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Author Topic:   Increasing Horsepower
sanjaun2 posted 06-07-2004 08:30 PM ET (US)   Profile for sanjaun2   Send Email to sanjaun2  
I have a 2004 Mercury 40 two-cycle. I noticed the bore and stroke are the same as the 50-HP. Is there a way to make my engine a 50-HP?. Is [the difference between the 40-HP and 50-HP engine] just carburetors? What is the price of the modification?
DaveS posted 06-07-2004 09:35 PM ET (US)     Profile for DaveS  Send Email to DaveS     
I once had a 30-HP Mercury outboard motor. I asked that same question about 5 years ago. The consensus was "leave well enough alone." Take into account the outboard engine industry works within a 10% margin for error when estimating its horsepower ratings. A few things to consider: if we add the 10% that is 44-HP. Even if the other outboard was right at 50-HP, would you really think the extra 6-HP would make a difference? I'm always amazed that on the Montauks I see [speeds of] 35-MPH with 50-60-HP and 40-MPH with the 90-HP. Just don't think [trying to modifiy the engine from 40-HP to 50-HP] is worth it, plus, since it's a new outboard, what would that do to your warranty?

Good luck!


jimh posted 06-08-2004 09:16 AM ET (US)     Profile for jimh  Send Email to jimh     
There are many engines which have a common displacement but are rated at different horsepower. Manufacturers always scale the pricing to match the horsepower. There is a popular notion that a less expensive, lower horsepower model of an engine could be turned into to the higher horsepower version after purchase. Unfortunately, I don't recall reading of many success stories for such conversions.

Many anecdotal reports exist of simple devices like throttle stops or flow restrictor plates which could be easily removed to yield more horsepower. Or perhaps just something really simple, like removing all the carburetors, tearing them down, replacing some components, re-installing the carburetors, re-installing the linkage, re-calibrating and synchronizing the carburetors, then finally putting the engine on a dynamometer and seeing if any real increase was obtained. Opps, better put the engine on the dynamometer, first, to get a baseline. No problem for the average outboard motor owner, I am sure.

On modern engines, it gets more difficult. The additional performance may come from code in the engine control module. The engines may be mechanically identical, and the difference in horsepower rating is obtained entirely as a result of the engine control module functions. Just buy a new control module for about $700 and you get the improved horsepower.

2manyboats posted 06-08-2004 10:33 AM ET (US)     Profile for 2manyboats  Send Email to 2manyboats     
There is a simple way to make the 40hp. into a 50hp. It does involve a trip to the Mercury dealer and will probably cost several hundred dollars, but they can do it. I would bet a Yamaha dealer could even change it to a 50hp Yamaha .

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