Equal vs Unequal length headers
 

I have done a search on the forum but not sure I really have a good answer to this one. Equal vs unequal length headers on a turbo motor (specifically a 930). As I understand it on a normally aspirated engine headers do two things. First they reduce exhaust back pressure by essentially giving each cylinder its own exhaust pipe. If all the pipes are the same length to the merge point (collector) then each exhaust impulse reaches the collector at a different time and they do not interfere with each other which also helps reduce back pressure. And the second thing headers do is allow "tuning" of the exhaust to a certain "frequency" (RPM) which creates better exhaust scavenging at the selected RPM. This allows for modification of the engine's power band. So the question is how much of this applies to a turbo engine where I would imagine the most significant part of the exhaust backpressure is from the restriction of the turbo charger. In this case the most significant improvement from headers on a 930 is shortning the distance to the turbo allowing for quicker turbo response. Thoughts?

I went through an exhaustive (pun intended) study when designing my headers. Turns out I was re-inventing the wheel as a few other tuners had already produced a very similar design.
Without any doubt tuned headers have an advantage.

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/461519-latest-project-headers.html?highlight=Headers

I've been told by Porsche turbo tuners equal length headers for big HP / track usage, and shorty headers for quicker spool street usage.

How "fast" the turbo spools is partially dependent upon tube length. If the tubes are really long, such as SSI, you may notice a difference. That slight difference disappears with medium length primaries. The torque gains off boost also make any lag less of an on/off switch.