I am planning to install a Flowmaster cat back sys. on my 150. What I am wondering is, do I need to, or can I get away with muffler only? If I do go with the cat back sys, will I have any problems with "blow back"?

 

just changing the muffler is fine,but it sounds better if you get a single in dual out muffler.you don't have to buy a cat back system you can get a muffler shop to do it for less than what that'll costand as far as blow back i don't know what you're talkin about

 

I was told that if I go to a 3" exhaust from a 2 1/4", my new pipes will alow air to flow back up into the exhaust man. This could cause major problems. Will the flowmaster do as it says and give me more horse and better fuel mileage, or is it just going to sound better?

 

Yes, a muffler only exchange is a great upgrade. You'll get increased HP, the sound of choice, keep your factory SS pipes, and spend little money. Your factory pipe is 2.5", not 2.25". Whoever gave you "blow back" advice was probably speaking of backpressure. If you buy a pre-engineered cat-back, you will also be fine. The guesswork is removed and they're properly designed to perform well.