These spacers do not provide any gains in HP at all.  They claim to increase TQ and MPG but we tested one and it gained nothing.  The Dyno showed no gains in HP or TQ.  We also had contacted one of the manufacturers for their comments on them and here's the direct quote (from email):

--------------------------------------------

From: AirAid Info
Subject: Re: AIRAID.COM Contact

Dear Sir, thank you for your inquiry in our products. The spacer makes no HP on the Dyno. It makes all of it's power in torque in the low end. If you haven't noticed any power on the Dyno or the track then it's doing what it's supposed to. You would not see any gains down the 1/4 mile or increases on the Dyno. The idea of the spacer is to improve overall drivability and fuel mileage. In most cases when people install a bolt on part they expect better mileage and power, what happens is they are into the throttle a lot more than before trying to test performance and that's when the decrease in mileage happens.

Sincerely,

<Airaid Technician>
-------------------------------------------

Points to look at:

• "The spacer makes no HP on the Dyno. It makes all of it's power in torque in the low end."
  
• "If you haven't noticed any power on the Dyno or the track then it's doing what it's supposed to."
  
• "The idea of the spacer is to improve overall drivability and fuel mileage."

So...it doesn't make any more HP, is not supposed to help in 1/4 mile performance (or on the Dyno), and is mainly for mileage and bottom end Torque. Well, Dyno's show TQ figures and there were no changes, mileage stayed the same, and 1/4 mile performance wasn't affected on the several others who have tried it