Alpha One Gear Ratios

[Tubingluvr]

The 4.3 4 barrell and the 5.0 2 barrell require different gear ratios....can anyone tell me why ?.....there is only a 15 hp difference and the same WOT....I don't understand ?

 

[Bondo]

Re: Alpha One Gear Ratios

The 4.3 4 barrell and the 5.0 2 barrell require different gear ratios....can anyone tell me why ?.....there is only a 15 hp difference and the same WOT....I don't understand ?

Ayuh,.... Yer question is to general, as both those motors can use 1 of 2 different ratios, dependin' on the application...

 

[Howard Sterndrive]

Re: Alpha One Gear Ratios

because manufacturers tend to gear a drive so it can use a 19P prop. 19 is the most efficient pitch (generally).

 

[Tubingluvr]

Re: Alpha One Gear Ratios

My boat originally came with a 4.3 vortec 4 barrel.....there is currently no engine and I would like to put a 5.0 in it but not if I have to change outdrive.

http://www.getboatgear.com/selecting-boat-outdrive-gear-ratios.php

 

[Tubingluvr]

Re: Alpha One Gear Ratios

guess i shoul have said I have a 1.84

 

[Howard Sterndrive]

Re: Alpha One Gear Ratios

unless it's a big heavy boat, I don't think the 1.84 will be good at low elevations (Michigan). You can always try it with a higher pitch prop... no harm in trying, but you might find you need a 25P or steeper and those tend to blow out on i/o's in turns and are poor for holeshot... but you might find a 23P does the trick.

but I would go 1.5:1 for a V8. In fact, why go 5.0 when you can go 5.7...
An additional bonus to the V8 ratio drive is more impeller flow for cooling the bigger engine.

You can buy a brand new upper gearcase in your favourite ratio for about $650, and probably sell your used V6 one for a couple hundred.

 

[Tubingluvr]

Re: Alpha One Gear Ratios

unless it's a big heavy boat, I don't think the 1.84 will be good at low elevations (Michigan). You can always try it with a higher pitch prop... no harm in trying, but you might find you need a 25P or steeper and those tend to blow out on i/o's in turns and are poor for holeshot... but you might find a 23P does the trick.

but I would go 1.5:1 for a V8. In fact, why go 5.0 when you can go 5.7...
An additional bonus to the V8 ratio drive is more impeller flow for cooling the bigger engine.

You can buy a brand new upper gearcase in your favourite ratio for about $650, and probably sell your used V6 one for a couple hundred.

Will the aftermarket upper that iboat sells work on my mercruiser or are aftermarkets not interchangeable with original mercruiser

 

[Don S]

Re: Alpha One Gear Ratios

The aftermarket uppers from iboats are SEI, and they will work interchange with OEM.