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165 hp top speed

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bighands5

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I have a sylvan 1987 4 cl 165

I have a sylvan 1987 4 cl 165 inboard outboard bowrider I would like to know what is the top speed this boat can go and how far should I run the rpm's with a 13 3/4 x 21 pitch.I just purchased this prop and I'm still not too happy with the speed i get out of this boat.Is this what it is and live with it or can i make another adjustment.My top speed right now is 35 to 38
 
WOT RPM range is 3900 to 4300.

WOT RPM range is 3900 to 4300.

What RPM/speed does the engine get up to?

What does the boat weigh?
 
the rpms gets up 4200 i try no

the rpms gets up 4200 i try not to push it its an old boat but i like to cruise at 3900 4000 this boat weighs 2000 lbs loaded its just i feel like I should be going alittle faster on open water.
 
Do you know what your gear rat

Do you know what your gear ratio is in your outdrive? What type of prop is the 21p you got? and what did you have before?
 
"do you mean an Alpha 1, 1.98:

"do you mean an Alpha 1, 1.98:1 Ratio?

You can go with a 23p but coming out of the hole will take longer, and will only gain about 3-5mph for top speed. Maybe the engine is tired, have you done a compression test ? Carb rebuild, tune-up ?

I'm not a prop expert but recommend trying a Piranha Propeller, I've had great results and so has a few others who I know that has tried them. Maybe think about a 4 blade prop especially if you tow skiers or tubers."
 
I think the 165 - 190 hp range

I think the 165 - 190 hp range should have a 1:81 or 1:84 Alpha ratio shouldn't it? That's what my 170hp 470 has for a leg ratio and I can do 42 top speed with a similar weight boat and a 14" x 21P prop.

I used to have a webpage saved that showed HP ratings by model number to gear ratios. Maybe somebody else can post it?
 
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