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Specializing
in used
4 stroke outboards and 2 stroke outboard boat motors.
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Modifying and Converting Outboard Motors
Looking for an Outboard Motor For Sale? Visit smalloutboards.com
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Specializing
in used
4 stroke outboards and 2 stroke outboard boat motors.
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The following article is of the opinions and statements of AFA Marine www.smalloutboards.com. We do not take any responsibility for the content on this page. The content found on this page is a perspective of our views on "Modifying Outboards". We are merely stating how we feel about this topic. We encourage and endorse all consumers and readers of this page to formulate their own purchasing decisions based on due diligence, research, and various perspectives related.
So you just bought that 9.9hp Outboard and you want to make it a 15hp. You have heard throughout the years "the only thing that is different between a 9.9hp outboard and a 15hp is carburetion. This for the most part is true but there are some other differences that may make the conversion more entailed. Sometimes the conversion is more difficult than people realize.
Why do outboard manufacturers make 9.9hp and 15hp outboards from the same mold? There are many reasons for this but the one main reason that AFA Marine feels is because of "Economies of Scale". This means that it is cost effective for manufacturers to produce outboard engines of close horsepower ranges from the same framework. If an increase in horsepower can be achieved with subtle differences than it is logical to make the engines similar with identical components. It would not be feasible for manufactures to create a different mold for every horsepower.
Below you can see two examples of how 9.9hp and 15hp outboards from Mercury and Evinrude have visual similarities. The differences occur on parts of the engine which are not as noticeable.
For almost every manufacturer the chasis, powerhead, bore/stroke, pistons, weight, cosmetic components, props, and housings are the same for 9.9hp and 15hp outboards. What separates the two types of motors lie within the fuel systems, manifolds, cam shafts, and exhaust tubes. Some of the older outboards you might have been able to get higher performance by just swapping the carburetor or jets. For the most part this is not enough. Outboard manufacturers make outboard engines tuned to a particular horsepower. If you risk swapping components with the expectations of gaining more speed you may be pushing your engine too hard. This can be a result of neglecting the exhaust or intake manifolds when converting your outboard. You have to account for all the details or you will do serious damage to your outboard.
As a golden rule in outboard motors IT IS NEVER WISE TO CUSTOMIZED OR MODIFY YOUR OUTBOARD MOTOR FOR THE SAKE OF SPEED. This comes from the advice of outboard motor manufacturers. AFA Marine supports this and we feel that the Idea is foolish and the gains are not worth the risk.
Why do outboard motor manufacturers make a 9.9hp outboard and not just a 10hp? There are many reasons for this but two stand out as being most the recognizable. 1) Many lakes require boats to have motors less than 10hp. In order for boaters to have the highest possible horsepower rating while staying under the limit manufacturers produce a 9.9hp. 2) In some states a title is not required for outboard motors under 10 hp. With this in mind manufacturers make 9.9hp giving boaters the freedom to use their engine without a title.
Why do people do this? The main reason is to gain that extra push or speed...............in actuality there is never a huge difference between the outboards(based on our tests). You will notice some more power with a 15hp over a 9.9hp but not enough to risk damaging or voiding the warranty of your outboard. If you are really keen on gaining the extra power, AFA Marine suggests purchasing a 15hp outboard. This is the wisest decision since you will save yourself the risk of modifications.
We test many 9.9hp and 15 hp outboard motors on our test boat. We do experience some power differences between the two engines but not enough to risk damaging the outboard. We hear it all the time from boaters who are forced to use 9.9hp outboard or less at their local fishing lakes. This motivates them to modify their 9.9hp to a 15hp. If you do decide to do this, which we suggest highly against, have your local certified outboard dealer do it. Do not attempt to mofify an outboard motor if you are not experienced in the total mechanics of an engine.
The following article is of the opinions and statements of AFA Marine www.smalloutboards.com. We do not take any responsibility for the content on this page. The content found on this page is a perspective of our views on "Modifying Outboards". We are merely stating how we feel about this topic. We encourage and endorse all consumers and readers of this page to formulate their own purchasing decisions based on due diligence, research, and various perspectives related.
