ok, i am cold too and i was thinking about how i want to spend my money this winter. I am thinking Cycle Shak 2-1 pipe for the ultra. I have the jugs bored out to 95" and the heads have been done. it has a set of Andrews cams in her and currently has true duals on the bike. Do you think a 2-1 would be a good investment or just stay with the duals and get some shinney new mufflers and shut the fuck up? oh yes, i need a new windshield...

"Conventional wisdom" says that a two-into-one provides better flow due to scavenging. That is, the exhaust by one cylinder helps draw fresh air and fuel into the other. Valve overlap keeps the exhaust valve open a bit when fresh air is drawn in, and as one cylinder fills, the exhaust from the other creates 'draw.'

If you have longer duration cams this fill supposedly is more complete. The whole process is part of "volumetric efficiency."

Now, that theory dates to the carburetor era. The time of bob-weight advances, and magnetos firing through coils from a 1935 Ford--which were in fact better.

Now, is this older technology still valid with modern bump-sticks, EFI and super-tuners? My dyno sheet says I make lots more horsepower than a shovel using every trick in the book and gasping for breath. YMMV.

"volumetric efficiency."?????
You trying to give me a headache with these big words?
I ride a motorcycle and turn wrenches. I had to look up what you were talking about.
spending 500+ dollars on a different headder just to have my cylinder sucked just does not sound
like something i should do. My riding style these days would lead me to the fact that i don't need it.
Looks like shiney new mufflers for me.... blew a speaker over the weekend. Good time for Hog Tunes and a new amp!!

Yup, volumetric efficiency. All the buzz--in 1971. It's when bikers started to learn what actually happened when buying new bumpsticks. They would buy the wildest cams, the biggest carburetors and outfit the engine with the goofiest straight pipes and then have less horsepower.

Bikes have "engine management" now. Teeny little computers that geek your bike to the perfect mix of fuel, air and back-pressure. Still the same idea. Draw in the perfect blend of fuel:air, leave the exhaust valve open 'just enough' and make sure the exhaling cylinder creates a draft for the inhaling cylinder--but not too much lest you suck all of the good air right out the pipe.

All that to learn that "mild not wild" makes the most power. Simple, right?