I don't know if they solved the issues with these since I haven't looked into them in years, but here's the issues they used to have and why it was a BAD idea to buy one.
1. It's adding something in the flow of air which restricts air flow at idle and partial throttle. The old kits were set up to only activate under heavy throttle so it hindered performance at all times unless you were heavy on the gas pedal.
2. The motor and/or blades of the fan were not able to flow enough CFM at higher RPM's. Sure you'd get a little bit of boost at low and mid RPM range, but at higher RPM it just could not keep up with the air flow so like the issue explained in #1, it actually hindered performance at higher RPM's.
3. The fan blades were not made out of good material and there were reports of the blades breaking off and getting ingested by the engine causing SERIOUS damage. bent valves, dented valve seats, dented pistons, scratched cyl. walls, and destroyed rings are a few damages that come to mind. It should be a concern of yours to say the least.
4. The motor would burn out after only a few months on the car. I don't know if it was just bad design or if the motors are just not capable of spinning to a fast enough RPM and burn out trying, but they don't last very long.
In THEORY, these things are GREAT power adders and a big bang for the buck. In ACTUALITY, they don't really help with performance that much and end up being a waste of money. If the design was improved upon and had proven results then I would be all over these, but the #'s just aren't there.....at least not yet.
And just to let you know, a friend of mine actually bought one of these kits about 6 months ago despite me trying to talk him out of it. He installed it, said he liked the sound, but didn't really see any major power gains and scrapped it and put a REAL turbo on his car. Now he giggles like a little school girl everytime he hits the throttle
In fact, everyone I know that has tried this ended up pulling it off their car shortly after installing it. Take that for what it's worth.
