Outboard Engine GEAR RATIOS!

**NeedOne** · 11-17-2016, 01:34 PM

Originally Posted by FMP

Hold the flywheel fixed and turn the entire motor, boat and trailer around until the prop/shaft turns one full rotation. Then count the rotations of the engine , boat and trailer .

Thanks. You have to grease the floor so the trailer rotates easier.
And make sure to clean the motor with prop wash after...

**90 5.0** · 11-17-2016, 02:07 PM

Originally Posted by dwilfong

That's my point with the one crank used a gear change will do nothing. The prop is the gear change.

Thats not entirely accurate, weight and motor style have a lot to do with it also.

I know at heavy weights my boat is faster in the 1/8th with a 2.0/22 than it is with a 1.87/20

on a triton we have we had a 225/1.75 and ran a 25p, we swapped motors and went to a 250/1.62. With the same 25p prop we could barely get out of the hole with a full load and livewells full of fish.
We had to go down to a 23 to get holeshot back and it fired out of the hole like a rocket, but then is on the limiter way too quick.
On that boat we cannot prop it to have a good holeshot and good top end with a 1.62 because of weight. But with a 1.75 we can.

Light boats are less effected by gears than heavy boats are because of the torque multiplication factor needed to get moving is less.

Its physics sorry.

**FORBESAUTO** · 11-17-2016, 02:47 PM

I agree, my triton runs better on take off and top end with 2.0 gears and 27 pitch prop than with 1.87 gears and 25 pitch prop.

**WillySteve** · 11-17-2016, 06:30 PM

So....2 wimps with narrow paddles and Tennis Shoes can holeshot 2 big guys with wide paddles and Combat Boots because of the weight diff????
HAHAHA!!!!

**FMP** · 11-17-2016, 07:19 PM

Look at it this way, if you could make up the difference of less gear with slightly more pitch of the exact same prop the top end should be near the same depending on slip but getting there may be different ? As mentioned above in the 1/8 , you are limited by the top end power of your motor but why? Prop drag, did you get the rpm you expected with the taller gear?

**FORBESAUTO** · 11-17-2016, 09:07 PM

Turn both props 7200. Actually ran same speed with same prop just turned it around 400 more rpm. You gain more torque multiplication with gear than you do with prop pitch. Also steeper pitched prop I feel is more efficient resulting in better speeds and acceleration. IMO. My engine also makes more power around 8000 but not practical propping to that for a fishing rig.May not have same results with a stock motor, but it my situation lower gears deffinantly performes better period. Ive tried all types of setups and that's what works best for me.

**FORBESAUTO** · 11-17-2016, 09:32 PM

I guess what I'm saying is the gear change alone did not make boat faster, but with limited low rpm power of modified motor the gear change gave the ability to run a taller more efficient prop that I could not have ran otherwise. I tried about every prop imaginable in the 23-25 pitch range and all ran roughly same speed. But the 27 -29 pitch props run anywhere from 2-7 mph faster. Not trying to stir the pot, just giving real world results that hopefully could help someone else out in a similar setup as myself.

**WillySteve** · 11-18-2016, 07:26 PM

Originally Posted by FORBESAUTO

Turn both props 7200. Actually ran same speed with same prop just turned it around 400 more rpm. You gain more torque multiplication with gear than you do with prop pitch. Also steeper pitched prop I feel is more efficient resulting in better speeds and acceleration. IMO. My engine also makes more power around 8000 but not practical propping to that for a fishing rig.May not have same results with a stock motor, but it my situation lower gears deffinantly performes better period. Ive tried all types of setups and that's what works best for me.

Kinda like Ford and Chevy Drag race cars.....A big block Ford makes more low and mid torque than most Chevy's and loves a lower gear ratio, as in a 4.11-4.57......something to pull against vs. the high revving Chevy likes 5.13-6.20's!!!
My old 521" Ford crossed the traps at 143@6800rpm where most of my competitor's Chevy's were more like 143@7500-7800rpm with similar tire size!!!!
I ran a set of 5.13's once and had so much tire spin that you had to feather the throttle.
Bottom Line....A lot depends on the engine's torque range as far as gearing and prop for best holeshot and top end!!!!

**FORBESAUTO** · 11-18-2016, 10:44 PM

I agree 100%, what I was stating is that prop pitch change does not necessarily yield the same results as a gear ratio change. In my situation I gained more by going to a 2.0-1 gear than by going to smaller pitch prop. That's all.

**Chaz** · 11-19-2016, 05:45 AM

I thought it was this simple. Now my head hurts , I'm going back to bed ....

**Magcat 62** · 11-21-2016, 07:04 PM

I ALSO liked my boat with 2;1 v\s 1.87 problem my 2;1 has no lw p/up but it ran same height and pumped ok on my 150. more all around power.i should put the 2-1 on the v220 2.4?r. DONT know about top end if i switch would hope to gain !

**Magcat 62** · 11-21-2016, 07:15 PM

Originally Posted by FORBESAUTO

Turn both props 7200. Actually ran same speed with same prop just turned it around 400 more rpm. You gain more torque multiplication with gear than you do with prop pitch. Also steeper pitched prop I feel is more efficient resulting in better speeds and acceleration. IMO. My engine also makes more power around 8000 but not practical propping to that for a fishing rig.May not have same results with a stock motor, but it my situation lower gears deffinantly performes better period. Ive tried all types of setups and that's what works best for me.

seems that 400 rpm is wasted by slip if boat ran same speed same prop ? doesnt seem right? ART

**Magcat 62** · 11-21-2016, 07:31 PM

Originally Posted by dwilfong

That's my point with the one crank used a gear change will do nothing. The prop is the gear change.

WRONG! Gear change is adding prop torque pitching up your adding load and rpm should drop unless your way out of power range

**Magcat 62** · 11-21-2016, 07:51 PM

[QUOTE=dwilfong;2900840]The prop is a fluid coupling. As the set up on the boat changes it will grab more or less fluid (water). Like I stated the TIP SPEED has a lot to do with what gears you need to keep the prop shaft speed in line with prop diameter/pitch and the torque curve of the eng. That is what the gears in the lower do.
With a ie i agree i terms of power head part but 2 huge variables pitch and prop rpm can move power curve dramatically due to the fluid prop coupling. a 2.5 2;1 will have more dynamic power than 1.87 in a marine enviroment. it has to!

**Magcat 62** · 11-21-2016, 07:57 PM

Originally Posted by FORBESAUTO

I agree 100%, what I was stating is that prop pitch change does not necessarily yield the same results as a gear ratio change. In my situation I gained more by going to a 2.0-1 gear than by going to smaller pitch prop. That's all.

gear change and pitch change same concept but really different. agree 100%