Re: Will it hold up?
idk about the story regarding Fountain and alpha drives, but I can ask the guy that used to build a lot of their performance drives (need to call him next week to have the gear ratio changed in my alpha ss drive) and the guy that built a lot of the upgraded engines. (built the longblock that's in my boat now - best machinist / builder I've ever dealt with bar none)...
I've run 1.84, 1.65, 1.47, and 1.32 gears in my current boat.
Generally speaking, IF you're choosing gear ratio based on performance alone, you want to choose the gear ratio that will get you in a prop pitch to diameter ratio of something like 1.8 - 2.0 to one. My current boat started life as a v6, I bought it with a trashed motor in it for a learning project. I was all set to get a different drive with a 1.5 ratio, but the the guy building the engine told me to try it with the 1.84 first. I'm sure he knew it would be faster... he was right, it's a good bit faster with the higher gear ratio - because I can turn props that are more efficient.
For the 13 1/2" - 15" inch diameter props that will be right for your boat, that magic range is in the 27-29" pitch range. If starting from scratch, choose a gear ratio that puts wide open throttle rpms right where your peak horsepower is. For a light shallow hulled i/o assume that's 5000 - 5500 rpms and a speed of something like high 60's to mid 70's. works out perfectly for 1.8 gear ratio... for more power, 1.65...
Note that this has nothing to do with the strength of the gear set and the 1.5 and 1.32 gears can be had in heavier gears, AND because the lower pitched props don't couple as hard with the water, it actualy puts a little more strain on the drive to run the higher gear ratios. I understand that you can offset it some by having the diffuser ring cut off the prop (helps it cavitate a bit out of the hole and slip, or running a vented prop if yuou're running some or all the exhaust through the drive.
The anlogy to think aobut is on a car with a lot of horsepower. street radials will spin out of the hole and make the holeshot a little slower, but they are easier on the drivetrain. Put decent slicks on a car that does fine on radials, now it hooks up much faster and all of a sudden things start to break.
anyhow, the difference in top speed was something like 2-4 mph per step in gear ratios, with the caveat that the 1.32 ratio is an alpha ss drive - shorter and with a different shape. It runs about the same speed as the 1.84 gear ratio did - upper 70's. I've never had any issues with hole shot. for all of the set-ups, when propped to put wot at peak horsepower rpms, it has always had plenty of power out of the hole to stand it up on end, pull skiiers out, etc... without ever putting the throttle down hard.
btw, torque is a measure of how much acceleration / seat of the pants power you have in a boat, horsepower - if your propped right - sets max speed.
I went through the exercise of playing with props and set-up for each drive / gear ratio. and the numbers I'm talking about are with the best prop for that gear. I spent the most time optimizing with the 1.84 and am going to have the alpha ss switched to 1.65 because I think I'll be adding enouhg horsewpoer and speed that my best props from earier with 1.84 wil be spot on. although if I'm told that the heavy duty 1.5 gear set is that much stronger, I'll go with 1.5 after the upgrade...
the best (from memory) were...
1.32 19" predator mid to upper 70's
1.5 23 or 21" laser 2 mid 70s
1.65 26" turbo 3 blade, 25" mirage (I think a 25 or 27" laser 2 would have been perfect, but didn't get one to try..)
1.84 labbed cut down 28" mach 4 sterndriver, 27" mirage plus, cut 29" Hydromotive quad iv intimidator upper 70's
Sorry for the book - I was sitting here watching kiddo do her homework and got carried away. Note that I'm more of a backyard hack - not an expert or authority, but I try to do my homework and think through things... Hope this is helpful...
ps. note that once you start getting into the 70s, you have to worry more about chine walking, gear case blowout, and your boat getting squirelly... the ss drive on mine makes a huge difference in handing at speed. the point is you need to wear the lanyard and kill switch, and make sure your steering, etc.. is in great shape. Much more and think hard about hydraulic steering, etc...
we had a guy die a few months ago here - no alcohol involved, speeds not overly excessive... one lost control of the boat, perhaps from an equipment failure and it turned sharply in front of the other. the driver caught the prow of the slightly slower boat in the head and died on the spot. Both were experienced drivers in their 40's who grew up on the water and racing boats. safety equipment, etc... may have made the difference. THy weren't close friends or anything, but we stopped and shot the breeze for a few most sat / sun afternoons when everyone was out playing... Just food for thought.
