Bigger increases will come from eliminating the stock y-pipe if you have one, and going with a high flow cat and cat back. Headers by themselves don't make a huge difference.

 

im not sure if my y pipe is stock or not, it doesnt seem like mine is like what every body talks about theres being. see i already have one of these, from when i planned on doin 3" from the manifolds...

 

not to sound like a jerk, and i understand you're wanting to do it right- but you're also making it harder than it is.. which is easy, because there is a heckuva lot to know about exhaust systems, but pretty much in theory only.. actually doing it is easy..

ANY back pressure is bad.. people confuse back pressure with scavenging. scavenging is good, and is the brass ring, so to speak.. scavenging is heat related, and is created by low pressures of hot air.. after the energy created by the piston pushing that pulse out is expended, you're relying on vacuums created by heat to move the pulse out of the way of the next one- and hope the pistons pressure isn't solely responsible for pushing all of those wads of air out..

back pressure sometimes allows faster revs.. you know why? the engine isn't clearing all the exhaust.. if it's open at the manifold, or has a nice chamber (pipe) to go into it doesn't have to share space with other cylinders (headers) , it clears the spent air and therefor gets a nice clean sip of air to replace it.. depending on how well your heads breath, distance your valves open and for how long (cam), and how much air can fit through your intake- you can get by with really big pipes..

too open a diameter, and the pulses cool to fast, which creates a barrier for the pulse behind it, which creates back pressure..

too restrictive a diameter, and the pulse can't get out of the way fast enough for the one behind it..

fluctuations in pipe size creates changes in flow.. you want smooth flow from exhaust valve to tips..

catalytic converters are restrictive, but they are also hot, and are designed to be hot.. which tugs on approaching pules by creating an area of low pressure, and helps maintain velocity.. because of that little happenstance, a good high flow cat is beneficial almost as much as it hurts.. in vegas terms, it's almost a 'push'..

chambered mufflers are restrictive, baffled generally aren't..

all of that holds true with any exhaust system..

specific to our OE:

the manifolds are about as good as shorty headers.. the restriction is the Y.. you can do what you want to the exhaust, but if you don't address the Y you may as well not be doing anything to it..

long tube headers are a different story.. they do good for us.. curiously, the OE Y has to go if you do LT's..

the OE primaries are 2 1/4".. if you run duels, don't exceed 2.5".. if you do a Y, don't exceed 3", and only after the Y..

the sweet spot seems to be between 2.25 and 2.75".. If you go with bigger tubes, you'll want to wrap them to insulate that heat inside them.. if you go with smaller, you'll be good with how they are.. no matter what though, if you don't address that Y you'll be wasting your time.

 

youre talking about the headers with this correct? so if longtubes were the case. i would run them then to an aftermarket y and that would ultimately be the "best" thing that can be done as far as exhaust to these guys?

 

I believe he's referring to downstream of the y pipe. With the stock internals 5.2L (no race cam, turbos etc) you'll probably want to land somewhere in the 1.5" primary, stock mid pipe, and 2.75" cat plus cat back. I went with a 3" cat and catback on my 5.9 and really like it. I think there are a couple guys here running a 3" cat plus cat back on their 5.2's and like it too. I think as drewactual says the biggest problem is the y.

 

well will 3" cat back honestly be too much? i mean i could 2.75" but 3" will probably be easier to get ahold of. what is my stock y pipe supposed to look like?

 

Sorry man. I can't really comment since I've never tried it with the 5.2L myself.

 

i currently run open headers (which have 3 inch collecters) but here soon im gonna have a shop make me an exhaust. if you get longtubes ive heard the best thing to do is reduce them to 2.5" put in a y-pipe and after the y you can open it back up to 3 inches. but i have a 5.9 not a 5.2

 

Guess that leaves the question, if your gonna run dual exhaust, which is better X or H pipe?

 

nope, no dual for this guy!! but i am interested in looking into these headers but then again might not have enough $$ for all that...