Header pipe length???

I've got a 2-1 header that I'm making into a 2-2. Do the two pipes have to be identical length? Or can one be say 30" from the exhaust outlet and one be 24" from the outlet?

header pipe length

I'm not an automotive engineer, but logically you have two identical cylinders. Tuning manuals go into great detail to insure the twin carbs have synchronized intake. It makes sense you want the exhaust matched as well. Different pipe lengths give different back pressure.

I think this picture says it all. http://groups.msn.com/Brit-Fe-Pics/shoe ... hotoID=233 just keep hitting the next button to see them all.

Yes the pipes should be the same length. 28-30 inches is a reasonable length for a Commando.
My racer uses 25" headers, but it produces all the power up the top end. Longer ones give you more mid rabge.
If you have assymetric pipes, one cylinder will be producing less power than the other at certain rpm , I'd suggest that vibration will be the result.