Don't do it yourself if you don't know...
Thanks Big B. By gas reaction you mean the combustion,
or the flows in/out after exhaust opens? (or both?)
After taking a closer look at changing timing, and calculating
areas, I noticed that in some cases (stock cylinders with very
low port timing), it's difficult to raise the exhaust port by removing
material from the top, then making it as wide as possible at the top,
and keep area down where it should be.
If max size is important, then raising the barrel (to meet intake timing)
seems to do the trick. The exhaust roof needs less grinding, giving you
a deficit of area that you can use to widen the port at the top.
PS Bounkass is paying me back for my comment on the in-cylinder
camera.. we are now even!
One way to raise the timing without making the exhaustport bigger (higher) is raising the cylinder and make it shorter at the top.
2stroke is never finished. There are a zillion ways to reach different things. That's what makes it fun
I prepare most cylinders this way by raising the cylinder to put the transfers close to the duration I prefer then cut the exhaust port.
If you go to wide on the exhaust the bottom end power will be lost.
If the port is the correct size closest to the piston then sometimes different shaping techniques can be applied to the tunnel part of the exhaust port to make the exhaust port perform more efficent .
Aloha, I have read all the previous posts here and have comments and maybe some questions...
1: I have seen that an exhaust port that is widest and flatest on the top give the strongest exhaust pulse into the expansion chamber and more power.
2: The strongest cylinders seem to have the most exhaust escaping at the top of the port, ie Evo, wide bridge port. No single rounded exhaust port will produce much power. Of you look at the carbon buildup in the exhaust port, you will find the cleanest area on the top and so the fastest exhaust escaping there.
3: My Malossi Replica with single exhaust port and two auxillary ports gives much better power than a single exhaust port because of the larger exhaust area opening. (time/area). My Metrakit sp2 is mostly the same as the Malossi Replica, but has a larger main port and much larger auxillary side ports and gives more power than Malossi.
But I think were it gets very difficult when you make the transfer angles different with larger exhaust port, you will loose the charge short circuiting into the exhaust and get less power. This is where a lot of research and development and several ruined cylinders will come into play.
frank
2stroke is never finished. There are a zillion ways to reach different things. That's what makes it fun
Your point 2 isnt correct, its because thats the first place when the mix can escape (when the piston comes down) so its quite logic that there will be allot more pressure on that little spot.
/edit nevermind your correct but what I wrote above is the explanation for that