Ouch! Those pipes could ventilate a medium-sized Kentucky coal mine! 1 3/4" pipes would be a much better choice to keep the velocity up coming from the manifolds to help scavenge the cylinders. Your intake and exhaust system is designed for a much bigger, freer-breathing engine than the stovebolt can ever be. Try connecting a couple of 1/2" chains capable of pulling 20 tons with a short length of 2-ton capacity 1/4" chain, and you'll have approximately the same situation.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!