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Mercruiser Swapping gears because its cheap

aaronp

New member
Recently I had purchased my 1989 ebko Monto Carlo with the 3.7 Merc. It was awful getting it to run right. Well my problems continued. I finally had the motor perfectly dialed in. Well long story short I was doing a speed test run. I ran up and down the river as Im unfamilar with these particular waters. I checked depth with my eyes and depth finder. Long story short at 40 mph In the middle of the river i hit a large rock formation. The lower unit cas
ing, prop was obliterated. It popped out of gear, and destroyed the upper gears. Heres what I have. 3.7 Mercruiser 165 horsepower 40 mph at 4000 rpm. 1.81 gears. I noticed a bit of issue getting it to plane. i wasnt spending 1700 for a new lower and upper. Solution =I picked up another aplha one gen one setup for 200$ Problem=Different gear ratio.
My boat 3.7 merc 165 hp 4000rpm 40mph 1.81 gears
boat it came off=3.0 merc 130 hp 3700rpm 1.94 gears, or a number very close
at 35 to 40 mph 21p prop.
It does mount. Will it work? Will I be able to plane? Both boats are 18.5 foot cuddy style with similar haul structure and weight. The big difference is horsepower, and rpm. What prop should I run.
 
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Recently I had purchased my 1989 ebko Monto Carlo with the 3.7 Merc. It was awful getting it to run right. Well my problems continued. I finally had the motor perfectly dialed in. Well long story short I was doing a speed test run. I ran up and down the river as Im unfamilar with these particular waters. I checked depth with my eyes and depth finder. Long story short at 40 mph In the middle of the river i hit a large rock formation. The lower unit cas
ing, prop was obliterated. It popped out of gear, and destroyed the upper gears. Heres what I have. 3.7 Mercruiser 165 horsepower 40 mph at 4000 rpm. 1.81 gears. I noticed a bit of issue getting it to plane. i wasnt spending 1700 for a new lower and upper. Solution =I picked up another aplha one gen one setup for 200$ Problem=Different gear ratio.
My boat 3.7 merc 165 hp 4000rpm 40mph 1.81 gears
boat it came off=3.0 merc 130 hp 3700rpm 1.94 gears, or a number very close
at 35 to 40 mph 21p prop.
It does mount. Will it work? Will I be able to plane? Both boats are 18.5 foot cuddy style with similar haul structure and weight. The big difference is horsepower, and rpm. What prop should I run.

There is no direct answer for this. Install a prop and take it for a ride. You will know which way to go with the prop after your test. Remember, you are going to Prop the boat for max RPM not Max speed. Max rpm should fall between 4200/4600
 
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