My son has a 04 Mustang V6 3.9L. He wants to replace the the exhaust system, so I have been trying to help him. At Planet Magnaflow I found a system P/N 15717 that indicates it is for the 04 V6 3.8L. My question is this, do any of you know if the 3.8L and the 3.9L systems are interchangeable? I do not know what the differences between these two motors are and do not want him to order something that will not fit and then have to pay a restock charge to return it.

Thanks for your help,
Lon

 

There's exactly the same.

 

Thanks for the response. I called MagnaFlow directly and they told me that it was designed for the 3.8L and would not work on the 3.9L.
I was also under the impression that the application would fit either engine.

 

Not sure quite what they were thinking. The 3.9 40th ann uses the same scheme as the previous 6ers. And just about anything can be made to work at a shop...

 

they are the exact same motor. the exhaust will fit no problem. magnaflow don't know what they are talking about.

 

Who ever you were talking to was proably reading from a computer screen rather than using actual knowledge. The exhaust system will work.

 

Well we went ahead and purchased the Magnaflow exhaust kit. It installed just fine.
Another quick question. My son now wants to add a CAI and has been looking at the BBK. Again it is listed only for the 3.8L and not the 3.9L. Is there any difference at this end of of the engine that would prevent its installation?
Also I am wondering if the 2004 requires anything else, like a tune, after adding the CAI.

Thanks,
Lon

 

just order the CAI off of american muscle, it is the same as the BBK without the mark up and with out the logo. A CAI won't do much, so I honestly would try and talk him out of it. It cleans up the engine bay look a bit but that is all it does on the V6's. BTW the one on American Muscle says 99-03 or whatever, but it will also fit the 04.

Try and talk him into a set of Underdrive pulleys, a handheld tuner, or if the car is a 5spd a short shifter.

Since it doesn't sound like you want to spend a whole lot yet, maybe start saving/thinking about getting a set of gears. They will really give the car a nice bump in acceleration.
With gears though you need the gears, a rear end rebuild kit, a t-lock(might as well since the rear end is open and apart), a tune(to recalibrate the speedomoter) and the install( not something most have the ability to do).

 

+1 on the gears

 

+2 for gears, and for the whole CAI thing just take out the air silencer and had a pretty noticeable difference nothing major but will pretty much do the same as the CAI