[Nascort]

Hey all,

I think this is a techy question. What happened to the days of true dual exhaust; when you had seperate pipes going front to back, without the use of and X or H pipe? Why are X/H pipes used now? It seems pointless to me that you would connect both exhaust pathes togather. Thanks for the info!!!


Paul

[Smokey88]

if im correct which is a 50 50 shot i believe its something about the amount of backpressure needed and with a x/h pipe the combination of both pipes helps with the backpressure that way you dont lose too much back pressure and have negative effects on your hp

[stang93mustang]

Originally Posted by Smokey88

if im correct which is a 50 50 shot i believe its something about the amount of backpressure needed and with a x/h pipe the combination of both pipes helps with the backpressure that way you dont lose too much back pressure and have negative effects on your hp

+1, it also helps equilize cylinder pressures

[Gary Paul]

According to Car Craft magazine:

"For any performance exhaust system, some type of crossover connecting the two sides of a dual exhaust system is important because it acts to balance the two banks of the engine. The common H-style crossover is good at balancing sound pulses between the two halves, but does little to promote scavenging because the exhaust gases tend to follow the path of least resistance, which is straight through each pipe rather than taking the 90-degree turn through the H-pipe into the other half of the system. In an X-pipe system, however, where the two sides of the system intersect, the gasses have no choice but to intermingle as they pass through the junction. This promotes improved scavenging effects by smoothing out uneven exhaust pulses from the engine's firing order. It also helps quiet down the exhaust, resulting in a mellower, less raspy tone. According to Magnaflow, the faster acceleration of the gasses through an X-pipe causes them to flow in a linear fashion parallel to the walls of the tubing rather than tumbling. This linear-flowing gas is much quieter than tumbling gas, resulting in an exhaust tone up to 8 decibels quieter than a traditional H-pipe."

The firing sequence of Ford V8s like the 4.6L and 5.4L is 1-3-7-2-6-5-4-8 with cylinders 1 through 4 in the driver's side head and cylinders 5 through 8 in the passenger side head. When the first four cylinders fire in sequence (cylinders 1-3-7-2) three of them are in the driver's side head. An X-pipe is best for equalizing back pressure and promoting scavenging (where the previous exhaust pulse helps pull the next exhaust pulse out of the cylinder and improving exhaust flow from the engine). An H-pipe isn't as good at scavenging, but creates a louder and raspier exhaust tone which some prefer.

[05horse]

those days are still here, thats how im running

[Nascort]

Thanks for the Article Gary Paul! Now I am going to have to lookup scavenging from Wikipedia or something, .

I am not an engineer or anything, but common sense ( ) tells me that back pressure would be bad for an engine . An engine is trying to rid itself of spent gasses, not have opstacles (x-pipe, mufflers) attempt to hold the gasses in the cylenders!? But I can also understand what the article is talking about too.

I'm feeling smiley happy today !

[JohnJon87]

thats y sum ppl hurt their power by buying to big " pipes.. a friend of mine had 3" pipes on a 300 hp GT and it killed his power... you really dont need anything over 2.5" unless running up around 500+ HP

[bmw_ssg]

This is a good read thread here. I just learned something new!

[oldlugs]

I surely wouldn't want "true duals" without a cross-over... Your car would sound like an old motorboat from the 1930s. Neither an X or an H presents any restriction, but only aid in both exhaust extraction, and sound quality. With the cross-over, your car will sound like a V8, rather than a pair of in-line 4s.