Alpha Gear Ratio

[21eagle]

I have a 1989 alpha 1 drive what gear ratio is it????? Can I put 1.32 upper gear in this drive with a 350mag for a few mor mph???? Thanx Chris on prop calculator the 1.32 would net me about 7mph

 

[John_S]

Re: Alpha Gear Ratio

If only it was that easy. If your 350 mag is within its wot rpm range now, you will not gain anything going to a different ratio. You would end up spending money on the gear change and a new prop with less pitch, to get the same, and maybe less performance.

 

[Bondo]

Re: Alpha Gear Ratio

Ayuh,.........

If ya ain't got the Horsepower,....... Taller gears will Slow you down........

What are you running for a Prop now,..??....

 

[180shabah]

Re: Alpha Gear Ratio

That 7mph gain is based on the false assumption that your engine will still be able to turn the same RPM's.

IT WON'T.

 

[21eagle]

Re: Alpha Gear Ratio

the prop i am spining is a 21 pitch stainless. In theory the engine should turm the same rpm tho right???

 

[21eagle]

Re: Alpha Gear Ratio

if i do a 454 swap in boat do i have to change to a 1.32 gear?? Is it better if i do??? I have a 400hp 454 i was just afraid to put it behind the alpha thanx a lot for all your replies Chris

 

[imported_TheMan]

Re: Alpha Gear Ratio

Alphas aren't meant for that much HP.. You'd likely burn it up pretty quick.

 

[John_S]

Re: Alpha Gear Ratio

I think Merc has already proved that lessor 454's (320HP) and alpha 1.32 ratio drives, are not a good match. Too much torque for an alpha. I think they sold them for 1 or 2 years, but had allot drives fail. If you babied it, they might hold up. But, whats the point of having the power if you can't apply it?

Not a Bravo expert, but believe 400HP is getting near the limit on them, as well.

 

[mkast]

Re: Alpha Gear Ratio

It's been an excepted fact that Alpha's behind a big block don't last.
In the real world, Mercruiser did use a big block Alpha combination for two years. The bulk of these installations were in 5,000+ pound, 24+ foot hulls, I know a guy with one. Original owner, older guy, takes great care of the boat. This was before drive showers and synthetic gear oil.
Owner/operators, being true boaters, throttled up, "Goin' across Lake Michigan in one hour!". Drive came out of the water when the hull reached plane, gear lube broke down, drives burned up.
The whole problem was the hulls were too heavy for this power package. Take a 3,000 pound hull, including power package, 23+ foot boat, gear ratio of 1.32 to 1, and you'll have a boat that will last forever if you don't get drunk, and on a dare, try to tow start the truck using the boat.
Mercruiser used the 1.32 to 1 gear ratio in high torque applications in the Alpha drives, like the four barrel MCM 255 hp 351 Ford. Apparently, Mercruiser thought the 351 put out more torque than the four barrel Chevy 350.
(I just may have signed my own death warrant, duck, it's going to hit the fan)

 

[180shabah]

Re: Alpha Gear Ratio

the prop i am spining is a 21 pitch stainless. In theory the engine should turm the same rpm tho right???

Nope.

If you change props or gear ratio, WOT RPM will change also. When changing from 1.5 to 1.32 that change will be negative, and your engine will no longer be making full power.

I also see that you have a 454 ready to go, do yourself a favor and scrounge up a bravo to put behind it.