Katanna

iTrader: (1)

My magnum was a similar hull but lighter-high rev 280 small blocks would turn 5k with 23s. Back in the days of working at a dealer rigging wellcrafts, all the scarab panthers received 23s with the 454 mag and 21s with the 330s. That was through bravo dirves. You are spinning small blocks through transmissions and trs drives. Bullet proof package but not efficient. If memory serves me you loose about 18 percent of your power going though the trans and trs. Your WOT target should be 4700 with light load. This would give you your most efficient cruise speed at 3400. 21 Mirage should put you there.

TruxtonFox

Is there anything to be gained by spinning the motors at a higher RPM than 4700 under load? Obviously the inherent risk of blowing something up, but if the blocks were built to handle say 6000 RPM for sustained runs, is it advantageous or just a waste of fuel.

I'm sure these questions seem rudimentary, but I do appreciate the time yall are taking to answer.

CDShack

Generally HP/torque figures rise as RPMs rise. If you can let them spin a little faster, you get into more HP/torque. The hope is the gain in HPTQ will allow the prop to spin faster than the pitch difference, and you gain speed and efficiency, along with acceleration and better "boatability". Example: say you drop two pitches and mechanically that should net you 2-300 RPM. But, because you gained another 30hp, you pick up 600 Rpm. It's a fine line, but you have to remember......NOTHING touches the water to transfer energy but the prop. I see people have props as an afterthought. They will spend $5000 to get 3 mph, when a couple hours at a prop shop with a cupping hammer would have the same result. We used to cup our racing props on the trailer ball!!!! Lab that Mercury! LOL!

So spend some time with them and get them where you want them. Makes a world of difference.

TruxtonFox

Getting the props I have reworked is on the To-Do list, I will get some pics posted up here in just a few, they are pretty bad as far as edge contour goes. I have called a couple of the local boat places but none of them seem to want to touch props.

Padraig

Call BBlades.

CDShack

Are you Stephenville Texas? If yes, call B&B Propeller Service in Ft.Worth.

TruxtonFox

Ok, I'll give them a call in the morning , thanks CD

Rookie

iTrader: (4)

You are never going to be able to spin those 25's. A stock big block 330HP scarab with bravo drives came with 23's and ran around 63mph. I have run the 25's to 80mph but I have 550HP/side big blocks. I suggest you fix your 21's and tachs and then baseline from there. You want to spin you engines to peak HP. Lugging the engine in lower RPM's near peak torque is torque loading it. And I personally would not do that. I believe you need to be around 4800 RPM.