) in my 20 with 600 HP and it turned 5900 rpm I went back to an A because it lacked in the whole shot and didnt like cruising at 45-4800 rpm

[wmitchell]

Hey Fut's how bad was the whole shot?... I hate when it takes a little to long to get going in a cruiser and you feel like you're sucking a hole in the water before the pump starts to completely load. Nothing worse than making a ton of noise and not going anywhere fast!

[Nucking futs]

Actually it wasnt that bad. It moved out real good for a heavy boat, but nothing like it does now with the A in there. I could live with the whole shot issues, it was the cruising @ way high RPM's and burning off all my fuel cruising. I would do the WOT passes and all, but I Get such better milage with the A. I was running a Tram too, but that came off and I went back to an 850. I finally came to the conclusion after a summer of trying to get every last bit of speed out of it that shes just a cruiser and not a race boat. Sure its nice to have a fast "Bigger" boat and all, "but It is what it is"....:D
If you have an A in it now, run it and see how you like it.

[Gearhead]

Warren,
A couple of things. Just quickly looking at your corrected numbers I agree that the A to A/B is going to be close. Do you have the uncorrected dyno numbers? The uncorrected power is all you actually have on a given day and the pump will let you know it. If you have those numbers we could better recomend your needed impeller size.
Also, those BSFC numbers look a little low. Depending on the calibration of the fuel flow sensors on the dyno, this could indicate a lean condition on a single plane intake and design of the engine. I would take a good look at the spark plugs after a hard run to see how they read. A jetboat, especially lower compression ones or ones running pump gas, may respond favorably to a slightly richer jetting. You can try this by reading the plugs, changing the jets and watching the tach.
I hope this helps.
Gear

[wmitchell]

Hey thanks to all of you that does help... I checked the plugs several times during the dyno session and they were on the light side of tan. Will check more when I'm in the water... this was a ZZ502 and the compression is still 9.6/1