Auto Parts: Performance parts, poor gas mileage, horse power

Question
Hi,
Do those things that you add to the vehicle's engine to increase performance really work? See link below. Thank you.
http://snipurl.com/16tqx

Answer
it might work. but i wouldn't waste your time. what it doesn't say is that by enriching the fuel all of the time you will get poor gas mileage, tend to foul your plugs faster. and will carbon up everything( catyltic convertor). plus i would say at most you might get 3-4 horse power.