I just finished rebuilding a 49 Plymouth, has the flat head engine. I've noticed running around 55-60 the engine sounds like its turning to high rpm's. the gent I bought it from came by to take a look and he pointed out that he had replaced the stock fan with the 5 blade thats on it now. after he left it hit me, could this be the reason it sounds like its turning to high. the stock fan is a odd looking 4 blade, I say odd because the blades are not opposite each other but have a slant look to them. could this change in fans be causing this or is it I'm not use to hearing a flat head 6 running 55--60mph on the highway--------thanks, Richie