NEW 340 manifolds at a reasonable price
I have ran a 13.2 @105mph with my 340, 4 speed, 3.91 gears and E70-14s, through the stock manifolds.
This was on a questionable clutch. Im sure I could get into the high 12s.
Don't know what the limit for the manifolds (unmodified) is, but my guess is that I'm getting close.