My TTR originally had a 1 3/4 X about 44in pipe and at 4300 RPM it would just quit revving and 8 stroke. I consulted the gurus and then made this one
2" X 34" (overall pipe length not from valve and polished stainless) and the thing absolutely came alive. The first time I opened the throttle it ran through 6K before I could even reach for the clutch to shift it and my seat of the ass dyno said a minimum of 10 more horsepower. It is running a 5X cam with 1 5/32 10tt9 and big compression. AEI mag for sparks and valve timing at 4deg BTDC on the crossover.
Sadly tho' nowhere to play with it anywhere close to me.
The pipe is made up of 3 pieces, one is a preformed standard bend, one straight section and one custom bend from the local bending shop who normally bend LARGE structural sections for industry and architectural places.
https://www.advantecglobal.com/industrial/abt/
I tacked it together with TIG and then had it all welded by the local shop that does much of the stainless piping in the local food industry. When polished out was very hard to see the joints.
I made one and welded it myself but didn't back purge as it was just to prove the pipe before I made a nice fancy one!