I've run canisters on every gas engine I've had in the air for the last 4 years. After the 1st set it was impossible to go back to exhaust diverters. Until recently I had not played around very much trying to tweak and peak an engines output, but had just gone with the recommended setup and left it at that. While playing with the BME 110 Xtreme, though, I found that all the "rules" for making power could be forgotten if you just tweaked a setup and decided to be happy with the end result. My "headers" are exactly 2.5" long on my 110's, but I also feed the exhaust into extremely oversized "75" cc Pefa canisters designed for the 3W150's. This picks up about 200 rpm over "stock" but is still very smooth in the midrange and at idle, but REAL "tuned" length for the BME can only be achieved with a much more "engineered" exhaust design. The "hot" Setup for the 3W106's, as per Gerhard, is a 7" header into the "70cc" canisters meant for the 3W140's.

If you are looking to make only top end power, a true "tuned pipe" is the only way to go. .this works great for Pylon racing, and not much else, because it will kill your midrange throttle and you will have a lightswitch for a throttle .. on or off, and not much between.

Best bet, if you want a good running engine without being "peaky" is to order an oversized canister exhaust for it (by 10-15% of the canisters rating. . they tend to be a bit optimistic, so going larger is a good idea) , and an overly long header, then put the engine on the test stand, and start slicing off an inch of the header at a time till you get your rpm peak. Be sure to adjust the mixture as the exhaust scavenging characteristics change with the different exhaust flow characteristics. The canister style muffler will keep the max power from being "peaky" but you should realize a substantial power boost as the flow characteristics become mildly optimized.