1988 V20 steplift/305 chevy, mercruiser drive.

[THEFERMANATOR]

Originally Posted by brisboats

Mercruiser put the alpha one behind the 454 for a time and it was a disaster. The torque of the big block would wipe the upper gearset in hard use. The alpha is good for about 300hp and you cannot run it like an offshore powerboat when you have a hot smallblock even with a drive shower and extra reservoir for the fluid. Car hot rod modifications do not really work all the time for boats, your rpm range is to high.

Brian

And that 454 ALPHA had a custom set of 1.36:1 geras in it built just for the extra torque and it BOMBED!

[spareparts]

The 1.5 HD gears were actually stronger, the 1.32 had too small of a driven gear. I had a customer that ran a 720hp Troy Dennis blower motor in front of an Alpha SS. he changed the lube every time out, never drag started it, rana duel shower and usally only ran other boats from 65 on. We had the 1.5 HD but ran out of prop options, ended up with 1.32 and a 27 Mirage(double cupped and labbed), biggest prop we could find with a rubber hub(pre plastic hub days), boat radared out at 101. I still put a fresh set of upper gears in every spring

[UBHSTRY]

Ok, could you help me with the location of what would identify exactly which outdrive unit I am working with?

[spareparts]

88 should be an Alpha 1 generation one. The top cap on the upper unit should have a flat top. Gear ratio should be stamped on the side on one of the decals. You're gear ratio snould be 1.65. IF you happen to pull the upper unit apart, drain the lube and look for small marks on the teeth, they should be timing marks(only on the 1.65), the gears will have the same number of teeth on each gear. Lower unit should have plastic insert type water pick ups vs molded in water holes. The only way to be sure you're lower is an Alpha is when you drop the lower to do a water pump, it shouldn't have a small spring loaded pin on the vertical drive shaft. If you decide to build a 5.7, you can switch to the HD 1.5 gear ratio upper gears, just know it takes specific tools to set up the gears

[brisboats]

Spare is right the 1:5:1 HD are the gears to have AND you still have to be very very careful. Running the sticks like you are Reggie Fountain will only put lots of money in your mechanic's pocket. Personally I think the 5.0 warmed over would be plenty of motor for a V-20. Making a 300hp 5.7 is easy but with this hull I think you would be reaching very diminishing returns.

Brian

[brisboats]

Forgot to add 1988 puts you square in alpha one generation one category but you never know what someone may have bolted on over the years. External clues are the flat top on the upper gearcase, and a squared off cavitation plate on the lower versus a rounded one. Funky drives are the lowers from 83-somewhere in 85 they will have the newer case with a square cav plate but the earlier internals, smaller shaft and a preload pin. Like Spare said you really won't know what you have until you open it up. Count your teeth in the upper gearset I have seen some 5.0 come with 1:5:1 ratios too.

Brian

[UBHSTRY]

Ok thanks guys. I am going to take a real close look when I pull the boat back in to drop this engine in.

[UBHSTRY]

Ok, fired the engine up this evening....well, sounds healthy. Going to spark limit it to 4800rpm to possibly 5200rpm, untill I can figure out the drive situation. My biggest fear is the thing pulling up from the hull. I have it strapped down, just in case something goes horribly wrong. Man alive, this thing should be in a car (The gentleman has a really nice 88 7 series BMW I did for him, and keep telling him he should let me put it in that.....lol) Possibly a different drive unit altogether? What does it take to be able to reliably spin an out drive to 6500rpm? What fails? Bearings, or gears? Jet drive possibly? Or am I just off my rocker, and keep it dialed way down? (hm...way, way down)

[macojoe]

that 5200 is about right!! 6500 you will blow the motor i would bet!!