Performance Upgrades: 4 Ways to Buy Better Speed

Not long after people get a new-to-them boat out on the water, they begin to wonder how they can make it go faster. Well, after you’ve eliminated needless weight, made the running surfaces as smooth as possible, and made sure your powerplant is in top form, you’ll probably find that better performance is directly related to the amount of money you have to spend. Don’t have a lot of greenbacks, you say? You won’t be the fastest guy on your lake. Flush with cash? Just how fast would you like to go, sir?

Here are four things you can do to your boat—without disassembling the engine—ranging from inexpensive modifications that produce modest gains to more pricey options that provide greater performance.

Custom Marine exhaust header

Smooth steel exhaust headers like this one from Custom Marine can add significant top-end speed.

1. Tune your Propeller

As this process has become more popular, propeller tuning shops are popping up around the country. Mercury Racing in Fond du Lac, Wisc., offers “lab finishing” on its propeller models. Other shops such as Throttle Up Propellers in St. Petersburg, Fla., or Hill Marine in Santa Ana, Calif., also can tune a stainless propeller for your application. Depending on your needs, a competent propeller shop can help you get the most from a stainless propeller. They can tune for better planing, turning, and, of course, more top speed. Costs can run anywhere from $200 to $500. Double that if you have twin engines.

2. Add an Exhaust Header

Stock exhaust manifolds don’t provide the smooth, tuned cylinder evacuation of a tubular steel header, which can net you as much as 30 to 40 horsepower on big-block engines. Factory manifolds on the MerCruiser 496 Mag and 496 Mag HO engines flow pretty well, but not nearly as well as tubular steel headers. The horsepower advantage should net you anywhere up to 4 mph on the top end. The catch? There is no such thing as a cheap marine header. A good tubular stainless-steel header system is going to cost you around $4,000 just for parts. Then there is labor. You also might need to buy a higher pitch propeller. For more information, visit Custom Marine, Stellings Marine Products, and Lightning Performance Marine.


Competent specialists (like the Mercury Racing techs shown here) can tune a propeller for optimum speed. Photo: Mercury Racing

3. Advance Your Timing

Some folks think that by filling their fuel tank with high-octane gasoline, their boat will go faster. No, but what high-octane fuel will allow you to do—if your engine-management system permits—is advance the ignition timing without fear of pre-ignition knock. Advancing the timing will give you a small boost in power and perhaps a mph or two on the top end. The downside is that as long as you keep the timing advanced, you will have to run the high-octane stuff, which increases the price of a fill-up. Ask your mechanic if your boat is a good candidate for the modification. Cost is nominal, probably about a half-hour labor charge, plus the price of high-octane fuel.

4. Add a Supercharger

If you want big gains without tearing down your engine, adding a supercharger is the way to go. Depending on your boat, its engine, and your needs, you can get anywhere from 10 to 25 mph more on the top end. Manufacturers that specialize in marine applications include ProCharger, Vortech and Whipple. The Whipple system requires you to remove and replace the stock intake manifold. The Vortech and ProCharger models do not. Regardless of the supercharger you choose, you might need to burn premium fuel and alter your ignition timing. Headers would help, too. You most definitely will need a new propeller to get the most from all that added power. Superchargers start at around $3,000 and range as high as $8,000 depending on your application. Then you have to add in the price of labor if you don’t perform the work yourself. We told you performance doesn’t come cheap.

Brett Becker


  1. kevin ardent says:

    I have a 2006 496 mag ho I’ve been told if i have the computer remapped for 91 octane or better along with after market exhaust . I could see an horse power gain of 50 hp ? is this true

  2. Outlaw Speed says:

    Unfortunately not.. You will be lucky to see 15/18

  3. Brad Barclay says:

    I was told by Mercruiser that a turbo charger would add heat and detonation problems to my twin 496’s. He says there is very little that can be done to these engines without decreasing their reliability. I wonder if he is being too conservative?
    I like your recommendation for tubular headers… If I add 4 MPH, will I see a decrease in fuel economy?
    Will I need to change the computerized fuel mapping at all? Will I see a decrease in reliability?
    Thanks for the help!