The Stillen Spark Plug amp is actually made by HKS, and i should change my sig to say that too. I think the address is http://www.HKSUSA.com. It makes the spark plugs ignite at a higher temperature and from what ive noticed compared to when i didnt have it installed, it gives you a slight increase in gas mileage and also has been rumored to givea few points of HP due to better efficency, but i havent Dyno'd it yet, so dont hold me to that.