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Old 11-20-2006, 10:56 AM
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Crossover Exhaust Discussion

I have several questions that I think a lot of us could benefit from discussing. I have read and heard all kinds of ideas and argument's for/against the crossover. Some racers use them others don't. Can we get the straight story?

1. Is a crossover essential to operating a V-8 motor? Why? Why not?

2. Where is the ideal location to connect the crossover pipe to the header pipes? At the turn heading back? 6" back from the turn heading back? Is there a formula to determine the location?

3. What is the ideal I.D. of the crossover pipe? Same as the header pipe? Larger? Smaller? How much? What is the smallest I.D. one can be and still work?

4. What should crossover pipes stay away from? Oil pan? Tranny pan? Fly wheel cover? Steering rack?

5. Is a crossover pipe that breaks the plane of the scrub line an unsafe location?

6. Does a crossover pipe really improve exhaust sound? Engine performance and horsepower? Torque? Fuel economy?

7. Zero bends in a crossover is probably the ideal. What is the upper limit on the number of bends? Is a 90 degree bend to much?

8> What is the ideal connection of the crossover to the header pipe? Mechanical? Welded?

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Old 11-20-2006, 11:01 AM
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I guess the first thing that needs to be established is:

What is a 'crossover exhaust'?
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Old 11-20-2006, 11:46 AM
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Quote:
Originally Posted by jpd37
1. Is a crossover essential to operating a V-8 motor? Why? Why not?
Certainly not essential, but sometimes beneficial.
Quote:
2. Where is the ideal location to connect the crossover pipe to the header pipes? At the turn heading back? 6" back from the turn heading back? Is there a formula to determine the location?
No formula, and there is no best place that is ideal for all engines. The ideal place to put it is where the exhaust pulses are at a point of resonance, or where the waves "stack up." Manufacturers determine this using pressure sensors every 1/2" back the exhaust. Some home-brew builders determine where to put it by painting the exhaust and seeing where the paint burns off first since the area of highest pressure should create a hot spot. Its also not overly critical since once you tap into the pipe its like pressing a key on a trumpet; you've changed the length of the pipe and therefore that high pressure resonance area might have moved.
Quote:
3. What is the ideal I.D. of the crossover pipe? Same as the header pipe? Larger? Smaller? How much? What is the smallest I.D. one can be and still work?
It depends on the type of crossover. If its an X pipe, it needs to be at least teh same size as the rest of the exhaust. If its an H pipe it can be a little smaller, but anything from 2/3 the diameter up to the same size is acceptable.
Quote:
4. What should crossover pipes stay away from? Oil pan? Tranny pan? Fly wheel cover? Steering rack?
If its an X pipe it will get just as hot as the rest of the exhaust, so I like to cross them just behind the tranny pan to avoid complications. H pipes it depends on how hot it gets, and how hot it gets is often times related to how much the engine needed the crossover. If it gets used a lot (lots of exhaust flow) then it will get hot, but no hotter than the rest.
Quote:
5. Is a crossover pipe that breaks the plane of the scrub line an unsafe location?
You'll have to explain scrub line to me.
Quote:
6. Does a crossover pipe really improve exhaust sound? Engine performance and horsepower? Torque? Fuel economy?
All of the above, yes. But the biggest change you'll probably notice is the sound. It mellows it out and just takes it down a level. X pipes are designed to offer full flow sharing between both pipes. Exhaust pulses choose the pipe with less pressure when they reach the X. For this reason they slightly favor higher RPM hp production. Certainly not enough to change the peak RPM, but a little help. H pipes typically favor low RPM torque production. They don't really flow much exhaust through the crossover, but they remove high pressure areas allowing for more effective scavenging.
Quote:
7. Zero bends in a crossover is probably the ideal. What is the upper limit on the number of bends? Is a 90 degree bend to much?
Well, an X pipe can't really have bends except the one designed into it, but H pipes aren't that picky. Since they aren't actually flowing much gas they can have a bend or two. If you're looking at it from the standpoint of adding power, any pipe is better than no pipe. One with a 90* bend might not do as well as a straight pipe, but only a tiny difference will be noted.
Quote:
8> What is the ideal connection of the crossover to the header pipe? Mechanical? Welded?
I would weld it. You could mechanically attach it like with clamps if you have a Tee in the exhaust tubing, but it gets a lot of vibes. I'd feel better if it were welded.
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Old 11-20-2006, 11:50 AM
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Here are some examples of H and crossover exhausts which connect dual exhausts.
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