I have seen a few videos, most notably one from EngineMasters, that compared H-Pipe to X-Pipe exhaust configurations. What I took away is either is better than neither, although the HP gains folks might be expecting will disappoint. I also ascertained an X-Pipe configuration apparently does a better job at muffling the more shrill aspects of an exhaust system sound, which is what I was wanting to rectify with our 73 Mach 1's exhaust. In our case the engine is a 1994 351W (not C) built for street/strip performance. It had Hooker long tube ceramic coated headers, and had FlowMaster 40 mufflers. I liked the sound overall, but after 20 minutes of driving I was ready to take a break due to the droning, especially at highway speeds. I initially replaced the FlowMaster 40s with a muffler with a bit more sound dampening. I noticed three things:
- the exhaust sound was muffled a little more, but not by a lot
- the droning persisted
- the engine running temperature increased by 2-3 degrees as the hot exhaust gas was not able to be sent out easily as compared to the FlowMaster mufflers
So, rather than corked up the exhaust with even more restrictive mufflers, I decided to have an X-Pipe fitted, where as the headers fed their own exhaust pipe t no crossover/balance tube between the left and right exhaust piping. In an effort to really help dampen the exhaust sound that was causing the droning I had the X-Pipe designed with a more than expected/optimal (for performance) series of bends. The idea was to give the sound waves "something" to crashed into a few times as the hot exhaust gas was making its way out of the piping. This would no doubt prevent me from maximizing any even marginal gains in performance. But, I also felt it would still be better than no X-Pipe or H-Pipe at all.
Attached are some photos of the X-Pipe that was fabricated, and showing it installed.
The result of my 2nd run at resolving the exhaust droning include:
- No more droning
- we have a deeper sounding exhaust system
- the engine running temperature dropped by 2-3 degrees, apparently because it is once again easier for the hot exhaust gas to escape despite having replaced the FlowMaster 40 mufflers previously
So, it took me two stabs at the problem getting resolved. I wish I had done the X-Pipe before removing the FlowMaster mufflers, but at this point I am fine with how things are running (and sound), so I am leaving well enough alone. Here is a link to the one EngineMasters video I had watched a few months before I made my decision re: H-Pipe vs X-Pipe.
https://www.dailymotion.com/video/x5s8nr8
They get into the H-Pipe vs X-Pipe discussion at about 10:00 mm:ss into the video, although I felt the entire video was worth watching, more than once over the months before I made my move.
No regrets.