Here's a breakdown of why:
* Factory Design Considerations: The smaller single pipe at the end is likely a cost-saving measure. It's also possible that GM engineers tuned the exhaust system to balance performance with noise and emissions regulations. A larger diameter all the way might be louder and less compliant with those regulations.
* Potential Bottleneck: Going from dual 2.5" to a single 2.25" creates a restriction. This *could* restrict exhaust flow, particularly at higher RPMs where the engine produces more exhaust gases. This restriction *might* lead to a slight loss of performance and potentially slightly higher exhaust gas temperatures (though usually not enough to cause major damage).
* The "All the Way" Approach: Running dual 2.5" pipes all the way to the end (or even merging them into a single larger diameter pipe, like a 3") *could* improve exhaust flow and potentially offer a small horsepower gain and perhaps a slightly better sound. However, this isn't guaranteed. The gains might be small and possibly offset by increased noise.
Conclusion:
Whether switching is worthwhile depends on your priorities. If you're aiming for maximum performance gains, upgrading to a larger diameter exhaust system (possibly dual 2.5" or a single larger diameter) might be worth exploring. However, the gains might be minimal and not justify the cost. If you're happy with the current performance and sound, there's no urgent need to change it. The existing setup is not inherently flawed; it's simply a compromise between cost, performance, and emissions regulations.
