Hello all, I'm new to this site and this is my first post.

First off let me say I just bought an 05 mustang 4.0 and I love it.

My question is I put a flowmaster American Thunder muffler on it and it sounds great, then yesterday installed a K&N air filter and now it seems like its shifting at higher rpms (3500-4000) and it sounds like the engine is working harder than it was before, I think it was shifting around 3000. would the new filter have anything to do with this or am I maybe just being paranoid? I only drove the car for 4 days with the new muffler before putting the filter in but I was accustomed to the sound and shifting range, now it seems as tho its changed. As long as its not straining the engine or tranny I dont mind

 

Welcome, with the new S197 cars you are going to need a tune for the parts you installed.

Sorry

 

yup, sn197's need to be tuned with a cold air intake

 

I didnt put an intake in it just a filter. I think i was being paranoid, what it boils down to is my driving habits and how much I get on it. all in all the muffler sounds great and everything seems fine. still want to get a tuner tho