Repower, 2 or 4 Stroke

Repower, 2 or 4 Stroke

by Conrad & Judy Kreuter

Q: Dear Boat Talk: I have been considering repowering a Mako 20 foot center console. I presently have a very tired 150HP engine. I am considering both 2 stroke and 4 stroke engines of various horsepower. Could you explain the pros and con’s of each? LK, Flanders, NY.

A: Dear LK: When repowering a boat you should first consider how you like the performance of your present boat and motor combination? Are you expecting increased speed, different cruising rpm, or decreased time to plane? By evaluating the answers to these questions, you can narrow down the horsepower rating of the new engine. In general, the newer engines of less horsepower perform as well, if not better, than the older engines they will replace. This is due to a number of factors including fuel injection vs. carburation, and 2 stroke vs. 4-stroke technology.

Let’s take a closer look at 4 stroke benefits. The first and most important factor is that the 4 stroke, by its design, does not burn oil as a process to produce power. This means that the 4 stroke does not pollute the environment since there is no smoke while operating thus meeting the stringent EPA 2006 emission requirements. The only 2 stroke engines able to meet the 2006 standard are those that are fuel injected.

Second, 4 stroke engines burn less fuel. Depending on the engine selected, fuel consumption can be as much as 50% less than your older model. You may find that a 4 stroke on your boat may give you even greater fuel savings when compared to your old 2 stroke. This means you could carry less fuel and have the same range, or greatly increase your cruising range with a full tank of fuel. Also because oil is not being added to the fuel another economic benefit will result.

Thirdly, 4 strokes are much quieter while operating. At idle, most engines are difficult to hear. At full speed, you can carry on a conversation at the helm with your fishing buddy. A typical 4 stroke operates with much less vibration as well.

Fourth, 4 stroke engines have a flatter torque curve than equivalent 2 strokes. A flat torque curve provides plenty of power throughout the entire speed range from low to high speeds and increases the overall drivability. This means less 4-stroke horsepower is required to move the rig through the water.

One disadvantage of the 4 stroke vs. 2-stroke comparison could be the weight difference. 4 stroke engines in general weigh more than 2 strokes of the same horsepower. At the HP level you require the weight difference could be over 100 pounds. To test your boat with this much added weight simply stand close to the present engine and see how far down the transom goes. It most cases however, this weight difference amounts to ½” or less of extra draft. This means your boat will still be able to selfbail with the 4 stroke on board.

Q: Dear Boat Talk: What does a battery isolator do? Can I install one myself? GB, Islip Terrace, NY.

A: Dear GB: A battery isolator is a device which allows both batteries in a dual battery system to be charged independent of the position of the battery switch, while the engine is running. Without a battery isolator, only the battery selected by the switch is being charged.

The installation is fairly straightforward and is within the skills of the average boater. Follow the manufacturer’s directions and you should be okay. The equipment will cost between $65-80 and is available through most marine parts suppliers.