Air filter

[TeamGreen]

I just put that extesion that goes from the airfilter box to the side of the fender where the intake comes in. My 89 sierra didn't have this when I bought it. What exactly does this do?

[76BBSub]

If you're talking about what I think you're talking about it's a duct to direct cool air from in front of the truck (throught the fender and grill) into the air intake.  This does a couple of things.  Primarily, it is designed to provide the engine with cooler air, which is denser and so makes a little more power.  It also directs the noise of intake air being sucked into the engine away from the passenger compartment.  You are probably better off from a performance and engine temp standpoint with the duct in place, as you now have it.

Jeff