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Message: <blockquote data-quote="AaRoN" data-source="post: 851932" data-attributes="member: 8691">Sure thing:First of all when it comes to modifying a car, bigger is not always better. In this case, it holds true to my point. Larger diameter exhaust piping does increase flow but decreases velocity. Velocity equals torque and flow equals horsepower (when speaking of induction and exhaust). Too large of an exhaust also reduces the scavenging effect. The general rule for a car with a 250-300 cu. in. engine making around 300HP (n/a) with dual exhaust should have a 2.5" exhaust for optimum performance and scavenging. When the piping is too big it also has more heat transfer. Meaning the exhaust gases are cooler, thus moving slower. This is the purpose of header wraps. The thermal barrier on the headers reduces the amount of escaping heat which speeds up the exhaust gases inside the header. Scavenging is important to help remove all exhaust gases from each cylinder. Without that, what's the point of the exhaust system?</blockquote>