I thought the same thing. WHAT! Someone crushed my downpipe?

They're all like that. And yes they do restrict flow. We put a Downey aluminized header(the cheaper one) and downpipe on my 98 XJ and it really opened it up. I had the auto so it's hard to tell exactly where the power band is. It stopped downshifting on every single tiny incline though. It would stay on gear much longer and felt more powerful.

K&N drop in air filter was next. No noticable diffence but sounded a bit deeper. High flow cat and larger dia exhaust pipes and muffler were last. Helped bring up my MPG a bit but it was still around 17MPG.250miles from 15 gallons instead of 220 miles. Better than the 12 or so I was getting from each fill up but the $600 I spent on the header and exhaust would buy a lot of gas.

Sounded great and quit downnshifting every time I hit a hill but as for actual HP or MPG it would have to be dyno'd.