What gears to use

[john200]

I have a 1990 Glasstron 185 originally It had a 4.3L the prop that was on the boat was a 13 1/4 x 23p boat is about 2000lbs the gears that are in the outdrive are unknown Now the boat has a 350 with 350hp so I was told that I need to change the gears can I just change the prop I have a 14 1/4x26p will that work If not I don't know what gears are in the out drive now but I have seen 350s run 1.65-1 ,1.50-1 and 1.47-1 but what ones should I run I have a few different props that I can try starting with a 19p a 23p and the 26p I have a few others but can't recall what they are right now.

 

[achris]

Re: What gears to use

4.3 from the factory could be either 1.84/1.81 or 1.65/1.62, depending on the era. 350s need 1.50/1.47 (depends on the tooth count in the lower gear housing).

If the original is 1.84/1.81 then you will probably not be able to get a prop big enough....

The ratio is stamped on the leg, or if you post the leg serial number we can tell you what is was when is came out of the factory...

Chris........

 

[john200]

Re: What gears to use

Ok well let me ask this then knowing the boat and motor combo I have so what gears and prop should I start with?

 

[wca_tim]

Re: What gears to use

I've run 1.32, 1.5, 1.65, and 1.84 gears in my current 18 foot boat... behind a 383. you can get decent props for any of those gear rations in pitches appropriate for the speed ranges you will most likely be in. I would bet that with the same gear you had (presumably 1.81 / 1.84 based on running a 23" prop behind a 4.3 in that boat, assuming speeds were somewhere in the 50-55 range maybe?), you will be able to turn that 26 inch you mention in your post fine as a starting point and go from there.

When I upgraded the 4.3 in my boat to the current small block, the builder told me with a wink to give it a run with the current gear... I was going to swap to a 1.5... he told me to drop by if I didn't have a prop that would work, etc...

the boat will be faster running props in the 26 - 29" pitch range so you will probably be best served by a 1.8 gear ratio. I know this will probably draw some fire on here, but let's be real, gear ratios were spec'd with engines to give the best performance and durability in the average situation...

just my experience...

 

[achris]

Re: What gears to use

Ok well let me ask this then knowing the boat and motor combo I have so what gears and prop should I start with?

For a 350 V8 you should be using the heavy duty 1.50:1 gearset (depends on the tooth count in the lower box. Merc changed it about 1995 to quieten down the lower box noise, so the 1.50 became 1.47).

Once they are in, then you'll need to experiment with the prop to find the right one. I would start with the 23" and go from there.

To work it out properly you would have to supply us with the boat weight, the drive ratio, the engine power and max revs, and the prop you intend to use... Then use them and give us the results.

That's just what I would do... Other people might do something different....

Chris..........

P.S..... 350hp through an Alpha??? Waiting for the BANG....

 

[wca_tim]

Re: What gears to use

it's a fairly light boat and it'll be fine - that 350 you're estimating for hp is at the crankshaft, no? and the 300 max that so many cite for an alpha is at the prop shaft?

try running what you have, get it propped right, keep good lube in it, maintain it well and run it like you stole it. You'll be pleased with the result.

the vast majority of drives that fail do so because the owners don't maintain them.