Just wondering something here. I noticed that after I installed the Magnaflow Cat that I am getting a hell of a lot better gas milleage. I used to barely make it 2 weeks without having to re-fuel and now I am going on a 2 and a half weeks and still my tank sits at 1/4. I haven't installed my new o2 sensor yet but I plan on getting that done. I waswondering if a cat can somehow increase gas milleage?

 

Certainly. A restrictive and/or plugged up cat will hurt power and efficiency.

 

but yet wouldn't a more flowing cat (free flow) make it so the engine runs better thus causeing you to use more gas?? im tired and may be thinking crooked

 

Well I had no cat on there before. It was a straight pipe from the headers back to the trunk. Litterally no back preasure whatso ever.

 

With non-feedback induction systems, a freer flowing exhaust leans out the mixture ratio. Feedback systems compensate for that (to some extent, anyway - MAF is better about that an SD).

If an exhaust system is restrictive, it takes engine power to "pump" the exhaust out the system. Therefore, if you remove some of that restriction, less power is required so more of the power produced by burning fuel goes towards moving the vehicle. Therefore, more net power and less net fuel consumption under cruise conditions.

Apply the same principles to WOT operation, and a free-flowing system will use more fuel - true.

 

That makes sense!!!