exhaust needed or no?
 

OK not super important, but more of an " I'm curious" question. I have a k&n to put on, and I alr2any installed my header( stock replacement from ottp) I think most call it a shorty. The thing is I only have the exhaust that was on it. And I believe it is stock as was everything else pretty much. Is there a big difference with how effective the k&n will be without having a magnaflow or Borla or gibson on there? Or is the header going to make a big enough difference without getting a new exhaust system?
I assume new would be better flow just didn't know how big, eliminating the cat is pretty good I thought. And I am obviously gonna put it on regardless but curious. And knew there would be someone with enough exhaust knowledge to pass on some good info.
Thanks guys inadvance

It's incremental. Everything helps, but it is in no way required.

In dyno tests, I can tell you adding a K&N filter alone does virtually nothing for the I5s, so regardless of exhaust, a performance filter is an almost nothing.

Adding a CAT back exhaust by itself, also does nothing, but it can get you some sound if that is what you are looking for.

Like Larry said, its all incremental. To take advantage of a high flow filter, you have to ditch the OEM intake and its resonator box and install an intake. K&N would be one of my last choices (unless you are looking for a warm air intake and drive only a street queen). Add a PP TB for more. If you can breath more in, then you have to make accommodation to flow it out. So if you have the replacement OTTP header, it would be better to match it to a free flowing exhaust. Then get a PCM tune to adapt to the new potential.

Add an Efan conversion anytime.

You can drive it just the way it is, but you still have more mods to do to.

I have read a lot of your posts about all of the mods mentioned and all of the good test results as well. I was going to get one of your intakes Doc, but got a really good deal on the 77 series. I do drive about 95% on roads with it, only hunting season or if visiting somewhere also or camping. No real offroading as there aren't many places here unless you have something unreal in clearance that fits in ATV trail. I also plan on kinda doing as yours does and reuse the airbox with k&n and thought of trying to make the inlet in the box larger and wrapping the tube to insulate it, as I read your reviews and many others about the k&n. I plan on more mods later but not enough cash right now. I just dropped about 1800 in parts maybe a bit more. Gonna have to wait until next tax season unless it is a necessity. Needed a new rad, and exhaust manifold so the header Josh price matched for me shipping included, studs, and shocks bilstein 5100 , and belt, tensioner, and an oil change ,All but k&n was needed. I get pretty good mileage already but any improvement will help. I think the previous owner neglected it mechanically or the dealer was useless he took it to.
Back on track, I believe from your post Doc that I wont get any benefits or improvement with my k&n using my current exhaust? Guessing the flat spot and the resonator as well as the muffler restrict flow too much for improved flow to work?
So the ported TB has a bigger inlet I assume to allow higher volumes of air? So having these is possibly beneficial to my engine, but at the same time, to optimize or really to have any improvements I need the rest of the mods?
Thanks for the replies

I run the OTTP stock replacement with a Gibson cat-back, and the sound alone was worth the investment. I get compliments on the sound all the time

Sound is good I guess. I haven't heard any cat backs impersonal, just on YouTube. Some sound good and some dont. We will never have the v8 rumble like the alpha. But there is nice sounding red Colorado with a turbo sounds prettygood. Also some magnaflow sounded good also.