There are many factors that affect the load on the drive/propshaft. Boat weight, pitch of the prop, water conditions and how much time the boat is in the water vs air time.

In your case; a light boat, relatively low pitch prop, a small block with lots of hp but not the kind of torque you would have with the same hp with a big block, all lead up to the possibility of an Alpha drive holding up. The plastic hub should hold up.

With the Flo Torque set-up the hub only transfers the torque of the prop shaft to the prop. You can mount the prop without the plastic or solid sleeve in the prop at all but you would be able to rotate the prop on the propshaft. So if the plastic hub were to fail the propshaft would just spin inside the prop. If the propshaft were to break then you lose the prop with it.

Matt

MIRAGE PLUS 25 PITCH
 

we have a labbed 25 mirage plus 475.00 plus shipping and the stainless insert is extra.let me know;)

I would stick with the solid hub on your application. The motor idles pretty tame and goes in and out of gear very smoothly. Keep in mind there is an ignition cut off on Alphas that really helps if they are working properly. The drive will continue to live if you take it easy out of the hole, keep the high speed wave jumping to a minimum, and don't press the NOS button until very close to top end. My concern with the plastic is if it happens to let go while on the NOS. Have you ever heard a motor banging a rev limiter at 6800 RPM on nitrous? I definately can be destructive even though the rev limiter is a soft touch. I think the chances of the drive breaking are lower than the chances of the plastic shearing.

By the way with a 25 standard Mirage we radared Plum Crazy at 80 MPH at 5700 RPM running naturally aspirated shortly before we sold the boat. This motor is really happy between 5800 and 6200 RPM from our testing. My thought is a labbed prop that will allow for peak RPM of 5800 - 5900 RPM could possibly provide 2 MPH or so over the standard Mirage. The 26 Spinelli is very custom as one may guess. Top end is 82 MPH at 6000 RPM. The cruise speed of the Spinelli is not great, but the acceleration is awesome due to the fact it lets the engine rate pretty quickly. We got that Spinelli 5 plus years ago and I think there may be a better prop available now. Just another note the 100 HP NOS shot will add 300 - 400 RPM on top and the 150 HP shot will add 400-600 RPM on top. The motor is solid roller and has a 6800 RPM plug in the limiter.:D It is one hell of a fast bowrider!!!

With out realizing it I ran a plastic insert for most of a season behind a 600hp big block. The insert looked like new.

Houstonprop, how much for the lab finish if I send a prop?

With a 1.47 gear ratio that's a lot of slip, 16%. 80mph@5800rpm with 1.47 gear ratio.

Might want to look at other prop options, if that hasn't been tried already.

Matt

I had a plastic insert in my Carrera Cat without realizing it when the boat was new. It lasted about 20 minutes behind the 632". Went through a couple of waves @3000 and GOODBYE.....;) :rolleyes:

The most fun thing to do with plumb crazy is to go find some mid 20' boats with blown BBC to race. The look on their faces when an open bow, full windshield, small block SMOKES them is priceless...:eek: :cool: :D

Throttleup, the previous owners experimented with a variety of props and, despite the high slip, the boat ran best with the 26p Spinelli and a stock 25p Mirage. What would you suggest?

I would need more information on the boat. If you have a little time give me a call. There are many options. We have quite a few test props that may work for you.

Matt
877 842 6855 toll free