What kind of sound change would i get if i change the exhaust tips to 4"

 

Should sound deeper and throatier than stock, however you may loose some back pressure.
I would suggest checking Youtube videos for sound comparisons.
What brand are you looking at getting?

 

Just the tips? No different muffler? It really wouldn't do a whole lot, maybe just a slightly deeper exhaust note. Personally though I think anything larger then a 3.5 looks funny on our cars.

 

^^ agreed, i have 3" tips that are on the fr500s, wish they were a tad larger, but then when i see pypes tips they look a bit akward

 

Here ya go. 4" tips on my Bassani axle backs. No deeper sounding than 3" or 3.5". In fact sounds very, very close to Borlas but only a bit louder and a bit nicer. And you don't lose backpressure. It's proven that axle backs on these cars do nothing but change the sound.
Fills out the bumper a lot better than the smaller ones when viewed from behind. People tend to like the look of the way these are cut and stick out, I get a lot of questions and compliments nfrom other Mustang drivers about them.

 

I herd the stock mufflers flow pretth good. Just wanted a little more sound

 

i also have 4" tips. they are MBRP deletes with a slash cut. i think these are a good looking 4" tip.
the entire axle back is polished stainless steel.
i like to clean them inside and out.
by changing just the tips you may get a slightly deeper tone, but not much.
if you want more sound, change the muffler and/or the midpipe. i recommend MBRP deletes.

 

I lost some back pressure with my single 4" Pypes Streetpro exhaust and felt a noticable change. My custom tune made up the difference!

 

You notice a "Crap; why did I spend $$ on these 4" tips" sound to your exhaust note.

 

Go get yourself a pair of Flowmasters or something, hell with the 4" tips.