MAF Sensor
But the difference was so minimal, so low could have been error in dyno, or change in humidity/temp etc....4-5 horses
If I could start over again with that car, I would have focused on other mods first, namely Headers and Off Road Y, Rear End Ratio, and NOS were the most satisfying mods I made.
My latest car a 2000 Ws6, I just completed the header and ORY...good difference in power and sound!

