Oh yeah I forgot to tell you about exhaust... The 2 stroke Detroit moves a lot more air than any other engine made, watch exhaust back pressure closely as; A. The air movement allows scavenging of the cylinders to allow for clean air for the next fire cycle and if the exhaust is backed up it won't have horsepower. B. The air cools the inside of the engine as it moves through so same as above fi the air can't get out the heat builds up and causes issues.
I did a repower one time and the salesman gave me a muffler to install he got from the owner trying to save a buck. The engine had triple the backpressure when I checked it on the dyno and the engine that was rated at 350HP would only put out 250HP. Dropped the muffler and had over 350 HP.