565edge

What is the height difference between the blackhawk and bravo?How much higher is the prop than on a bravo?I have a 22' daytona with a blackhawk bottom that im putting a bravo in.Im going with a imco sc drive and want to know if i should go with a 2" or 3" shortened drive?Do any of you have experience with this?One guy says run a cleaver and others say run a roundear prop.I need help.Let me know.Thanks in advance:Allen.

Cord

iTrader: (2)

I responeded to your questions on the HB site. You will want at least a 2" shortie. The 3" shortened drive is dramatically more expensive, but even then you'll still be deeper than the blackhawk. At some point you'll get into planing issues, but I don't know when. I do know that on my boat, a cleaver isn't capable of carrying the bow for a decent airpack. I do have experience with a round ear Mirage. I used it when I got into some hazardous water. The prop would slip badly when planing and never even got close to hooking up. Slippage was 50%+. Without a extension box you will never get on plane. You could be cruising at 25mph and nail the throttle. The revs would instantly bang the rev limiter and the boat would gain maybe 20mph. There has been a lot of talk of the 5 blade props. I havn't had a chance to try any of them, but they do look promising. My choice would be between a 5 blade merc or hydro or the 4 blade Bravo 1. The 5 blades should help the hydro to plane as I'm not sure if you could get a 4 blade on plane. Of course, the bravo is proably the best planing prop on the market.

Assuming a 415hp 502 and 1.5 bravo drive...I'm thinking a 28" Bravo 1 would be about right. Maybe a 26".

Make a point of talking to "Airpacker" on this board. He too has a daytona and went from a Bravo to a blackhawk. I believe he saw 8mph gain with the BH.

565edge

Thank you for the response.The motor is a 11:1 comp 565" chevy with a .730 lift solid roller cam.Hope that helps.Thanks again.

Airpacker

The bh drive is 5 inches shorter than a bravo drive but that isn't really important here. the two are designed to work differently, a bravo cannot be run at the same height. You really need to measure from the bottom of your sponsons to the centerline of the engine and pick the drive according to that measurement to achieve a propshaft centerline at or just slightly above the sponson bottom. Eliminator seems to play around with x dimension so i dont know what height your package is mounted at. Measure twice,order once

Cord is correct, i picked up 8 mph going to the bh drive but it does have limitations( docking,low speed handling,horse power compatability,parts availability etc)

aTX427

You probably should check with Eliminator on the x-dim. They offered a 22 with a blackhawk that ran north of 90 with a 502efi. Your biggest limitation will be the torque your motor is putting out. The next will be props/gear ratios. 1.36 with 31" props is the biggest you can go unless you have custom props made. There is a prop shop that mercruiser used in Oklahoma for custom applications called Hoss Props. I believe he still has blanks that can be custom made to order. Alternately, you could go with a 2-speed transmission inside of an extension box. If you look hard enough, there is an application engineer still at mercruiser in Stillwater who was involved in the joint project with Eliminator. I can't find his name, but he was very willing to share information with me when I experimented with the drives. It was good for almost 10 mph with non-lab props. Mid range was awsome as well. I was expecting ~115 out of my 25 with a hp500efi whipple package. We ran 106 with 1.36 gears and 31" props and it hit my 5850 rev limiter as fast as I could push the throttle wide open before I could even hit the trim. With the bravo, we are only good for 103.

Airpacker, glad to hear you got that project complete.