ORIGINAL: cmoulder
You are right, we don't want to run shorter than 27 1/8'' plug to baffle. Longer is okay (don't know yet how much longer is tolerable).
In that case, I may try 27-1/4''.
Out of town for work this week. Won't be able to get back to it again until next Monday, if then. Having some remodeling done in the house after that as well, so it will have to take a back burner for a while.
I ran some more bench tests using the 18x12, trying to remove the slight jumpiness at 1/3 throttle. Also managed to take rpm readings.
Determined that the low needle was slightly rich. Leaned it about 1/16 turn and now the LOW needle is just under 1 1/2 turns open. The HI needle was not touched and still is at 2 1/8-2 3/16 open. Stretched the pipe by 3/8" and that, combined with leaner low end, eliminated the jumpiness at 1/3 throttle.
Making the pipe length measurement more convenient for myself, the distance from the plug CL to the end of the pipe (not including the stinger) is 33 1/2" straight line. That's approximately 27 1/2" plug to baffle.
Top end rpm is higher than my ear perceived originally...I tached it at 8200 after the changes. Pretty terrific!! Throttle response is now about as linear as anything I've played with before and with the amount of output available from this powerplant, the 10 pound Aesthesis will fly in style.
Can't hardly wait for spring....back to shoveling snow...sigh!!
Matt