Originally Posted by 370ZFan

I have a completely different theory on why the numbers are so strange.

Relentless,
Please don't take this as a personal attack, but you may want to get another dyno done because these are highly unlikely to be accurate.

Horsepower is (tq x revs)/5252. As such to make more horsepower, one must either a. make more torque at the same revs b. make same torque at higher revs or c. both.

The red line going straight down on your dyno plot is showing at what revs you are making the numbers listed at the chart.

Comparing dyno 1 to dyno 2:
Dyno 1, you are making 283.1 hp and 209.8 ft/lbs at around 7100 rpms - with the pull going up to around 7350 rpms (short of redline).

Dyno 2, you are making 288.6 hp but somehow making less torque at 195.2 so the only way for this to be possible would be to make it at higher revs, which you do according to the chart. Only problem is that it says that was revving 7775 rpms - past redline and that the pull went to almost 8000 rpms before letting up - which is past fuel cut.

My opinion: a faulty reading on what revs you were at threw off the reading. Truth be told, STRICTLY JUDGING FROM THE PLOT ALONE, it appears that you lost a significant amount of power throughout the curve - which would be shown if you put one on top of the other and shifted the plot left by 500 rpms to compensate for the clearly faulty RPM readings.

HOWEVER, I'll reserve judgment on whether you really lost power for your next dyno simply because there could have been other factors/errors which could have come into play, esp. if I am right on my faulty RPM read theory.

So in conclusion, I believe that well...these dynos are anything but conclusive on the topic of power gains from Stillen Headers.