What is the purpose of connectin the two pipes with an H or a Y?? I obvioulsy know it is to equalise the pressure between the two pipes but i want to know why it is required? Why would it not be OK to just run two independant pipes, one from each bank of cylinders with no connection between them?

Cheers,
Richard.

i'm not positive but it mabey for back presure

Running individual pipes with no equalization is fine.

So why do so many exhausts have it?

Because it performs slightly better with equalization than without.

It's like single vs. dual. Either one "works", one is just a slight improvement on the other.

The actual name for the "H pipe" is called a RESONATOR PIPE. As exhaust goes through the pipe it resonates. On dual exhaust, you have a left bank resonation and a right bank resonation. The way the cyliders fire, 1,8,4,3,6,5,7,2. On Fords, 1,5,4,2,6,3,7,8 (if you look close the cylinders on both Ford and GM fire exactly the same, but, since they are numbered differently, that's why the different firing order). So if you notice, 8 and 4 are on the same (4 and 2 for Ford) side and 5 and 7 (7 and 8 for Ford) are on the same side. So you get 2 cylinders firing on the same side one after the other. Left, right, right, left, right, left, left, right. With the 2 cylinders on each side firing back to back it creates an off resonation. With the "H pipe" it helps to even the resonation for both sides. That's the reason for it, nothing else.

Thanks, that makes some sense.. now what is the adverse affect of the resonation? why is it undesirable? Vibrations or noise maybe?

The reason that i am so interested is i used to drive a Subaru Impreza and the noise it made was simply awesome.. the headers were unequal lengths and so you heard the two banks of cylinders (boxer 4) firing at different times giving it a kind of beat...

Also the old TVR V8's (www.tvr.co.uk - you dont get em over here) and they sounded even better.. of course they ruined it lately by using inline 6 cylinders but i heard one of their V8's one time and you could almost here each individual cylinder firing - that is how i want my camaro to sound if i ever manage to get that far into the project i am planning :-)

So basically i am wondering if running 2 individual pipes without a resonator pipe will give me that noise i am looking for?

Cheers,
Richard.

Remember, the muffler does exactly what it says, muffles the sound. It does not create back pressure. If it does, it's bad and needs to be replaced. The vibration of the baffles in the muffler is what gives it the distinctive sound. That's how muffler manufacturers change sounds between different mufflers. That's why when "people" say that a cat back system increases HP, I have a hard time with that. The most restrictive part of the exhaust system is the CAT. After that, there should be no restiction. Another factor to exhaust sound is the pipe. Factory pipes are double wall. Aftermarket pipes are usually single wall. The double wall will keep it quieter, which is why "they" use it.

You could always go without the H pipe, and if you don't like the resonation, add the H later. The resonation just wouldn't be as even as with the H. You may or may not notice it.