headers vs manifolds on a 318 2bbl difference ????

The 360 in my D200 got a noticeable boost in throttle response and part-throttle acceleration going from manifolds to 1-5/8" Hedman long tubes. Originally a 2-bbl engine, I swapped on a Performer intake and 1406 carb (along with MSD-style ignition). When I put in the headers I ran 3" pipes (same diameter as header collectors) as far back as I could before connecting back to the factory exhaust. You barely need to touch the gas pedal to get that 4500-lb beast moving, it's pretty amazing. Something I've always found interesting, the engineers knew about the benefits of free-flowing exhaust in HD truck applications for a long time as mine has 2-1/4" true duals that look like to be factory and it's a 1972 3/4-ton pickup. Same goes for newer 3/4- and 1-ton trucks with gas V-8s, sometimes they run dual head pipes back to the middle of the frame or farther into a BIG 2-into-1 muffler and a fairly big tailpipe.