How to Make the Most Powerfull Two Stroke - P1 Porting

While waiting for parts necessary to continue with the new engine..
Lots of comments asking why I think it will be the most powerful ever, it's time to explain the theory in detail, I'll try to lay it out as a how-to.

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First the exhaust port and duct.
It's simple compared to the transfers, The goal is to maximize port area and flow through the duct.
There's a few constraints you have to work within for an exhaust port to work.

- Width of a single port can't be too wide without snagging the piston ring, max is proportional to bore diameter, port shape(flat top less forgiving vs radiused, radiused corners.),and ring properties.
An old rule of thumb is around 70%, but you can go wider on smaller bores/not so wide on larger. To circumvent this there's twin, tripple, and even quadruple ports. Going past 100% of bore width has proven to loose power because it disturbes the scavenging, the dance between transfers and exhaust.

- Height, can't be too high otherwise you'll screw up resonance in the pipe.
I'll talk more in detail about this when we get to that pipe. In short, when the port opens a pressure wave starts traveling down the pipe, gets reflected by the convergent cone, and starts traveling back towards the port. We want this to return as the piston is about to close the port to effectively close it earlier and push fresh charge sitting in the duct back in. We also want a portion of this wave to hit when the port is closed and be reflected back. This reminder of the first wave will join forces with the next wave as the port opens again and strengthen it slightly. This then repeats for the next cycle, and the next, and so on and so forth. Resonance.
About 190deg port duration is optimum for resonance, part because the real wave doesn't start traveling until a few degrees after the port is initially opened, part because you want the wave to be a little late on the return for parts of it to be reflected back.
You should make the port high than 190deg tho, I'll get to why soon.

Don't make the port too close to transfers, will cause short circuiting,fresh charge going straight out the exhaust.

My cylinders exhaust port
- First thing you'll notice is that it's definitely breaking the single port rule of thumb for safe width, it's at 100% bore width. Why no bridges is simple, bridges reduce effective area and cause turbulence and skin friction. I'm running a special retained ring/custom piston combo, we'll get to that in another episode. The sole reason for this width is to maximize blowdown area, the area of the port above the transfer roof height, the part that's open before the transfers are uncovered.
This is what's important, the rest of the port is not, in fact in my design I've raised the exhaust port floor to almost transfer roof height. This serves a dual purpose, keeps velocity high in the duct, and reduces short circuiting from the A transfers.

Port duration is 198deg, there's a relatively large bevel on the almost flat top edge bringing it up to about 204deg effectively.
The flat top to maximize area, the bevel to increase flow, and make life easier for the ring. The reason for exhaust duration above what's best for resonance is to gain more time area,to allow the engine to rev higher - as long as the loss in torque is less than what you gain by rpm you'll increase power.

The duct.
The duct is shaped to maximize flow and keep velocity high. Three important features.
- Bulges. Spent gases don't just intuitively want to exit the cylinder at the direction of the pipe, they want to get out as fast as possible, radially straight out. The bulges are there to gently persuade them in the right direction, a "straight out" port might make them upset, have them spend more energy on their exit.
- The duct exit is smaller than the effective area of the port, about 75%, This to keep duct velocity high, about mach0.8 at the exit.
- Very high exhaust floor, promoting blowdown flow, low volume keeping velocity high.

Between the pipe and duct exit there's a short transition piece.
This quickly brings the smaller duct exit out to the header diameter which is 100% of effective port area.
This steep transition because in the pipe we want high pressure/low velocity vs. in the duct where we want high velocity/low pressure.

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