Please enlighten me wise ones of TMS. My new to me 07 GT had axlebacks when I bought it. Pypes muffler deletes. I will say they sound better after a tune. But not really my cup of tea. One thing I am missing relative to previous cars is a nice decel burble. Granted my first auto stang but i long time ago I had an 02 tbird. even that thing had a decel burble it was auto of course. Is this common for these pipes or PYpes as the case may be. I had an o7 stick previously and JBA axlebacks hey had a decel burble.
Secondly, now I have just straight tubes coming back. It appears stock to where the axlebacks would meet the exhaust pipes. of course the person before had the axlebacks welded on. Anyway, on the the point made in the header I assume that these significantly reduce backpressure compared to the stock mufflers. 1. is my assumption correct. 2. what effect does this have on performance. 3. would a muffler setup be better?
Thank you.

 

As I recall, Ford engineers spent a bit of time and effort in minimizing back pressure and to get the right sound as "sound sells" a lot. I recall some article concerning testing and the claim that the OEMs will support something like 450 hp but I don't have any link or solid info on that.


The auto and manual GTs got different part numbers, but I have never seen inside a auto muffler to see if it's much different than the manual mufflers. Our '08 has OEM manual mufflers but I picked set of long stored never used auto mufflers to try after I heard they sounded great on a manual. I've been happy with OEM though and haven't tried them yet.

 

Adding mufflers will quiet or eliminate any popping or burble so if you want that sound do not add any restriction on your exhaust. When you decel your mixture leans out and flame propagation is slower causing unburnt fuel into your exhaust. That is the burble or pop. Adding back pressure will lessen the amount getting into your exhaust. My car rumbles pretty darn loud when I decel but my upshift and downshift points are set real high. The higher the rpm when decelerating the more burble you will get. I suspect you have a stock tranny tune so it is never going to be in a shorter gear while decelerating so you wont get that.

 

I get a nice burble with my GT 500 quads if I use selectshift and downshift manually from a higher speed. Sport mode also has better up/downshift points. Not an option on the '07, but a tune that changes the shift points might help.

 

I'm really not sure if the lack of backpressure causes the burble, or if the straight-through mufflers just let you hear it more. The factory exhaust on these cars is very free-flowing so I'm inclined to think it is just that you can hear the popping more with less muffler to quiet it down.

In any case, the muffler delete is about the most you can get; with the small straight-through can mufflers next.

And no change of muffler these days will make a significant difference in performance, because the factory exhaust flows quite well already.