[car4jim]

Your dealing with a pressure drop analysis of your fuel system. The total pressure drop with 3/8" will be higher than 1/2", but not much. I don't think you will notice any difference. If you are getting at least 7 psig fuel pressure to your carb at full throttle, your Gold! If anyone can calculate the max fuel flow required for 500 HP and 600 HP engines, I will do the tradestudy to see what the pressure drop difference is for each size line.