As I understand the exhaust backpressure issue (dealt with this a bit when I changed out the exhaust on my previous car... replaced headers and catback, and had a high flow cat installed), some is good for N/A engines.
Some backpressure is good for N/A cars, as it helps with low end torque, but can end up reducing high end horsepower. Reducing backpressure can reduce low end torque, but should help with high end horsepower.
Of course, actual changes in actual cars may differ, so it's pretty subjective.
When you say 'lose power', it's also subjective. 'Power' as in low end torque, or 'power' as in peak horsepower could be different things.
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2001 Boxster - Grey on Grey
1969 911T Targa - 'Stinky'
http://www.zoto.com/frayadjacent/img...f27a-4a399.jpg <---- my car. ^ crap I post.
"The existence of the flamethrower is evidence that someone, somewhere once said 'I want to set those people over there on fire, but I don't want to have to walk over there to do it.'"
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