Outboard Porting Tips

Porting an outboard motor means altering the air flow through the intake or exhaust ports. By modifying the cylinder head ports on an outboard motor, the air flow can be increased and as a result increase the power that is produced by the engine. Care must be taken while modifying the porting of an outboard engine since too much air flow through the engine can actually reduce the amount of power the outboard can produce.

  1. Angle

    • When creating a new port on an outboard the angle needs to be considered. The goal should be to reduce the amount of friction that is created by the air as it enters into the outboard cylinder. The higher and straighter the port can be created into the outboard cylinder, the more power will result from the modified porting.

    Exhaust

    • The intake and the exhaust ports must be equal. The air needs to be able to flow in and out of the engine at an even rate. If the intake ports are modified to allow for greater air intake, then the exhaust ports must be modified to allow the increased air to exit the engine. Failure to do so will result in a loss of power as the engine won't create enough combustion. The modified exhaust port can be slightly smaller than the intake ports, but the angles should match the intake ports.

    Considering the Block

    • Before starting any porting modifications, it is important to consider the amount of material that is available in the engine block to support the additional porting. Boring new ports into an engine will result in compromising the strength of the engine block. A block with thick enough side walls can be modified without compromising the integrity of the block. Smaller engine blocks should not have modified porting, as the increased combustion could result in a blown piston.