wtfo

for performance in boats that will run 50+, well designed props with a pitch about 2 times diameter are the sweet spot (for an alpha drive, that's 13 1/2 - 15 inches diameter, ca 27-30" pitch). there are lots of props around in that pitch range. note that's from a performance standpoint, not necessarily a convenience standpoint. good examples of merc props in that sort of range are mirage, laser 2, and others... once you start looking outside merc props, there are a number of really good options... imho

bajabob

ok i have 540 dart . 1000holley carb dart pro1 heads dart sinlge plane intake msd stainlless headers k/n flame arestor 100 gallons fuel boat ran 76.7mph trim tabs to long to low i cut 6in .took another run 78.8 mph gps . that was at 5400rpm i nam runnig a 136bravo1 drive with a 23mirage prop . you say you are truning 4000 you need to go down3pitch that will give you 4600rpm then the boat will run better!!! each pitch is 200to 300rpm depending on the make of the prop . i find mirage prop is 200rpm. change the prop is cheaper then the drive

picklenjim

Never heard of this formula before but it may be true on a all out high performance twin engine boat, I don't know. However the boat in question here is a 24' single engine with a stock iron 330 Alpha. There's no way that boat would ever turn a 27-30" pitch prop. Not even with a 1.5:1 gear. Look at bajabob's ride. He's probably running 600+ HP in a 24' baja and is using a 23" pitch mirage. My 23' Nordic is probably running 550 HP and I spin a 25" mirage in the mid 5000 range with 1.5:1 gears. Just aint gonna happen. In my opinion it will need a 19-23 at the most with 1.5:1 gears.

bajabob

you are rigth !! i say try a 19 pluswill most likely be the prop to use . you need 600hp to trun a 23!!!!!

wtfo

it would turn a 27"+ prop with a 1.8 gear in it.. and it would be a bit faster that way...

I've accumulated an odd assortment of articles from old boating magazines, engineering journals, merc and other manufacturer tech docs and posts from various message boards. That combined with actually running a series of gear ratios and propping each one bears out very clearly what a locak high performance marine engine builder told me a few years ago... he told me to leave the 1.84 gear ratio in my boat and it "might" be faster... dead on because that hed me turning 27-29 inch props...

that assumes you're strictly interested in performance and not owrried about the fact that especialy since you can get hevier duty 1.5 gear sets, the reliability (whatever you have) is going to be better with the 1.5 or 1.32 gears. My 17 1/2 foot (ski boat" wink, with alpha (SS) / 450+ hp currently has 1.32 gears turning a 23" laser 2 prop to redline as of this am so will go to a 25" for top end days... note that if there's enough blade on a laser 2 to hold behind your boat it'll be faster than a mirage...

My understanding is that it would be REALLY hard to beat a labbed mirage for all around performance in that kind of set up. in whatever pitch needed for the gear, hull and power...

I also agree that an alpha drive is living on borrowed time in there. In a little boat, running redline shoclproof heavy, they'll take quite a bit, but... a bravo with a 1.6 gear ratio and propped accordingly would likely be a much better choice. imho

hoozeyurdaddy

yoiu may want to think twice about a M1 on that set-up, way to much HP for a alpha.

mikeoutlaw24

i have a older bravo one and snaped the upper drive shaft the part #for the drive is 45-812773t i see the bravo x drive has new drive shaft part #45-812779t is this stronger then the one i have and will it work in the older drive thanks mike

jslowss

well the only good part is my dad owns a marina and we have alot of parts laying around.. just came across 2 alpha ones but there the 1.65 to 1 ratios that were with a couple 4.3ltrs out of a sea ray.. i think im just gonna have to try n use one of them for the summer and hold off on the pro charger i guess moneys tight right now and i cant afford to brake anything else this year.. so what pitch prop should i run with that gear ratio? its just a stock 454/330hp motor.. and i do have a mirage prop now im just not sure what pitch but from what i understand i can just have it re worked cant i ? bc it is a fairly new prop

John the Drive Man

Have Alpha I 1.50:1 complete rebuild ready to go. Will let go for a guud price. Call; 954 237 0332 if interested.

mcollinstn

An Alpha behind a bigblock needs as much help as it can get. The numerically lower the ratio is, the less load is on the vertical shaft and bullet gears.

I say you ought to rebuild your unit with 1.5:1 gears and sell it. It will be a popular ratio and should sell well.

Then, buy a Chinese Alpha copy with a warranty and run the dog out of it.

As far as rpm, you need to be around 4400-4500. As long as you prop for that rpm, you won't see a huge difference between the different gear ratios, and your best bet is to run a ratio that gives you a good selection of used props (there are a lot of 21" and 23" Mirages out there..)

MC