Prop pitch range on Force 125

[capri1600]

I have a white Force 85 and a white Force 125 outboard. What is the typical range of propeller pitch for the Force 125? I know the 85 isn't supposed to get more than 19". How about the 125?

Marty
http://www.martyhammersmith.com

 

[BobList]

Re: Prop pitch range on Force 125

I have an '88 125, on a 16'7" fish and ski Cajun. My prop is a stainless 13 / 17, whatever that means. Someone add to that, please!

Bob

 

[pnwboat]

Re: Prop pitch range on Force 125

I have a 1988 18 FT Bayliner Cobra w/original 1988 125 HP motor (dark blue). Lower leg gear ratio is 1.73:1. Pretty sure this is what yours is too. Most pitch I could run with this set up was stainless 17 with slight cup, top speed 41 MPH on my GPS at around 5100 - 5200 RPM.

Switched out the lower end from a 1988 85 HP (2:1 gear ratio) and am able to run a stainless 19 pitch w/no cup, 44 MPH at 5600 RPM. Dramatic improvement in the hole shot. The engine behaved like a different motor. Later model 90 - 120 HP were anywhere from 1.93:1 to 2.3:1 depending on what year/model. The four cylinder motors really like the gear ratio around 2:1.

I haven't heard of anyone running more than a 21 pitch on a 125HP. It all depends on the weight and hull design.

 

[capri1600]

Re: Prop pitch range on Force 125

Yeah, I hadn't really considered the lower unit gear ratio. I'll have to look into that. I was just assuming since the 85 was handling 19 pitch that the 125 would take 21 pitch.


Marty
http://www.martyhammersmith.com

 

[Frank Acampora]

Re: Prop pitch range on Force 125

I regularly swap all my lower units to the 2 to 1 ratio. By using a higher pitch prop I can gain about 5 MPH this way. Seems that it takes less horsepower to turn a higher pitch prop at a lower rpm through the water, leaving more horsepower to drive the hull.

Example:1.76 X 17 pitch almost exactly equals 2.0 X 19 pitch in inches traveled forward per revolution. Yet, with the 2.0 X 19 pitch the boat is about 5 MPH faster.

That 14 footer I showed you in your Force post has had the lower replaced with a 2 to 1. The 125 now turns 5900 RPM with a 21 pitch cleaver and goes 60 MPH.

 

[capri1600]

Re: Prop pitch range on Force 125

Yeah, it's this sort of optimization I need to look into. When I drop my lower this winter I'll check the ratio. I imagine it's easier to swap the lower unit for a 2:1 unit than to make gear changes to the existing lower unit?

 

[pnwboat]

Re: Prop pitch range on Force 125

I would imagine that it's much easier to swap lower units than to modify existing one. Need special pullers, alignment gauges shims etc., etc. to modify existing one. Also difficult to find the gears. It can be done without those special tools, but probably difficult (and more expensive) to do. You can swap the lower unit in 30 - 45 minutes easy. Who knows how long it would take to swap the gears (if you could find them). Only way you'll probably find the gears is in a 85 HP lower which you already have.

 

[Frank Acampora]

Re: Prop pitch range on Force 125

Doesn't really matter. In the early one piece lowers the gear paks are interchangeable. However, when changing gear paks, you need to shim the lower so yes, it is a little faster to swap lower units.

AND, you can check the ratio by turning the flywheel two times in forward gear with the prop hard against the dogs. If the prop turns once it is 2 to 1. If it turns 1 and 1/4 or so, it is 1.76 to 1. Early units did not use any other ratios.

BTW: If you have a good running 125 DEFINITELY put it on the GT 150 with a 2 to 1 lower and a 21 pitch stainless prop. You are gaining about 45 HP and only about 30 pounds. You would expect up around 60 MPH.

 

[capri1600]

Re: Prop pitch range on Force 125

I actually have a GREAT running 125 with even 148-150psi all cylinders. I'm looking for something to put it on. The GT-150 was never rated for that much power but that would be cool!

 

[stevetheplumb]

Re: Prop pitch range on Force 125

i have a 21ft bayliner with a 120 l drive i can achieve approx 35mph at 5200 on a 13 1/2 x 17 aluminum prop. my question is would a normal outboard gearbox fit the l drive and do the 90 and 85 both have the different ratio? what would you guys recomend to getting more speed ? im hoping that the 90 will have the 2-1 ration and that i could go to say a 13 x 21 stainless prop and get something like 45 mph does this sound right or is it not worth the bother ?

 

[Frank Acampora]

Re: Prop pitch range on Force 125

Marty: The GT is rated for 90 but you really won't be overpowering it. For example a Merc 90 will make your 125 look sick. AND in the movie, it was equipped with an OMC 135 for the jump. You have a hot little go-fast boat and she will look and perform better with the 125.

The photo is kind of junky but here is my V153 also rated for 90 with a 105 on the back. That's the engine in the avatar. I am using a 21 pitch uncupped stainless prop on it. However, on this boat I only get 45 MPH.

 

[kfouryou]

Re: Prop pitch range on Force 125

I'm wandering is changing the lower end of a 125 hp for a 85 hp good for yrs 88 and lower.Also do you have to match up the year or are all interchangable.I have an 87 125 hp, Very sorry if i hyjacked

 

[capri1600]

Re: Prop pitch range on Force 125

The lower units are widely interchangable. Please start your own thread with this topic and the years you are trying to combine and I'm sure someone will know if they'll mate properly.

 

[stevetheplumb]

Re: Prop pitch range on Force 125

sorry i didnt realise that i had to start another thread seeing as its the same subject