Great- I'll try that length. Can I open it up to 2 1/2 right at the Y, and finish through the muffler at that diameter? Or should the back of the Y stay a smaller diameter for any length?
Great- I'll try that length. Can I open it up to 2 1/2 right at the Y, and finish through the muffler at that diameter? Or should the back of the Y stay a smaller diameter for any length?
The sharp discontinuity in section at the merge provides all of the change you need to reflect a signal back down the secondary. The airflow, however, does NOT want any constriction, so, the way I make them is to let the 1.5 tubes come together over a fairly long joint (maybe 3x dia) to a point where the cross-section of the two pipes is equal to the diameter of the rest of the system, then cut the merged joint at the point and weld on the first section of the rest of the tailpipe. No reduction in diameter (which means mandrel bends if you are really serious).
Just one other note: as the pipe diameter goes up (and thus muffler diameter), it gets increasingly hard to shut up the noise. For four bangers, some people may find that offensive (whereas I find fives and sizes positively musical - my wife does not, however, share that sentiment causing the odd bit of marital stress).