I've seen a few of these products that you put into your engine once, like you would oil, and it increases both your horsepower, and fuel efficency. I was wondering if anyone else has seen, or tried this, and whether it actually works, and what kind of gains they recieved, thanks.

 

None of these products work. Sorry to be repetative, but the FTC has sued just about every Slick 50 type additive maker and they either paid huge sums of money or closed up shop. There are no miracle fluids!

 

Plus you could be "poisoning" your catalytic converter in the process.