thats what a cut out is for. lol. but most people dont want to get one for some reason.

 

I remember putting my stock dp for inspection and had major fluttering, surge, during cold start ups do to back pressure, until put my catless back on.

 

if you think about gases coming out of your turbo, needing a certain amount of room. It doesnt make much sense to me that they would need the SAME amount of space the ENTIRE way through the exhaust system, they are cooling dramaticaly and needing less space. does it make sense that we need that same amount of space for gases that are 1/2 as hot? I wouldn't imagine so. this is just my educated opinion tho, i could be wrong.

 

which is my point...why would you not want a 3" then...it would in theory flow more.

 

then you lose psi, but put less stress on the motor with no back pressure. I hear the same thing from a muffler shop if your running a turbo or supercharged you need back pressure. Still can't believe Agency Power marked their catback down to $400, it used to be in the $650's and higher depending on vendor.

 

cutout is way too much for the stock turbo, 3" flows better. someone one here lost hp i dont remember the thread.

 

I can see this debate go out all day. I'm can see either MPx, ZZP, Dejon jumping in to straighten out the confusion.

 

sooo you want back pressure in the exhaust system to try and make the turbo not spin? I thought everyone wanted free flow do you see where there is confusion?

 

I want back pressure to keep my turbo spinning and maintain boost pressures. I'm not planning for a bigger turbo. If I was, then 3" to get free flow from the back pressure to put less strain on the motor is the way to go if your running 50 trim or higher.

 

how does back pressure keep your turbo spinning? exhaust leaving your turbo keeps it spinning....back pressure would want the wheel to spin the opposite way....

 

I'm about to quit guessing here and just go 3" and be done with. I'm already confused.

 

Seeee this is what I mean. People I dont think understand right.

You want high velocity from the headers to the turbo, to keep the turbo spinning. you want ZERO back pressure in the turbo back, so that there is enough available flow for the turbo to just push as much exhaust out as it can. Hence why I am a fan of the 3" or no exhaust...and question why everyone wants 2.5"...as by turbo engineering folks, it does not make sense to have a small exhaust system on a turbo...

250hp and sub 300whp a 2.5" is fine
300+ Imo a 3" is needed

 

Until you get on it, than it sounds just plain nasty. MPx is similar.

 

Northvibe, your my buddy and usually mind twin, but i put down 310/360 with just a hahn intake and modpipe with catless mid section and stock exhaust. (On an average/conservative BYT tune) However, if I wanted more, I would go 3" exhaust to speed up flow, and decrease backpressure and temps, and to remove my 3"downpipe to 2.5" exhaust bottleneck

However I agree with you, a 2.5" aftermarket exhaust is pointless, your stock is 2.5". If you really wanted just hack off the muffler, or get a cutout. *I have a cutout on mine, but I have to get the motor yet*. Im debating getting an mpx 3", but I think BYT is making one so I might test fit his.
Also, everything you have said about back pressure here is trooof. Any turbo racecar in any serious racing uses cutouts or like 1 foot exhaust dumps out of the turbo aka no exhausts. I would say they know what they are doing.

OP, do not buy an exhaust before you buy a downpipe. The downpipe will change the sound good enough, and give you better gains and feel.

 

a cutout would flow more because it ends right after the downpipe. the exhaust gasses havnt cooled that much at that point so they are still expanded and require the 3" diameter in the exhaust. in a catback, they cool after the downpipe, thus needing less space since cooler air takes less room than hot air. with a 3" exhaust, you have a lot more room that is wasted with more cooler air. a bigger pipe will flow more but if its filled with dense cool air, the engine will use the same amount of power pushing it out as a 2.5" diameter exhaust, resulting in little to no gains. its a little difficult to explain but u catch my drift.

back pressure is a myth. you do not need backpressure for more power. sure, youl increase your low end a little bit, but top end falls off. top end is more important than bottom end performance wise. just think, when your racing, which part of the powerband do u spend more time in, top or bottom?

a cutout is best because in a turbo car, you want to get rid of exhaust gasses fast. it does not need backpressure or anything, just the best flow possible. a cutout provides better flow than any diameter exhaust because the gasses dont have a pipe to cool in and reduce exhaust velocity, thus reducing flow.

ill add in to better explain. a 3" exhaust technically flows better, but not at our power levels on a tiny turbo such as ours. the gasses cool rapidly in the exhaust and take up less space because cool air is more dense than hot air. now, what would be harder to do, push out 3" worth of cool air, or 2.5" worth of cool air? since 3" would be more volume for cooler air, in theory it would be harder to push out since its more of it to push however, the 3" diameter allows the exhaust to still flow well, so it almost cancels out, which is why a 3" exhaust doesnt gain much power.

on a 2.5" exhaust, the exhaust velocity is faster since there is less air to push out after it cools. this means it actually flows gasses faster than a 3" however its not as big a diameter, so it flows less volume.

this is why the power gains are negligable till you go big turbo. once you go big turbo more air is expelled thru the exhaust thus requiring a bigger diameter. it all boils down to what you plan on doing in the future and prefrence.

i hope this was somewhat easy to understand

 

wait wait wait... so whats the problem with Hahn's? jus hittin the torsion beam When lowered? I've heard a couple dif exhausts on the TC (mostly on youtube..) an None of em sound as good/clean/deep as Hahns.. I Did check out a couple of em, but I didn't see anything about that. I was gonna wait for ArK's but dude said it would be a while an eh.. I wants it noWW

But really tho.. I shouldn't lower my car now or what? I was gonna order the the ArK springs(I keep putting it off ) but I don't wanna be banging around or breakin nuthin..

 

MPX is about as close as you're going to get, sound wise, to Hahn's..and the MPX one will 100% not bang around if you're lowered.

 

I already have zzp catless, k&n intake, and trifecta tune.

I am very satisfied with my performance and power and honestly i don't need any more power on my FWD drive train. Since i got trifecta I'm almost never in a situation where i can slam my pedal without destroying my tires.

I'm mainly replacing my catback as an audible upgrade and also i want a stainless system since i drive in salty conditions in the winter.

 

you might wanna order the ark springs now while they are only 199+ shipping. original price is like 300 bucks. lol.

 

bingo

 

ok you have basically the same setup and reasoning as I do than haha

 

ARK springs will be a problem with hahn exhaust i am willing to bet. I have ARK springs and the rears go pretty low. This is one of the reasons i opted out of the hahn catback. You're going to have to stick with pedders now (not like that's a bad thing).

 

Hey man Never said a 2.5" would allow over 300whp..just saying its probably not what most people would do or recommend. But ya I'm still stock exhaust w/ 3" dp. I'll be tuning this spring and I want the mpx but still am having a hard time justifying the purchase yet. But its because I'm frugal not that I don't want 3"

 

i dont have a hahn, but i think with some adjustments to the hangers you could help the rattling issue? idk, just a guess.

how are the ark springs? i have ark springs AND pedders. funny story, but pretty much if i dont like one i have the other. i like the ark for the drop tho. i could run pedders in fron t and ark in the rear with a sway bar.. hmm.

 

Ark springs handle great but feel a bit stiffer than stock. It almost feels like they are set up for track days rather than daily driving. As far as the drop i think they look perfect.