Originally Posted by
THOR
can u get a true ideas from this type a test. i know some mods u have to tune it for it to come alive and show its true capabilities....
Technically a correctly designed header will simply improve the engines volumetric efficiency by ensuring the blowdown (exhaust) process is as close to %100 complete as possible. The rest of the engine will not have an affect on if it helps or not.
However. Any other restriction throughout the intake filter, throttle body, intake plenum, intake runners, inlet ports, valves (int/exh), back through the exhaust ports and also after the collector, can negatively affect the engines volumetric efficiency. Therefore yes, it makes it hard to see the gains, especially since these headers are not matched to the engines head in most cases and are not tuned for the correct RPM at all. They still make power over stock though because they will flow better with less restriction (all are larger). However too large can be detrimental because you begin to loose the wave tuning affects that are not present in these anyway. Also the increased interior surface area causes greater heat transfer from the exhaust gas which we don't want either.
Walker