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Question on gear ratio
Hello guys.. My boat is a Crownline 210 ccr cuddy 1994. When I bought it, it had inside a mercruiser 4.3 carb with alpha 1 gen 2 gear ration 1.81. I have put now a mercruiser 5.0 carb and have left the 1.81 gear. Now the prop I have is a Mirage plus 23p, WOT is 4400 and the top speed is 34mph, while the cruise speed at 3200rpm is 24mph.. My question is... would it be better if i’d put gear ratio 1.61? Thank you very much for your thoughts. |
No, it will lower rpms and lug the engine. You should even probably drop to a 21" Mirage plus and get the rpms up to about 4800
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Question on gear ratio
But if i put 1.61, prop should spin faster and i drop down to 21p or 19p And i will get maybe the same cruise speed but better hole shot? I don’t care about top speed, I just want to have a decent cruise speed |
It is rob Peter to pay Paul, Merc only recommends changing gear ratio when out of available prop pitch...and there is plenty of room to move up.
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Ok! Everything is clear. I need a bigger engine like 5.7!😂 Thank you guys |
Based on a boat weight of 3900lb, people gear of 500lbs and 20 gallons of fuel the merc prop selector for a 1:81/ 5L combo is a 19P Rev 4, and 21 on Vengeance, B. Max and inertia.
1:61 drops pitch to 17,18 and 19P depending on the prop design Griff hits it again. |
Ok I will try 21P to see if this works better, otherwise I’ll leave the current set up: 1:81 prop 23P RPM 4400 with four people on board and I guess that’s the best I can get. |
you will likely find you gain rpm and the boat actually runs faster - in other words, your current "set-up" hit a wall - its' maxed out for what it can do...Prop design, pitch and diameter will play into your performance as well....
https://www.mercurymarine.com/en/us/...or/#!/step-one |
Great link, thank you! I tries but I end up with a range of suitable props that go from 15p to 25p. But I guess I could not go anywhere with 15 as well as with 25. is there something I have not understood properly or the selector is actually always proposing such a wide choice? |
Originally Posted by Griff
(Post 4700548)
No, it will lower rpms and lug the engine. You should even probably drop to a 21" Mirage plus and get the rpms up to about 4800
Originally Posted by Constantin911
(Post 4700704)
Ok I will try 21P to see if this works better, otherwise I’ll leave the current set up: 1:81 prop 23P RPM 4400 with four people on board and I guess that’s the best I can get. |
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