Dear AquaTune, I have an '89 GMC 2500 converted van with a 350 V-8 engine. Before I installed your unit on this particular van, I was getting 16 mpg at the very best and having predetonation problems, which is why I was using premium fuel! I immediately jumped to over 20 mpg with low-octane fuel. Also, the increase in hp is fantastic. I am very pleased with your product.