Pipe size?
 

Why do people put 3" piping on mustangs without having enough horsepower to need that size piping?

They think bigger is better.

Even on the newer cars there not pushing enough HP stock to make 3" exhaust needed. Infact it could cause a loss in power.

I would say the gt500 warrants the 3inch exhaust. As for the 5.0 is say yes still. Because you can make 450 rwhp with bolt ons....

I looked it up before I believe dual 2.5" piping is good till 600 not 450 though I could be wrong.

I could be wrong to, shooting in the dark here!

Usually....3" piping is found on big trucks. I'm fairly certain you don't need 3" till your 600 or over, or have FI because FI increases the flow and volume. That isn't to say that N/A doesn't but not as much as FI would. It's something to look into and maybe a exhaust guru will reply on this post to clarify!

Dual 2.5 in pipes are good to around 475-500 hp. After that they pose a restriction. Too big of a pipe slows the exhaust gas velocity, which in turn kills any scavenging effect that is built into the system. Much the same way that too small of a pipe kills the flow rate

Ah this sounds about right. I don't see why any mustang other than the GT500's and the new GT's would have 3" exhaust. Lets be real how many people who buy even the GT's mod it enough to get that much power out of it?

You'd be surprised how easy it is to hit those numbers with a DOHC motor. My car gained 37 hp from just a tune. For some reason Ford put a very conservative tune on the Cobras

Yeah its crazy I added a few stickers and had to move up to 3" piping.

I'm talking about GT's not cobras and GT500's I just throw the cobras in the same boat as the GT500's. for cobras you guys can reach that number easily from tune,exhaust and pully swap. The SOHC GT's won't reach this without building on the engine or FI. Most people just do bolt ons.

Yes but the new GT's are 4V cars

Yes the newer ones can boarder line 475-500 with bolt ons. I forgot to put that in my post. As you can see lack of sleep is getting to me at this point.

My pipe is huge!!

Not what she said

Really its what you are aiming to do with the car. I don't know the math equation but its dependent on the piston size, compression ratio, bore size, what horsepower your aiming for at a specific rpm and it will give you your pipe diameter needed to obtain your goal I'm sure you could Google it

IME the majority of people run 2.5in piping through the exhaust and just put the bigger tips. Personally, I hate tips that big but it does help to reduce exhaust drone.

Im with you, i bought my catback specifically with the 3 inch tips to give it that sleeper exhaust look.. until you fire it up..