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Potter On Performance: Time to Supercharge?

We’re often asked, “How much power can I get out of my engine”? To best answer this query, we first need to ask a few questions of our own, starting with:

1. What brand and model of boat do you have?
2. What is your current engine make and model?
3. What drive is on your boat and what are your expectations?

These are important questions, and in some cases they can prevent someone from putting too much power in their boat. Not all hulls or drives are designed for high speeds.

Once we have a complete understanding of our customers’ needs we can give them some options with various price points. Let’s face it, there’s no substitute for cubic inches. The larger the engines displacement, the easier it is to produce more power and torque.

It is important to keep in mind that a marine engine needs to be able to idle at a reasonable RPM for proper shifting. Too much idle speed can cause damage to the out-drive or transmission, depending on the application.

This is why many engine builders from the automotive racing industry have difficulty building high-performance marine engines. In the automotive world you either have a clutch or a stall-type converter, which allows for unrestricted idle RPM and large camshaft profiles. These large camshaft profiles simply don’t work in the marine word.

One of the other issues associated with these types of camshafts is water reversion. This is due to the overlap or time when the intake and exhaust valves are open at the same time. For these reasons, there are limitations to how much power can reasonably be obtained from a naturally aspirated engine. When we feel the power needed is more than can be achieved with reasonable upgrades, then supercharging is an option.

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A number of questions need to be answered before you should supercharge your naturally aspirated engine (click image for full frame).

One of the most important issues to determine when considering a supercharger is hatch clearance. A measurement from the crankshaft centerline to the underside of the hatch will be needed to make sure there is enough room for not only the supercharger package but an intercooler as well (if required).

One of the upsides to supercharging is you don’t always need to upgrade your exhaust. Unlike a naturally aspirated engine, which uses the exhaust system to help scavenge or pull spent combustion from the engine, a supercharged engine doesn’t rely on scavenging. This is due to the pressure created on the intake side of the engine by the supercharger.

A naturally aspirated engine relies on the suction created by the pistons on the downstroke when the intake valve is open to draw in air and fuel. On the exhaust stroke, the piston forces out spent combustion.

Sometimes people ask me if they can just “bolt on” a supercharger kit. I know there are a lot of packages available out there that are supposed to be “bolt-on ready.” But the installation should be done by an experienced marine engine builder. In our opinion, if an engine was not designed to be supercharged, it needs to be upgraded to handle the added stresses created by the increased cylinder pressures and loads put on the valve train. Power increases are mainly limited by the fuel octane you want to run.

Today’s superchargers are very well built and far better engineered than the ones we saw back in the ’80s. Bottom line: If the power you want cannot be achieved reasonably from upgrading your naturally aspirated engine and your engine is a viable candidate, then supercharging is the way to go.

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