i heard it was 11 hp to the wheels...or was it 11 at the crank?
idk, but they are awesome from what I have heard
i've heard 11 at the wheels--but different dynonameter models measure whp differently so 2 horsepower can likely be attributed to model differences.
that said..the trial header is still the top-performing header for the gts engine--but for a price.
awesome addition to your car bro, you'll enjoy it tremendously