A stock system is designed to reduce and if possible eliminate all the noise produced by your vehicle. Because of this, the axle-back exhaust system does not impact the flow or pressure of the exhaust gases in any way. The axle-back exhaust system uses the factory exhaust pipe which does not have a large diameter. This offers even more breathing space for the engine thus better performance. Most cat-back exhaust systems are customized and not universal. One is to replace specific parts like with cat-back exhaust systems.
The difference is that the dual exhaust system has two exhaust systems on one vehicle. Meaning, when modifying your exhaust, never start from the front of your turbocharged vehicle with a downpipe or with headers on your naturally-aspirated platform, you will create a bottleneck in the flow. By starting with a cat-back first, your exhaust gases will flow more freely if the rest of your system is stock.
From the inception of the small block Cobra, Carroll Shelby intended to build a race version of his lightweight roadster