How can an X pipe be good?

I understand having connection between pipes can help balance the exhaust pressure and help scavenge like older H-pipes. But when you take two 2.5" steams of hot, flowing exhaust gas and cross them, making them occupy the same space for a small time, it seems like a restriction to me. It's like two 2.5" pipes into one 2.5" pipe then back into two.
If the motor is idling, you might imagine alternating putts, just missing each other, but at 2K RPM & up, it is like 2 solid streams colliding with each other?
Anybody follow me on this?

Back pressure. Straight pipes sound like junk and I lose power

Thank for the detailed explanation!
I never said anything about straight pipes. I understand how the right muffler(s) and proper size pipes keep proper velocity up, but I don't understand how an X does anything but harm.

Put one on and see. I'm sure if they harmed your vehicle people wouldn't have them on.

And don't buy one. Any real exhaust shop can make one for about $15. They can also make the spot where you say the air sits a little longer. I had mine made just for that reason. Ones you show look too small

Not sure if you can see it above the exhaust brace but X Pipes are stock on the Charger



From my understanding many manufacturers as well as gear heads switched to x pipes because they were not as loud as an H pipe, provided better fuel efficiency and works well with today's emissions equipment. I can't see how it would be a bad thing. lol

I know they are out there and are viewed as a good thing, I just don't understand why. It seems like making 2 flows of exhaust gas occupy the same space at the same time would be a restriction?

i robbed this from another site on the web,,its collectively all the post on that particular thread summed into one

X-pipes have consistently shown an additional 10 HP or so more than true dual exh. It allows more efficient scavenging and reduces retrograde pressure waves from causing exh. gas reversion. They also drop the sound level a notch, also. An H pipe does the same thing, but not as efficiently and is more difficult to properly place. from a z28 website

^^^ What he said.

Running an x pipe on my mustang, def love it ... can feel a little power increase over the stock H pipe ...it is quieter BUT of you are running straight pipes than it helps with back pressure as well as sound

The setup i have on my stang:

Originally Posted by mikeb33

I know they are out there and are viewed as a good thing, I just don't understand why. It seems like making 2 flows of exhaust gas occupy the same space at the same time would be a restriction?

The exhaust pulses from the left bank are not likely to reach the x at the exact same time as those from the right bank, as a result a vacuum is created with the leading pulse pulling the trailing pulse...aka scavenging

Google exhaust scavenging for a more detailed explanation.

I know they are out there and are viewed as a good thing, I just don't understand why. It seems like making 2 flows of exhaust gas occupy the same space at the same time would be a restriction?

The real answer is that the gas from two cylinders does not occupy the same space at the same time. The gas comes in pulses, not a continuous flow. This happens very quickly of course, but it does happen. If it did not, then exhaust tuning (headers, etc,) would not work. But they do work.


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is there a performance benefit replacing y pipe single in, double out setup with a dual w/x-pipe setup?

2nd question: performance difference between duals w/x-pipe dual mufflers vs. dual in dual out 1 muffler with internal x-pipe?

Kind of long but came across this write up:

How And Why "X"-Pipes Work
By Bruce Wayne, MagnaFlow Performance
There has been an enormous amount of press about getting more out of performance exhaust systems. By incorporating "cross-over" or "X"- pipes in dual pipe systems, to balance out flow, many enthusiasts have found an extra edge. However, the perception is that this is new technology. Nothing could be further from the truth. But, why is an "X" pipe better than an "H"?

The reason an X-Pipe crossover works better than an H-pipe crossover isn't more flow because of volume, but more effective use of exhaust gas velocity. Exhaust gas (or air) has surface tension, and flows much like liquid would through the same pipe system. As the cylinders of each bank on a "V" style motor fire, they create a pulse in the system. The pulses will alternate back and forth from bank to bank as the motor runs. With multiple cylinders, such as a V-8, the eight cylinders alternately fire creates lots of pulses in the system.

If you put your hand behind the tailpipe, it would feel like a constant flow of air, but what it really is a lot of singular pulses giving the impression of constant flow. The idea behind the H and X style crossover is to unite the two banks of cylinders for better exhaust gas scavenging. Instead of two separate banks of four cylinders doing their own work, the crossover uses the pulse created by a firing cylinder of one bank to create a vacuum in the other bank because of surface tension. When a cylinder of the other bank is ready to fire, instead of the piston having to force the exhaust gas out of the cylinder, the vacuum that was created by the other cylinder bank helps suck the exhaust gas out of the cylinder, hence the term "scavenging."

Whenever you can reduce the load on an internal combustion engine, you are likely going to see performance and efficiency benefits. The difference between an H and X crossover is a smoother path for the exhaust gas to follow. Exhaust gas, like a liquid, will follow a path with the least amount of resistance. An H crossover has a path with two sharp 90-degree angles that are close together. An X crossover has a path with a much more gradual bend to allow the exhaust gases to continue their path back out to the ends of the tailpipes, rather then turning sideways for a short distance, then turn again to head out the tailpipes. Smooth flow with high velocity means more power by use of scavenging. Using an exhaust system with too large of piping diameter work against scavenging in the same way that running an exhaust with too small of tubing chokes the motor and forces it to work harder to expel the exhaust gases.

Thank you for that good explanation. Do you think it matters where the X pipe is in the system? On oem exhaust they are usually close to the front. I was thinking of using a Magnaflow "True X Muffler" in the stock location, but that is further back than our Y pipe or the normal X pipe location.

Will the internal X work properly if the both pipes going into it are different lengths? (left side crossing under the trans and and meeting the right side with the DI/DO in the stock location)

Im wanting to utilze the stock 2.5" size but adding a magnaflow x pipe where the stock y is. And going 2.5" all the way back. Will this be performance beneficial on a 10 ram hemi w/ sc flashpaq, s&b intake, and a hand ported throttle body. Or will it be a waste of time.

Btw as of now i have a flowmaster 2.5" in. And 3" out scavenger y pipe. Utilizing the factory duals.

Intake= more air in. So yes it would help.

I see you went with 3" w/ a x-pipe did it help you or hurt.

I think it helped. With cai I got 19.4. After new heavier wheels I'm at 18.3 on plus gas without a tuner. I plan on headers when tuner comes out.