I've never been a fan of pipe wraps, except for turbocharged race cars. Wrapping keeps the heat in the pipe, which is what you need to keep your turbo spinning. But, keeping that heat will tend to deteriorate your pipes, especially if you live in damp country, and....be harder on your exhaust valves. It's this latter problem that puts me off.
If one gets a performance advantage from ex. pipe wrapping, it would seem to me that his engine is over exhausted, and the extra heat increases the exhaust volume. The extra gas volume has a harder time getting through the same sized pipes and mufflers, creating more back pressure. Increasing back pressure to get better perf. says that your overall system is in need of attention, as it is lacking somewhere other than the ex. system.
