Hey klick...,
I was reading through Jennings's "Two-Stroke Tuner's Handbook" and came across a couple of things I thought were pertinent to your current project (pay attention for the word "symmetry"):<blockquote>"Present motorcycle engines are all scavenged through windows in their cylinder walls, with scavenging air being supplied from their crankcases. This system is beautiful in its simplicity, but it does have serious short-comings: First, there is the relative incapacity of the crankcase as a scavenging-air pump, which prevents even the hope of having excess air to use in clearing the cylinder. Secondly, the use of the piston's motions to open and close (actually, to uncover and cover) the exhaust and transfer ports creates enormous difficulties in a number of areas related to clearing and recharging the cylinder. The low scavenging pressure available makes it absolutely essential that pressure in the cylinder be no more than slightly higher than atmospheric when the transfer ports open, which means that the exhaust phase must begin well in advance of the uncovering of transfer ports. And, because the piston-controlled exhaust timing is necessarily symmetrical, the exhaust port will remain open long after the transfer ports close -- leaving an unobstructed opportunity for the fresh charge to escape the cylinder. Indeed, the charge injected into the cylinder has every reason to escape, as the upward motion of the piston, moving to close the exhaust port and begin the effective compression stroke, is displacing the gases above its crown. Gas pressures always try to equalize, and those in the cylinder can only do that by moving back into the transfer ports, while these are still open, and out the exhaust ports. Thus, it is virtually inevitable that some portion of the fresh charge will be lost into the exhaust system, and that the upward stroke of the piston will also tend to aspirate some of the charge back down in the crankcase."
(p. 106)</blockquote><blockquote>"Perhaps the most valuable bit of information I can supply is that unless you plan to alter fairly radically the speed at which your engine makes its maximum output, there is no need to do anything beyond smoothing the casting flaws out of the transfer ports -- and even that should be approached with some caution. Why? Because in scavenging efficiency so very much depends on symmetry of flow. Get one transfer port flowing conspicuously better than its mate on the opposite cylinderwall, and while you may have improved the delivery ratio slightly, the scavenging pattern will have been upset and power output will drop. As as matter of fact, I am inclined to think that the upper reaches of the transfer passages should be left entirely alone, unless to remove some conspicuous casting defect. It is in any case extremely difficult to do precise work up near the port window, and almost impossible to raise the port's roof without altering its angle -- which is the wrong thing to be doing."
(p. 116)</blockquote><blockquote>"All present loop-scavanged motorcycle engines follow Dr. Schneurle's original pattern fairly closely, and many -- perhaps most -- are more or less exactly the same: Twin streams of incoming charge emerge from twin transfer ports flanking the exhaust port, and angle back across the piston crown and slightly upward, joining into a single stream at a point approximately two-thirds of the way back from the exhaust port. This stream is deflected upward by the rear cylinderwall, and then it sweeps up to the top of the cylinder to be directed back down the forward cylinderwall -- moving the residual exhaust gases out of the exhaust port as it advances in that direction. There is as you might expect, some turbulence generated by this activity, which is unfortunate because turbulence promotes the very kind of churning and mixing that should be avoided. But the turbulence is minimized when the flow is symmetrical, and there will therefore be less dilution of the fresh charge trapped in the cylinder at exhaust-port closing. Skewing either transfer port to one side, or lifting the upper edge of one slightly higher than the other will badly upset the scavenging pattern."
(p. 118)</blockquote>Glen
Thanks Danman1. It's guys like you that keep me having fun. Oh yeah thanks, for the spilling coriction. Dan, my saws are not the speed demons that maybe you build but they are good work saws. I do not have tons of experience building race saws, but in the last year since I started building saws for others on my own, I have not had a single saw come back under warranty. Actually I have not had one come back for any reason yet. Did I forget to mention that every saw I send out goes out with a warranty. OOPS! You ASSUME too much. You assume that I told you every little detail. I did not have time to go into it nor would I share the little things that I spent countless hours figuring out. Not to mention all the pistons and cylinders I screwed up in the learning process. I actually have a shelf in the shop of pistons and cylinders that are now junk but are of great value to me as I learned each time I did something wrong. I was only explaining the concepts of what I was trying to do. Mostly because I like to talk saws with others who like to talk saws. I also know that every one approaches a puzzle different and maybe some one has a thought I did not consider. Dan I am sure your saws will walk all over mine in a race but hey that's not what I do. An old timer once told me: An arrogant man criticizes but a confident man shares his knowledge with others. I did not take you as a big ol' mean man. I've got thick skin besides I know the end product and it makes me happy. 
