Porting or tuning is a metal machining process performed to the cylinder ports (exhaust transfers) that alters the timing, area size, and angles of the ports in order to adjust the power band to better suit the riders demands.

Please report any bugsissues in this Forum Feedback Help thread.

A myriad of different aftermarket accessories is available for you to custom tune your bike to better suit your needs.

The most common mistake is to choose the wrong combination of engine components, making the engine run worse than stock.

Use this as a guide to inform yourself on how changes in engine components can alter the power band of bikes engine.

Use the guide at the end of the chapter to map out your strategy for changing engine components to create the perfect power band.

That is how a two-stroke engine completes a power cycle in only 360 degrees of crankshaft rotation compared to a four-stroke engine which requires 720 degrees of crankshaft rotation to complete one power cycle.

These four drawings give an explanation of how a two-stroke engine works.

This pressurizes the crankcase causing the reed valve to close.

At about 90 degrees after TDC the exhaust port opens ending the power stroke.

A pressure wave of hot expanding gasses flows down the exhaust pipe.

The blow-down phase has started and will end when the transfer ports open.

The pressure in the cylinder must blow-down to below the pressure in the crankcase in order for the unburned mixture gasses to flow out the transfer ports during the scavenging phase.

Meaning that the unburned mixture gasses are flowing out of the transfers and merging together to form a loop.

The gasses travel up the backside of the cylinder and loops around in the cylinder head to scavenge out the burnt mixture gasses from the previous power stroke.

It is critical that the burnt gasses are scavenged from the combustion chamber, in order to make room for as much unburned gasses as possible.

The more unburned gasses you can squeeze into the combustion chamber, the more the engine will produce.

Now the loop of unburned mixture gasses have travelled into the exhaust pipes header section.

The gasses arent lost because a compression pressure wave has reflected from the end of the exhaust pipe, to pack the unburned gasses back into the cylinder before the piston closes off the port.

This is the unique super-charging effect of two-stroke engines.

The main advantage of two-stroke engines is that they can combust more volume of fuelair mixture than the swept volume of the engine.

Example: A 125cc four-stroke engine combusts about 110cc of FA gasses but a 125cc two-stroke engine combusts about 180cc of FA gasses.

The compression wave reflected from the exhaust pipe is packing the unburned gasses back in through the exhaust port as the piston closes off the port the start the compression phase.

In the crankcase the pressure is below atmospheric producing a vacuum and a fresh charge of unburned mixture gasses is flowing through the reed valve into the crankcase.

2 Stroke Tuning Software