gear ratio question
 

i have a 88 four winns liberator has a 454 merc. found out the bearing on the driven gear went out and while im in it was wondering if i should stay with the 1.32 to 1 gear ratio or if theres another route i could go that wont take any top end out but give me a little more torque? this is all kind of new to me so any advice will help .. motor mainly stock and will be getting a m1 within the next year so if that changes anything?

its the lowest gear u can get, well they make a 1:25 but its not that much of a differents.

Comparing in terms of numbers that is a low number but in all actuallity the lower the number the higher the gear ratio. That seems to be geared actually high for a stock 454. It should be a 1.5 to 1 or more. A little more info is really needed. Is this a single engine? How big is the boat. What drive is it? Most important what is the maxium RPM the boat will turn now at WOT? What is the Horsepower? Also what pitch prop are you running? I my opinion I believe you most likely need a lower geared drive like a 1.5:1.

Just guessing I would think your boat is hard to get on plane and hard to idle around the docks.

ya your right its stupid hard to get on plain..its not bad to dock or anything at all tho but its a 24ft four winns liberator has a single 330 hp 454 merc in it... cant remember what pitch on the prop i think 23 or 24 maybe but dont know..

runs right at 4k rpm i believe.. its been about a year since ive had it on the water..and its just a alpha one gen 1

U def. need a 1:50 for that boat your rpm should be 4600-5000 !

I'm surprised that drive lasted this long with that high gear in it. They only put the alpha behind the big block for a very short period. Your prop is probably more like a 19 or 21 pitch. You may want to go to an even lower gear than a 1.5:1 to help preserve the drive. I believe you can also get 1.62:1 and 1.81:1 gears. This will give you more low end power and the motor will be able to turn more RPM's to keep your top end speed.
I don't know the story behind this boat but it never should of had a 1.32:1 gear drive on it. May want to double check on that gear ratio, I'm not so sure they even made a alpha with that high of a gear in it.

good to hear because i can find a 1.50 to 1 ratio upper everywhere i have had the hardest time getting 1.32 to 1 parts or anything.. its the factory outdrive and gears my dad bought the boat new in 88 and i just bought it off them about a year ago.. big mistake.. we boat on the lake of the ozarks mainly and ill never own anything under 35 foot again..

once propped right, the boat will be faster with a lower gear ratio on it (higher nyumerically). for the range you're running you might pick up as much as 3-4 mph for each step from 1.32, 1.47/1.5, 1.62/1.65, 1.81/1.84, and you won't be able to find good props in the range required for 1.98/2.00.

why? because more gear reduction (higher numerical gear ratio) means more torque at the propshaft and the ability to turn a higher pitch prop.

You ideallly want to prop to put you in the 27-29" pitch range I would imagine. BUT in terms of holding up, the 1.32 and 1.5 gear sets can be had in a heavy duty version (maybe all of the 1.32 gearsets - I should know, that's what i've got on my boat right now, but I don't...).

the 1.32 was an attempt to make the alpha drives live by lowering the torque on the lower gear set - the more mechanical reduction you have the more torque you have.... also the more prop you have, the more resistance it will have to being turned at low rpms and so the mroe strain it will put on the whole drive. It was a decent idea in theory, but the problem is that the entire drive is just not designed heavily enough to hold up to typical use under typical maintenence conditions in many boats with bigblock torque...

that's my understanding at present anyhow...

bottom line - go for a 1.5 ratio drive with the HD gear set in it...

oops...

You really should switch to a Bravo 1 especially if you plan on puttin an M1 on the motor. No way the Alpha will last with that.

Actually the ideal pitch range for that boat would be 19-23 with a 1.5:1 gear ratio in your drive. If you are able to spin a 27-29 pitch prop than it would be time to consider a higher gear ratio in your drive. Not all but most of the props Mercury makes are between 15 and 25 inchs of pitch.

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

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:drink::drink:

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.

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

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

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

upper drive shaft
 

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

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

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

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