Ok so I've done so many variables with cats, mufflers, x-pipe, h-pipe, straight pipe.. true dual or single in dual out.. but this is all talking about the best set up without killing the bank. What i really need to figure out is horsepower gain/loss, mpg difference, backpressure, ox sensors, check engine light and all that. FOR EXAMPLE; right now all four cats are hollowed out but the stock muffler still remains, is this hurting my performance? Ive tried to gather info through this site (being the reason i joined)(and am happy i did by the way) as to where to go from this point. If start with the two front (smaller) cats with magnaflow- eliminate the rear (larger cats) and run true dual flowmaster 44 series out the back, will this kill my horsepower? How about sufficient backpressure? What if I had an X-pipe in between? Any advice would help.. Thanx.

 

well i do know that i went no exhaust at the cats and f'd something up so x that idea first off.. now im running a 3 inch back from both cats to a si/so cherry bomb single chamber muffler and running it out behind the rear wheel at stock location with a rolled 4 inch tip looks sounds good and tomorrow im putting an electric cut out in between muffler and cats...

 

1997 F-150 with Borla cat back and all cats in place dyno'd 12 more HP. The stock cats flow very well. When you hollow out the cats you actually slow down the flow of exhaust gas because it now has to fill the chamber you created in the cat. Back pressure is a myth. You need flow to scavenge the exhaust gases. Find the least restrictive exhaust that will not slow down the flow you can and install that. If you look at the pipes in your truck you will notice that the overall diameter is 2.5 inches. Look at the Y section. It slims down where the pipes join. Look at the bend right after the exhaust manifold. It slims down to 2.25 inches. I have JBA shorty headers with the front cats removes and replaced with 2.5 inch pipe. Stock 2nd cats going into the 4.6 Y pipe followed by a Borla SI DO that exits in front of the rear wheels. When funds permit I will be replacing the whole thing with OBX long tube headers. It comes with all the piping to reach past the Y. It is all mandrel bent. Here is an example of the system. http://cgi.ebay.com/ebaymotors/OBX-E...Q5fAccessories

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