Converting the 4HP 4 stroke engine to 6HP

[Sheff69]

Hi,
I have a 2007 4HP mercury outboard that I would like to convert to 6 HP.

I note that the bore, stroke and weight of each are exactly the same, and it seems that only the maximum RPMs are different.

Is it possible to change the 4HP engine into a 6 HP? If so, what do I need to change?

Regards
Sheff

 

[trackerjohn]

Re: Converting the 4HP 4 stroke engine to 6HP

I was going to do the same with my 9.9 (up to 15) but was told that the intake and valves were too small. Maybe from 4 to 6 might not be to much but you will probally need at least a carburator from a 6. You need to find out if the 6 has bigger valves and intake and possibly exhaust.

 

[luv2b0at]

Re: Converting the 4HP 4 stroke engine to 6HP

I replaced the carburator on my 1999 Mariner 9.9 4 stroke due to a dunking in salt water. I replaced it with the 15 HP and it runs great. No bogging or anything and you can definitely feel the power increase. It's not a placebo. I'm not sure if it actually boosts it up to 15 HP, but I have more power than before and the $$ difference was roughly $20 between the two carbs available. The new one bolted on w/o any modifications. Definitely worth it.

 

[Sheff69]

Re: Converting the 4HP 4 stroke engine to 6HP

I was hoping that I wouldn't have to change the camshaft or the cylinder head (valves), I guessed I might have to change the carburetor. I have asked a local dealer if I could borrow (or even just look at) his parts list for the 4HP and compare it to the 6HP, but for some reason he wasn't happy about doing that.

I would have been happy for him to either sell me the parts, and I'd do all the work (I've rebuilt a number of car and motorcyle engines), or even let him do the work for me, but he still didn't appear too interested.

Maybe when he starts feeling the recession, he might want the work? Trouble is I can't wait too long, I would like to get the work done before fishing season starts in the north east.

Sheff