OK, I've searched this forum and not found the answer I'm looking for (if it's here somewhere already, please redirect me). I have replaced the stock muffler on my 2003 F-150 (4.2L, auto trans) with a Flowmaster. How much (if any) more performance would I get by replacing the stock piping from the cat on back with a larger diameter? How about adding a set of headers and or going to dual exhaust? I'm trying to decide if it's worth the effort or not.

 

There was some discussion here and in the Exhaust forum about 6 years ago on this subject. Not much since.

It is my opinion (and that of many others) that just going to a larger diameter exhaust pipe can actually hurt performance. It has to do with gas flow velocity and shock wave pulses. (Gas flow can be a pretty complicated subject).

I'd suggest not doing it. I don't think you see any gains.

As far as headers, again I'd speculate not a lot of gain - but can't say with certainty. I just don't think there is much penned up performance in the 4.2 that can be let out with just making exhaust modifications.

 

That pretty much matches the opinion of my local muffler shop. I just thought I'd get some input from folks who have the same engine as I do. Thanks much, you helped save me a few hundred bucks.

 

In reply to the exhaust and header question, you would see real gains if you were to do some engine work. Some cams and heads and what not. Just stock the only thing you would change is the sound, which isn't that bad.