Purpose of Crossover
Drifting
Joined: Mar 2005
Posts: 1,806
Likes: 3
From: Burlington WI
I found this article...
http://www.vetteweb.com/tech/0307vet_xpipe/
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.
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.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
That's a great explantion. Somebody's dad had a sense of humour I wonder if the author disappears from work for periods of time when a seroius crime is commited 
Team Owner
Joined: Jun 2004
Posts: 20,216
Likes: 4
From: Smile, it's just the internet.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Are you asking about the exhaust crossover through the intake manifold or the X-pipe?
If it's about the crossover in the intake then that's something very different. It heats the intake's plenum floor so that the fuel will stay in a vapor state. It's also for fast manifold heat up when the engine is cold so get the gas cooking. A cold manifold tends to puddle fuel. And in many chokes, the crossover gives the choke direct heat so that your carb will come off the choke faster.
If it's about the crossover in the intake then that's something very different. It heats the intake's plenum floor so that the fuel will stay in a vapor state. It's also for fast manifold heat up when the engine is cold so get the gas cooking. A cold manifold tends to puddle fuel. And in many chokes, the crossover gives the choke direct heat so that your carb will come off the choke faster.
Race Director
Joined: Aug 2004
Posts: 10,628
Likes: 132
From: Duvall, WA
Originally Posted by gerry72
Are you asking about the exhaust crossover through the intake manifold or the X-pipe?
If it's about the crossover in the intake then that's something very different. It heats the intake's plenum floor so that the fuel will stay in a vapor state. It's also for fast manifold heat up when the engine is cold so get the gas cooking. A cold manifold tends to puddle fuel. And in many chokes, the crossover gives the choke direct heat so that your carb will come off the choke faster.
If it's about the crossover in the intake then that's something very different. It heats the intake's plenum floor so that the fuel will stay in a vapor state. It's also for fast manifold heat up when the engine is cold so get the gas cooking. A cold manifold tends to puddle fuel. And in many chokes, the crossover gives the choke direct heat so that your carb will come off the choke faster.
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Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by Brettmc
I didn't see anything on how to figure out where to put the X. School me up.....
Brett
Brett
The optimum position I was taught years ago was 18 inches behind the header collectors. Unfortunately on a C3 that's not possible.
Drifting
Joined: Mar 2005
Posts: 1,806
Likes: 3
From: Burlington WI
There are some good ideas here...
Originally Posted by Brettmc
I didn't see anything on how to figure out where to put the X. School me up.....
Brett
Brett
There are quite a few pictures on this site but no Vette installations.
I have been seeing them installed after the cats and of course with no cats at all.
Chris B