you guys with "big tube is better" are 100% wrong!
unless its race ONLY,
dyno testing (chassis and engine) have proven low rpm power loss (hp and torque) with big tubes,
I'm talking under 400 cu in motors,
most of you drive at under 5000rpm, so large tube is useless.
the decrease in velocity with large primary tube, decreases scavenging,
and efficiency ( unless you are at high rpm,)
plus... when you add exhaust/mufflers, you compound the issue,
limiting the free flow of exhaust .
just my 2 cents,