Stepped vs Standard Headers for FI

[pokeybritches]

Curious as to what everyone's thoughts are as to whether stepped headers are better for FI. A quick Google search didn't net much intelligent discussion.

In a naturally aspirated engine, stepped headers are known to have superior top end while standard headers produce better gains in the low end. However, forced induction makes significant changes to the torque curve, and I know of no FI-specific header designs. There are at least three factors at play - rpm (exhaust pulses per minute), heat (greater at high rpm), and torque (the size of the boom).

Stepped headers improve scavenging at high rpm (when torque is actually lower because the engine isn't operating as efficiently) through the use of smaller diameter piping, which increases velocity.

In the lower rpm, torque is higher and exhaust pulse rates are lower. Standard headers have better performance in this range, which leads me to believe that when torque is high, standard headers are better.

FI increases torque, not rpm, so wouldn't you want the headers that produce the largest gains when torque is high? My hypothesis is that for a FI application, large diameter stepped headers (which no company I know of produces at this time) would produce the greatest peak power. In their absence, standard headers may actually be better due to the increase in high rpm torque (the amount of air the engine is trying to push out could be choked by the smaller diameter piping in the stepped headers, which were optimized for NA applications). Thoughts?

[Beedub]

Euro headers are all you ever need imo, my car felt a big bump in Tq with the large bore section 1, hopefully my butt dyno isn't failing me!