scarab 22 switch alpha to bravo any tips or thoughts
 

I have a 94 scarab 22 trying to swap outdrives from alpha to bravo. What would be the best way to go about it?

Find a good Bravo Transom and Outdrive - drill two more holes - bolt it up .... if your using the same engine you'll need to add an engine driven sea water pump as the Alpha is in the drive - Bravo is engine mounted...

This might be a silly question, but why swap? The Bravo will take more HP than an Alpha, but you're going to loose speed due to greater drag.

I'm trying to go from alpha to bravo. Does any body know what gear ratio i need? Also are the deminsion's the same beetween the alpha and bravo as far as the distrance between the prop and the boat and does that affect anything if it is different?

Before you continue with the question below, I suggest, you adress this question. Are you looking for advice, or just someone to confirm your own ideas?

Second. Yes. The X-dim on the Alpha and the Bravo are the same, more or less. I think there is 3/13" diff. You are asking about gear ratio??!! We don't even know what engine you are running, and what your current drive ratio with the Alpha is??? Current GPS speed @ ??? rpm and prop model/pitch. Are you looking to upgrade your power? If not, LEAVE WELL ENOUGH ALONE! If your are not running big power, the Alpha is a much faster drvie.

I am currently running the 5.7l with 260hp would eventually upgrade with a new small block producing around 400hp. RPM's are about 5200 @ 55mph with a 21p prop.

The alpha will hold up fine.Just don't air it out and return to water without letting out of it.JOHN SR

So you think the alpha will hold 400hp?

If it blows , just put on one of those life time replaceemnet ones for 700.00

lifetime replacement?

look on the web there is company that makes replacement drives for alphias and they give the no questions asked life time replacement really they are import ones

Those drives are great,you break it or whatever they will replace. Yes that alpha will hold 400 hp.We were running a good 330 hp thru one in out little 202 stinger with no problems running hard to 80 mph.I would think a 1.65.1 ratio,let you spin a little more prop,what you loose in reduction you make up in pitch. We are getting ready to run 550,600 hp thru one now on the stinger. JOHN SR

The alpha will be fine . Your boat probably only weighs like 3 k

I run 450+ horsepower through an alpha drive in my river boat (383 forged crank, pistons, etc, comp ported afr195 heads, imco powerflow exhaust, airgap rom intake, comp cam, etc...) - because it is a little faster than a bravo would be and for the cost of converting to a bravo, I can afford to lunch a few drives. The aftermarket drives have a 3 year warranty and are more like 1300 for the entire new drive. If I were looking to add a lot of power, I'd look for a bigger boat that as built for it. In your light boat, I'd set the money aside and buy a new drive if you lunch it. Just maintain it carefully - most people that blame the drive for failing, caused the problem by not keeping up with the maintenence.


the 1,6 gear ratio in an alpha drive might not be such a great idea for pushing the power limits. I believe that of the merc alpha gear sets, the 1.61 / 1.65 is the weakest upper gear set and teh one that is most sensitive to being set up correctly. I've run 1.81 / 1.84 and 1.47 / 1.5 gear sets behind 400+ hp without issue. Note also that as you go to more mechanical advantage (ie 1.81 vs 1.5), you'll be able to go a bit faster with the same amount of power once your propped correctly. If you get crazy with poser, coling may become an issue though - remember that the impeller is driven after the uypper gear set and so slows doan as the gear ratio goes up. That being said, I've not had a problem with that yet...

Hope this is helpful

So i should replace my upper gearset with a 1.81/1.84 and which prop should i run looking for 70mph.

you're probably going to need more than 400horsepower to get that boat to an honest 70 gps...

then again, most 70 mph boats are really 60 mph boats when the radar gun or gps comes out. ;-)

it's cheaper to buy another upper than to swap the gears out unless you have the tools and do it yourself.

the reason you get more speed out of a higher gear ratio is because you can run props that are more efficient at making speed - typically modern props with ratio of pitch to diameter 1.8-2.

remember that when you run a higher gear ratio you multiply torque on the prop shaft - now we're talking about 700 ft bls of torque...

I would stick with the 1.5 ratio for now, maximize other things, add some power and see what you get.

Just my two cents - not an expert, just a backyard hack...

I agree.....I'm running a ~400hp bbc through my alpha and havent had any problems. plus my bbc probably has close to twice the tq your sbc has and my boat is prob 1.5x the weight. just be careful airing it out, and don't whack it out of the hole. the drive will last as long as the nut behind the throttles will allow.

Look at it this way...The good news about alpha drives is that if you DO do hole shots and DO air the boat out and damage the drive, you're only out about 1,200 bucks for an SEI drive. You can find used alphas for 5-700 bucks. Compare that to 2k or so for a used bravo and and anywhere from 3k to 7k for a rebuilt or new unit, and the drive issue becomes moot.

It would probably be a good idea to invest in a good drive shower to keep the uppers cool. Also, frequent lube changes will extend the life of a drive under heavy load and give you more warning of impending failure.

Try to keep your idle down, and be reasonably forceful when putting it in gear. Those folks who try to ease an Alpha into gear and get the grinding sound will seriously shorten the life of the dog clutches that engage the gears.

i also agree budman...i can't tell you how many people i've had the "snap it into gear" conversation. if it grinds, you didn't do it fast enough. it should be a solid...clunk!

drive showers are worth their weight in gold!! it seems just recently they have become more popular for the alpha guys (seen them forever on bravos), but i've always been a believer. i always get a jolt out of the people with chalky white uppers....its a ticking time bomb. a few days later and you see the very same boat being drug in by seatow

another note... drive shower or not, running through hull exhaust is smart - the water running through the drive to the engine helps cool the drive and exhaust you run out helps to heat it - this is much more of an effect when you're running fast - you're generating more hot exhaust, more friction from the heavy load and your drive is up further out of the water. it makes a huge difference... I've never had the white chalky stuff on an alpha drive (and I run the snot out of it on a regular basis) but have never run much power and also run exhaust through the drive... A local offshore guru explained that to me, told me they usually take drive showers off alphas, to run good synthetic lube and not a problem. That has been my experience.

the advice about being firm when shifting into gear is goood advice. also, some folks around here with longer duration cams requiring higher than advised idle in front of an alpha drive mount a push button bypass to the neutral safety switch under the dash and start the engine in gear the majority of the time... My understanding is that shifting into gear is a major event in catastrophic gear failure. putting it in gear puts a small chip in a tooth which becomes a sight for larger fracture and breechs the hardened gear surface. broken metal ensues.

My experience / understanding is that the majority of alpha drives that fail because of too much power, would not have failed if someone had done a better job with maintenence. I have to admit that the upper drive I burnt up recently was my fault - I boogered up the seal between the drive and gimbal housing and got some watter in the bellows, it leaked into the upper and the result was a burnt up bearing set and some really nasty broken teeth in the 1.32 gearset.... that and a bunch of gear lube that looked like metal flake paint or pudding.

As mentioned above, If you're going to push anything near or beyond it's design limit, use high quality synthetic lube, make sure the level is right and change it often.

1.5 ratio

I am interested in this "lifetime replacement" Alpha drive. I have a similar setup!

Alpha One tip
 

Biggest thing you can do to make your drive survive is to use a GOOD Synthetic gear lube. This goes for all stern drives. Dino lube can not outlast or protect as well under high shock loads.