These are quarter wave pipes in this case Ultra thrust for these OS .25FX's. The Nelson Ultra Thrust is no longer being produced but Dub Jett of Jett engineering is still producing his versions. I think you are already using full wave pipe on one of your engines you mentioned. A full wave pipe is able to produce the magic power boost by reflecting a pulse of the exhaust surge at the end of that long tract where the pipe is constricted at the tailpipe. This reflected wave if the length of this tract is right will reach all the way back, thru the pipe and header to the exhaust port to meet and stop the fresh fuel mixture as it will follow the exhaust out during the period in all two strokes that the exdhaust and transfer ports are still open. Walla superchaging

The quarter wave pipe work on the same principle except that there is an internal track that will cause that pressure pulse to bounce four times but matchs the same distance that the full wave pipe and therefor make the magic. A quarter wave may be slightly less efficicient tnan a full wave but much smaller and easier to package.

That TT 61 with the quarter wave Ultra Thrust running 25% nitro would using APC 10x9 and even 10 x 10 would deliver somewhere between 13,500 and 14.

John