In a Rotary engine, the port timing is equivalent to a camshaft in a piston engine. The higher the top of the port, the later the intake or exhaust is closing, and the longer the duration. On the exhaust port, the lower the bottom is, the sooner the port opens, and the longer the duration is. On the intake, the opening is the outer side of the port – which can NOT be changed much (the corner seal needs that area) without going to a bridge port.
We are not going to get into the various pluses and minuses of the different ports here – way too much could be written on them, so we may get into that at a later time, in another section.
Porting is very time consuming, but the more you do, the faster it gets. There are definite techniques involved, that only practice will develop. This section is mainly to just help the “new to porting” by showing the tools that we consider needed, and some of the steps of the process.
|On the left is an air grinder, on the right is an electric one. The air ones are a lot cheaper, but are VERY noisy! The electric uses a flexible shaft, and has a foot control. There are other types available, but these are the ones we use. John uses nothing but the air one, and drives everybody in the shop nuts with the noise. I use the electric, mainly because I hate the noise of the air ones.|
|USE EYE AND EAR PROTECTION !!!! No joking around – the metal burrs thrown out are one of the most dangerous things around for the eyes. If you are using air, the ear protection should also be worn.|
|These are just a sampling of the bits, grinders, stones, and sandpaper rolls we use. The ones on the left are stones and rotary files. Any rotary files other than carbide are a waste of money – the extra expense pays for itself even on the first job. The stones are used between the grinders and the sandpaper to “blend” in the grinding. The sanding is used for finishing the ports. One tool (the left of the sanders) is a “split mandrel”. It’s just a bar with a slot in it. Cloth backed strips of sandpaper are inserted in the slots for sort of “flapping” the final finish. The mandrel on the right is tapered and threaded on the end. Pre-formed sandpaper rolls are screwed onto the end.|