On my SD I've made a couple of sequential changes to the exhaust which have improved throttle response and overall performance. First, I had the kidney-shaped resonators cut out and replaced with straight pipe. In addition to removing some weight from the car, the engine really woke up, even on a car with 300+k miles on it. The exhaust note was only very slightly louder but the engine was far more responsive. However, even though the car ran better I wasn't wild about the *sound* of the exhaust, so I had the rear muffler replaced with a straight-through Magnaflow muffler in the stock location with a simple turn down tip. I bought an aluminized muffler, not the stainless Magnaflow product, so the cost was quite modest. Since I have a 110 mile daily round trip commute I was not interested in anything loud, and I guarantee this setup is no louder than stock. However, the car runs so much better than with the stock system that I am now thinking about backing off of my ALDA adjustment and seeing if I can pick up some additional economy. As it is, the changes I made helped me gain a couple of mpg. One nice side benefit is that when pulling hard, such as up a long hill under sustained boost, the engine peak temperatures aren't quite as high (10-15 degrees cooler according to the guage) and on the downhill portion the engine cools off faster. In normal driving situations the thermostat controls engine temp and there is no change. Food for thought for those thinking about modifying their exhaust systems as a way to improve performance. And no, I did not do any GPS verified pre- and post-mod 0-60 or other tests--it's a 20 year old car with 325k miles; I'm not going to beat it, but rather just want to optimize its performance as the miles roll on.

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Richard Detoy
'84 300SD
'76 Moto Guzzi 850 Le Mans