Somethings wrong.  Eighter there's soemthing wrong with your car, or the muffler shop is feeing you a line, possibly to get you to buy a second set of cats?

I've run several cars w/ and without the anti-smog air injecton system with out problems.  Some legal, some not.  No mustangs though.

In the pre-emissions era, none of the cars had the air injection system.  The air injection system that is included with the cats is there to reduce emissions.  Even with the best fuel control system, there is some NO, CO, and VHCs (Volital HydroCarbons, partly burnt gasoline. ) are created.  In the triple element cat, the first just deals with the NO.  The first element basicly needs to have a little O2 in the air as possible.  The second element is a mix that deals with the CO, and for that element to work right, you need a as large an amount of O2 in the stream as possible.  The solution is to use the smog pump to inject the air after the first element.  It's not used to prevent backfires.

You see, backfires only occur when you've got too much fuel in the exaust, basicly, your mixture is way rich.  If your fuel system, be it a carb, or injection, is controling the mixture right, nearly all of the fuel will be burnt in the engine, not in the exaust system.  If you've got backfires, you need to deal with igntion or fuel problems, not exaust.

The problem with running w/o a smog injection system, at least in Texas, is that every car made after like 65 has to have one to be inspected.  Before 84, you don't have to have a cat, but you have to have a smog pump, EGR valve, O2 sensor, etc...  The way to have it riged up without cats legaly, is to have a set of holes cut into each exaust mannafolds, or headers, and have the air injection plumbing plumbed to there.  Each states emission laws are a bit diffrent, so I'd check with your local inspection agency, and see what you need to have to be legal.  California is of course werid.

H pipes or X pipes are suppost to be better for power because of exaust harmonics.  When you've got a dual exaust system, you've actualy got 2, slightly odd fireing, 4 cylinder engines.  The result is that the cylinder's pulses don't line up right, and you don't get as much power.  Solution, install a H-pipe or X-pipe, and now instead of haveing 2, 4 cylinder engines, you've got a single 8 cylinder engine, and it's suppost to make the pulses in the exaust system more even.  Hopefuly resulting in a better sound, and more power.  I'm not sold to the concept just yet.  I know some guys that swear by it, but I can't vouch for it.

Thats the problem.

I have no dyno sheet confirming that an H pipe, or X is better.  As of yet, I havn't installed one, and made a dyno run.  I heard of several that have, but ain't no way I'm checking out a couple of 100 dyno sheets that it would take to staisfy me.

X is better, H is cheaper, usualy, but not by much.  Get what you think you can afford/need.

Eighter way, he shouldn't have to worry about backfires, w/ or w/o the X-over, or H-pipes.  That sounds like the exaust shop makeing something up.

I don't have hot roder, magazine, how many Olds, and how many diffrent sets of pipes?

Exauste tuneing can be very complicated bussness.

What works for one car, doesn't work for others.  I'm not convinced that the X cross over is ALWAYS better than the H pipes.  diffrent mufflers, diffrent levels of back pressure, diffrent shockwaves movein thourgh the system, diffrent mounting points, etc...

But I'm not going to argue with you that H pipes are just as good.  I'm saying I don't know, agreed?

But eighter way, straight, X, or H, there shouldn't be a backfire in sight.

I didnt think that taking the smog sensor thingies would cause backfiring.  I am about to have them taken out any way.  The flows that I put on made the car quiet and I dont like it.  Maybe removing the cats will make it a little louder for the time being until I get my X's.  They are the quietest set of flows I have ever heard.  They are 2 chamber 40 series flows and they dont sound nearly as good as the ones on my buddy's 87 gt t-top.  I am thinking of just taking the flows off and having straigt pipes.  As for emissions, Alabama has no laws or inspections on it, and from what Ive heard there is no intent to start inspections any time soon.  Im not really worried about getting a ticket for a loud exhaust either (fringe benefits of my profession i guess):)

What would you fellas reccommend for that loud throaty sound? complete exhaust.  one of the first things im doing to the car.  Only mods currently are huge taylor racing wires (10mm i think)  and a k&N 9 inch cone filter which is being replaced tommorrow with a march ram air.

If you want a deep throaty sound, gut out the back of your flows.  No turndowns. No tailpipes. If you can lose your cats that will just add to the sound.  Try it and I think you'll be impressed

To answer your question, yes most manufacturers provide for the air tube, and in my case, BBK gave me a rubber extension to make everything fit right when I cut the old one out.  Just make sure when you order whatever you order, you note that they provide for the stock collector tube, and you'll be fine.