unbroken

I have a 2002 Baja 302 with a pair of built 383's putting out 352 HP at the prop shafts. I have a set of Rev 4 23's that run well, but are costing me a little top end, about 2 MPH. My boat has Bravo 1's, with ratio's of 1.5. I also have a set of Mirage Plus 23's that give me a GPS of 68.5 at 5000-5100 rpm's. Its 95 degrees here, and its still running well, however I really would like to see 70 in the heat. She's heavy, about 7800#'s and I am more than pleased with my performance, but again, I am sooo close to 70. Would I be better to lab the mirages or the Rev 4's? The mirages tend to blow out, not easily, but I have to baby it a little more. If I labbed the 3 blades and changed the pitch to 24, would that help? Brent, Julie?????????? HELP!

throttleup

At what RPM is your peak HP produced?
What drive and gear ratio?

Julie

unbroken

Bravo one drives, 1.5 ratio

from 5200-5400 there is 1.5 HP difference, so anywhere in there should be good I would think.

HiPerf2000

iTrader: (2)

will 24p hydro QIV's work for you ??? I have a set for sale.

throttleup

Well I have calculated your slip at 6% with the 3B Mirage Plus...which I don't have to tell you is very very unlikely! I would verify all recording devices and baseline again. If they all hold true I would recommend that you don't touch / modify that propeller. It just isn't gonna get any better than 6% on a Vee Bottom, non-stepped hull.

Julie

unbroken

Julie, I was looking at that too, and thought that was off, but I hooked up a tach to verify the rpm's not long ago. The GPS is brand new, and I verified it with my airplanes gps Ground speed readout, what else could be off? The drives say 1.5 on them. I switched over to the 4 blades and will be taking it to the lake today. They are the rev 4's. WHat type of slip should I expect from that one?

throttleup

The range of a 4B, on a Vee Bottom is 10-14%.

Julie

bbladesprops

Not to disagree with you Julie but we have seen many true V's under 10%.. However, higher slips on true V's often produce better top speeds. Slip % can be over rated. If the 3 blade runs 6%, the 4 blade will be close too. It could actually be higher than the 3 blade for various reasons

I think what Julie may have meant was, anywhere under 15% is acceptable on a hull such as your's.

My thoughts are, Lab the Mirage Plus props. You have rpm room to grow and 1.5 mph is definately in reach.

unbroken

Thanks Brent, remember, its 95+ degrees here too. I think when it cools down, she will scream. LOL

unbroken

I switched to the Rev 4 23's for the weekend, and filled it with 150 gallons of fuel, and still ran 65.1, thats an extra 700 pounds of fuel over what I normally carry. The boat still turned 5000 rpm's, and it was 95 degrees, and very humid. I used the prop slip calculator, and it said 11% for those props, so at a lower weight, I would think 67 MPH would be attainable. How is my crappy old BAJA's props running so efficient? Does that mean I don't have much to gain from labbing?