There is a perfect part for you. They're called Turbolators (http://www.jcwhitney.com/webapp/wcs/...&storeId=10101
). Come in all kinds of styles as tips or one (part #1004) that is put in in-line (only in 2.25 in. I think). The key idea is that it has a spring loaded flap in the exhaust flow. At cruising speed the flap is mostly shut, which does quiet the exhaust substantially, plus gives the added BENEFIT of MORE backpressure. Result is quiet operation when you cruise plus better low rpm torque and as a direct result better mileage too. When you stomp on the gas the higher exhaust flow rates push the flap wide open, nearly eliminating the restriction at the full throttle operation. So you can 'have your cake and eat it too'.
Ferrari uses a variation of this active exhaust idea in their cars. Active mufflers based on this idea are under development and will be seen in a lot of new cars in the near future. A much more expensive part called a T-Rex was available until recently that did the same thing for radical offshore boats. These boats benefited from the the tips, it gives them better 'out of the hole' acceleration, but does not hurt top speed. If you think about it everyone on this board could benefit from such a self-tuning, load sensitive exhaust system. No more trade-off between high load performance and low load performance.
I've just ordered the inline version for my car. My 283 suffered in low end torque and mileage when I switched from stock exhaust to headers and dual. Sounded cool but otherwise it was not such a good idea as I got significantly worse mileage, and I couldn't spin the tires off the line anymore. And gas mileage in Germany at $5 bucks a gallon is a major concern of mine. Once I install them I'll report back how they work. Incidentally, the in-line version is not produced any more. There are about 100 pieces available at the Canadian distributor (as of March 2004)www.ultrafitexhaust.com
.They can be ordered through Speedy Muffler in Canada.
I'll probably be laughed at by a lot of guys now. Almost everyone believes the 'less-restriction-in-the-exhaust-the-better' myth.