Having built plenty of successful 4 cly. Mercs over the years. I have found out that expansion chambers are not my cup of tea on deflector Merc`s. Megaphones are still somewhat of mystery, just a ton of variables that can effect performance,porting and other internal mods, how you cool the engine and pipes. I have found that the hotter you can run the engine and pipes the better the performance. I have actually melted an aluminum megaphone off with no damage to the engine. Pipe length and the angle the exhaust exits also has a lot to do with performance. Witness the McAfee sidewinder pipies on their E. Experimenting with cooling can gain you a lot, but can be expensive. The ignition that we run now has an effect.