Some questions about exhaust piping

B

baias6230

Member
Car
2009 FX35
Name
Octavian
Hey, guys. I would like to ask you a few questions about the piping diameter for my exhaust. I have installed a Megan G37 axle-back on my FX a couple of months ago. The piping diameter of the axle-back is 3 inches, and the piping of the mid-pipe it's smaller (2.25 or 2.5 inches...?). Next upgrades that are on my list are the mid-pipe and the y pipe.
My questions are:

1. Can i go with a y pipe with two 2x2.5'' collectors that merge into a single 3" and the hole mid pipe (the same dual design as stock) with the same 3" piping connected to the axle back?

2. Are there any downsides? I mean, i have red that 3" piping is pretty big for NA engines, but would this configuration work?

I could go for a mid pipe that is 2.5" thick but i have seen that most of the y pipes (that work on a AWD FX) have a 3" single exit and i thought it will be good to mantain the same diameter after the y pipe.

Thanks in advance.
 
1) Yes. The Megan Racing Y-pipe, among others, is dual 2.5" in, 3" out.

2) The NISMO cat back exhaust for the NA 350z is 3" from the Y-pipe all the way back to the muffler. One downside, albeit remote, is that by going with a 3" exhaust you may trigger the onset of Awesome Overload (AO) which on some cases could lead to a financial vortex from which you'll never escape.
 
1) So you say i should go with this setup? with the 3" mid pipe?

2) I am afraid i don't understand what you are trying to say...:tongue (2):
 
The collector from the mid pipe is 3" and the pipes running from it to the muffler are also 3"... Can this be a problem in terms of performance? The collector and the pipes having the same diameter?
 
baias6230 said:
The collector from the mid pipe is 3" and the pipes running from it to the muffler are also 3"... Can this be a problem in terms of performance? The collector and the pipes having the same diameter?
Click to expand...

I'm not sure if it could negatively affect performance in ANY way, but like I said before, the NISMO exhaust is 3" from the collector all the way back to the tips, so it can't be that bad... :dontknow:
 
Inlet in y pipe of OEM is 2.25 inches and goes to 2.5". Only y pipe that does that is a few kakumei ones but the ones left are all 3" out.
 
So in the last months i talked to a guy to make me a custom exhaust from the cats to the muffler but he does not return my phone calls so i think the custom exhaust is now history. I am going to buy some hfc and y pipe in the spring and i would like to know a few things about the y pipe. The one i would like to get has 2x2,5" inlet and 3" outlet. The stock midpipe is 2,5" or 2,75" from my understanding.

Would it be a big problem if i would mix (for now) the y pipe 3" outlet with the 2,5"/2,75" inlet from the midpipe in terms of performance?
I know it's not good to go from bigger to smaller but i saw some people with Z's and G's that are running aftermarket y pipe with stock exhaust.
 
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baias6230 said:
...

Would it be a big problem if i would mix (for now) the y pipe 3" outlet with the 2,5"/2,75" inlet from the midpipe in terms of performance?
...
Click to expand...

The stock cats are by far the biggest restriction in the OEM system. Replacing them will help performance. Probably not much on their own, but when you get the full system installed they will wake up a bit more. The improved y pipe collector will help scavenging if its well designed (not an ebay special). If not, then it just wont... The piping diameter increase that close to the motor probably won't have any effect at all as you'll still have the stock mid pipe and rear section stopping things up downstream. You'll want to avoid big diameter increases after the y pipe though, because larger pipes make for cooler exhaust temps and slower moving gasses, both of which hurt performance.
 
I talked to the guy who's making my custom exhuast and i will take this route. I decided to not go with a true x-pipe configuration and stay with the y-pipe configuration. I will buy a G37 y-pipe and make him do just a custom 3" mid-pipe to the muffler. I have a question now...
Should i go with resonators like the stock system uses or can i put a straight trough muffler instead? (note that i will buy HFC's soon)
I know what a resonator does and what a muffler does and what's the difference between them but i would like to hear what you guys think in terms of sound. I heard some 350z's with custom x-pipes configuration (using magnflow x-pipe muffler) and sounded pretty bad ass... deep and somehow retaining that VQ sound.
Thanks in advance!
 
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baias6230 said:
...
Should i go with resonators like the stock system uses or can i put a straight trough muffler instead? ...
Click to expand...

Right now I have headers, hfc's, a dual 2.25"->3" y pipe, and 3" all the way back. This system started without a resonator (way too loud+drone), then I added a resonator (a little too loud and less drone), and now I have a straight through 5x9x14 muffler in place of the stock resonator (quieter and no drone). Its still way louder than the OEM system but not by much....until you hit the gas. ;)
 
So, tchuck you say this is a way for a more temperate street exhaust? With a muffler instead of a resonator?
 
Ok, so i met with the guy who is buildind my custom exhaust to take measurments for my flanges. I will do 2.5" piping (the guy says that's the diameter he would run on this engine) from the cats to my Megan Axle Back with a Magnaflow Resonated X-pipe after the cats. The thing is i love the way my FX sounds just with the Megan axle-back... It's not too deep and has a nice growl.
Right now i am scared of two things:

1) I don't want to change the sound too much.... Do you guys think it will be loud and it will lose some of the VQ harmonics? I am afraid it will be too loud and obnoxious, tough i have seen some videos of some G/Z's with the Magnaflow resonated x-pipe and sounded awsome!

2) What will happen to the low end torque? I drive my car mostly trough town so i am thinking low end torque is better. I also do not have a tune option and i don't want to put the exhuast and what any other mods i may bring to it without a good tune.

I know that the exhaust designs are specific for every application but i need some help from you guys.
Thank you!
 
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So you're doing dual 2.5" tubes from the cats to the rear section? Any resonators aside from the ones on the x-pipe?
 
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