I replaced that with my early Hedmanns (which are not very good headers in todays world) and a pair of 30"x 2 1/2" collecters. The car ran exactly the same speed and ET either way. Makes me think the X pipe system makes more HP than the headers since it's pulling more weight to the same speed. I have not pursued this any further, since I run "Pure Stock" and the 2 1/2" system is legal, there's no reason to experiment further. 

Due to the imbalance of the firing orders from bank to bank on a V8, a crossover pipe will enhance lowend torque.  The closer the pipe is placed to the engine, the better.  X pipes are the ultimate in crossover pipe technology as the distance between the two exhaust pipes or tailpipes becomes minimal.  The Mustang mags have tested this to death and although I don’t recall the numbers, the crossover pipes always helps where the system must be run with a full set of pipes.

And here’s why the crossover pipes work.  When examining the firing orders of any V8 with a 90° crankshaft, you’ll find where two cylinders on each bank fire consecutively and then miss a beat.  The crossover pipe helps to balance out the surge in exhaust pressure in a tailpipe that is a result of cylinders on the same bank firing back to back.  That pressure surge ends up in the other pipe and eventually into the other muffler.

Ford and Mercurys started using crossover pipes in the early Sixties on the dual exhaust equipped cars if that’s any consolation.  For the race cars, 180° headers are available for some applications where clearance permits them and this allows the firing order to alternate between paired collectors in a defined manner.

Here’s another thread with some similar information.

http://www.y-blocksforever.com/forums/Topic44336-3-1.aspx

    To add to what Ted said here, and this is only an opinion, I think the fact that each cylinder exhausts into two mufflers instead of one, helps lower the maximum pressure spikes. This effectively lowers the backpressure each cylinder sees. I've read the same articles in different Hot rod magazines, in all cases there was a noticeable difference in low end to midrange torque. Top end, not so much. I suspect the advantage is exagerated in my case because the motor makes comparitively less torque until the blower spools up. i need everything I can get at launch. 

I ran the same thing for several years on my dirt track sportsman and was convinced they helped pull the car off the corners on the smaller tracks with tight corners.You're sure right about them being a pain to install.Maybe the best thing about them was the unique exhaust sound.Everyone could always tell where I was on the track because of the sound.My son always said it sounded like a pissed-off hornet.

   Charlie, not to any serious degree. Jets (secondaries) are impossible to find for Teapots,the primaries were not affected. I tried timing, but it made no noticeable difference. Most of my mixture issues have been just keeping enough fuel in the float bowls. When I have that solved I'll play with jets. For now, with the blower, I prefer rich enough to keep the pistons solids rather than liquid! 

  Glen, I think that the "finding room in the car" issue is probably what killed the 180's. They don't seem to work enough better to warrant the added weight and hassles. Except in Formula 1, and I could care less about those clowns.