Mercury 9.9 hp 4 stroke upgrade

[newo]

Hi, I was wondering if it's possible to upgrade my 9.9hp four stroke engine to a bigfoot is this possible? And if it is, what do I need to change?
I use this auxiliary engine on a 20 foot boat mainly for trolling, maximum speed wot is 4 knots, I would like to upgrade hoping that I would be able to increase my top end speed to at least 6 knots. Any ideas if this is possible?
Thanks in advance

 

[Star]

Re: Mercury 9.9 hp 4 stroke upgrade

That is alot to ask of that little engin. what is it turning at 4 knots. The bigfoot has a lower ratio, but a 20' fiberglass is alot of boat. even if you changed the carb to make it a 15hp and a 4 blade 8 pitch prop you would be lucky to make it. Idon't think it would be worthit a new LU is about $1000 for that motor.

 

[ondarvr]

Re: Mercury 9.9 hp 4 stroke upgrade

There is no upgrade, about the only thing you can do is put a high thrust prop on it, probably won't increase your speed much, if at all, but you will have a little more thrust.

 

[Mi duckdown]

Re: Mercury 9.9 hp 4 stroke upgrade

Why do you need 6 knots as opposed to 4? although there nothing you can do to that motor, to get THAT much speed.??

 

[Star]

Re: Mercury 9.9 hp 4 stroke upgrade

Why do you need 6 knots as opposed to 4? although there nothing you can do to that motor, to get THAT much speed.??

Some troll for samon at 5 by 5'

 

[newo]

Re: Mercury 9.9 hp 4 stroke upgrade

Thank you all for your replies, guess best option is to change engine one day, didn't really want to go for that option as I didn't want to add more weight but seems to increase the speed I have no other option. Thanks again for your replies, and 6 knots is need for trolling for little tunny fish

 

[ondarvr]

Re: Mercury 9.9 hp 4 stroke upgrade

Most people don't use a kicker for Tuna, the typical 6 to 8 knot speed is just too much for a small motor. This is main motor territory.

 

[Sea Rider]

Re: Mercury 9.9 hp 4 stroke upgrade

Not an issue pushing a 20 ft boat with a 9.9 as long you have tached that engine at wot to know if engine is working inside min, max wot rpm factory stated for that model. Install an induction tach, go for a wot spin, with you alone and lightly loaded boat and check achieved max rpm on flat glassy, no wind water cond. Will know inmediately if under propped and by how much.

We push 24-26-30 footer much heavier sailboats with 9.9, 15 as long are wot rpm tested and re propped accordingly for that work, usually prop pitch play to work near max wot rpm parameters and avoid lugging engine with standard factory delivered prop.

Can't turn a 9.9 four strokes into a 15 HP, a 9.9 is 208 CC and a 15 is 351 CC, different powerheads,

Happy Boating