Alpha One Upper Gears - Are there HD versions?

[76SeaRay]

So, I am getting ready to reassemble the upper unit and was wondering if they make Heavy Duty versions of the gear set. The boat is 22ft hardtop so must be about 3650lbs dry weight, the 5.7L new build should come out right about 300hp, and my current upper gear teeth counts at 1.50 to 1... This is a cruising boat, not interested in slamming hole shots... Since I am on the high end of the Alpha One for horsepower am wondering if I can get a little more margin with 1.50 to 1 "HD" gears if they make them...

Thanks....

 

[Scott06]

the heavy duty alpha parts is called a bravo drive.... seriously don’t think so as anyone who is making a lot of power will run something heavier than a alpha. You see a fair number of folks running 383 s with alphas , based on your use you don’t anything upgraded if the alpha is in good condition.

 

[JASinIL2006]

You will be fine, especially if you go light on the throttle. There are lots of 5.7s in front of Alpha Ones.

 

[76SeaRay]

Ok, thanks... Just thought I would check before assembling.. All of my gears are in good shape and I am putting in a new lower housing, bearing carrier, all new bearings, seals and waterpump..

 

[achris]

Yes, they make a heavy duty gear set. No, it's not called Bravo!

Standard 1.5:1 gear set is part number 43-18411A2, Heavy duty 1.5:1 gear set is 43-118410A4..

 

[Scott06]

Yes, they make a heavy duty gear set. No, it's not called Bravo!

what did you guys loose your sense of humor down there?
i guess the question is should the OP replace what he has or is it not needed for his application

 

[76SeaRay]

Thanks, I will look further into the HD gear set... Yup Scott, I caught the humor....

 

[76SeaRay]

Well, after looking, the only place I could find gears using the Mercruiser part number is Sterndrive Engineering. They don't say Heavy Duty but use the HD Mercruiser part number. The ratio says 1.47 to 1 so just guessing here that they are 1.47 to 1 because they are Heavy Duty?? Mercruiser does say their part number for the Heavy Duty is 1.50 to 1 though...

 

[Rick Stephens]

What SEI offers is china made copies... may not be anything wrong with that.

Knowing the Alpha drive is fairly well balanced on component strengths, seems like if the gear set is actually stronger for the HD version gears, the failure would just move to another part of the gear train. Also possible that the gears could be made with a harder and deeper surface hardening, or with a hypoid design that spreads the load across greater tooth surface. All moot if the most common failures come into play - low oil levels and broaching under high power.

 

[76SeaRay]

Well, the HD gears are pretty expensive and I don't pan on running the boat hard (cruising mostly) so thinking I will just stay with the gear set I have.. Thanks all..

 

[achris]

.... The ratio says 1.47 to 1 so just guessing here that they are 1.47 to 1 because they are Heavy Duty?? ...

A few years ago Merc changed the tooth count in the lower housing, from 17/28 to 13/21. Apparently it was done due to 'gear noise' on the 17/28 set. Anyway, those gears have a slightly different reduction ratio (from 1.65 to 1.62). Add that to the various tooth counts for the upper and you get 1.5 going to 1.47, 1.65 going to 1.62, 1.84 to 1.81 and 1.98 to 1.94. Thta's why you see drives listed with either ratio. Top box is the same, lower has the difference.

Chris.....

 

[achris]

what did you guys loose your sense of humor down there?

Oh, that was funny? Didn't see it as anything but misleading...

3 blonds walk into a bar. You'd have thought the 3rd one would have noticed... THAT is funny.

 

[Scott06]

Oh, that was funny? Didn't see it as anything but misleading...

3 blonds walk into a bar. You'd have thought the 3rd one would have noticed... THAT is funny.

Fair enough, I guess neither of us should quit our day jobs...

 

[76SeaRay]

Hey thanks for the info... Brings to mind that I should count the teeth on my lower gears to see if it is 1.50 or 1.47 but unless somebody changed them (or the whole lower unit) they should be for 1.50 since my serial number is for a 1985 model year...

 

[Howard Sterndrive]

a lot of times people will think their "built" 350 makes 300HP because the engine builder dyno's it at 5800 rpm and gets that number. Then you put it in your boat and it spins a maximum of 4600 rpm and it makes 260HP just like Merc rated it for the alpha application.

 

[76SeaRay]

Well, mine isn't dyno'd. I had the builder do the GM Vortec block and heads and I did the rest. My comment to the builder in giving me the block work up was that 300hp was my top end limit so he provided pistons etc. that weren't over the top in performance. I went with the Xtreme Marine roller CAM to get about .495 lift, roller lifters, roller tip rockers, and a double roller cam chain.. Pistons are hypereutectic at 0.020 over bore. I am going to run a Rochester 4 Barrel.... I didn't worry about quench and squish but maybe the builder did. I would say it is just a mild build... So, all said and done it should come out about 300hp but if it is less, that's fine. My only concern was that if it does come out about 300hp that the gears have a bit of head room over that.