Difference in Exhaust Diameter Question
10-27-2014, 04:11 PM
#1
Difference in Exhaust Diameter Question
I've tried a few different ways of searching for an answer to this question but haven't seen anything specific.
Coupe exhaust is 2.5" in diameter and sedan is 2.25". I know that going from a 2.25" into a 2.5" pipe is not so bad but what about the opposite? For example, going from a couple, 2.5" high flow cat into a sedan, 2.25" factory exhaust. There's a quarter inch difference in diameter and even though a gasket can be used to stop leaks at the seam between the two different diameter pipes, the air flow is now hitting a lip on its way out of the system. Does that not create a point of pressure and, if it does, is that something to be concerned with? A quarter inch isn't much so it may not be a matter of concern, but I thought I'd ask for opinions on the matter anyway. I'd prefer opinions based on actual experience and not conjecture since I do that so well on my own anyway but I'll take anything you guys got.
Jeremy
Coupe exhaust is 2.5" in diameter and sedan is 2.25". I know that going from a 2.25" into a 2.5" pipe is not so bad but what about the opposite? For example, going from a couple, 2.5" high flow cat into a sedan, 2.25" factory exhaust. There's a quarter inch difference in diameter and even though a gasket can be used to stop leaks at the seam between the two different diameter pipes, the air flow is now hitting a lip on its way out of the system. Does that not create a point of pressure and, if it does, is that something to be concerned with? A quarter inch isn't much so it may not be a matter of concern, but I thought I'd ask for opinions on the matter anyway. I'd prefer opinions based on actual experience and not conjecture since I do that so well on my own anyway but I'll take anything you guys got.
Jeremy
10-27-2014, 11:29 PM
#2
If you don't plan on going force induction then getting Fast Intention Exhaust would be perfect for you since it's 2.25" in diameter. It creates a nice back pressure maximizing your performance. I had the full set up w/ Fast Intention (HFC and exhaust).
10-28-2014, 09:35 AM
#3
Registered Member
I've tried a few different ways of searching for an answer to this question but haven't seen anything specific.
Coupe exhaust is 2.5" in diameter and sedan is 2.25". I know that going from a 2.25" into a 2.5" pipe is not so bad but what about the opposite? For example, going from a couple, 2.5" high flow cat into a sedan, 2.25" factory exhaust. There's a quarter inch difference in diameter and even though a gasket can be used to stop leaks at the seam between the two different diameter pipes, the air flow is now hitting a lip on its way out of the system. Does that not create a point of pressure and, if it does, is that something to be concerned with? A quarter inch isn't much so it may not be a matter of concern, but I thought I'd ask for opinions on the matter anyway. I'd prefer opinions based on actual experience and not conjecture since I do that so well on my own anyway but I'll take anything you guys got.
Jeremy
Coupe exhaust is 2.5" in diameter and sedan is 2.25". I know that going from a 2.25" into a 2.5" pipe is not so bad but what about the opposite? For example, going from a couple, 2.5" high flow cat into a sedan, 2.25" factory exhaust. There's a quarter inch difference in diameter and even though a gasket can be used to stop leaks at the seam between the two different diameter pipes, the air flow is now hitting a lip on its way out of the system. Does that not create a point of pressure and, if it does, is that something to be concerned with? A quarter inch isn't much so it may not be a matter of concern, but I thought I'd ask for opinions on the matter anyway. I'd prefer opinions based on actual experience and not conjecture since I do that so well on my own anyway but I'll take anything you guys got.
Jeremy
Here is some recent shopping/research on Sedan exhaust: https://www.myg37.com/forums/g37-sed...t-options.html
10-28-2014, 12:24 PM
#4
out of curiosity, why not go with a full catback? Invidia, Topspeed, and Manzo are under $1000... Fast intentions, ARK, and Stillen are 1200-1500. They are direct bolt-on systems.
Here is some recent shopping/research on Sedan exhaust: https://www.myg37.com/forums/g37-sed...t-options.html
Here is some recent shopping/research on Sedan exhaust: https://www.myg37.com/forums/g37-sed...t-options.html
That said, this car came out of New Jersey before I bought it and the stock exhaust is very rusted. Putting the Tanabe mufflers on was no big deal but I may end up having to go with an aftermarket or custom exhaust setup if the bolts are too rusted. I have a lift at work and some guys that will help me with the job. Hopefully I'll have good luck swapping out the cats but if not I'll probably have to take it to a local muffler shop and have them custom make me something since I can't afford to be without my car until an aftermarket one comes in. It's a risk, I realize, but one that I'm willing to take.
I posted this because I just wasn't sure whether or not going from a larger diameter into a smaller diameter would be a bad thing. So thanks again for the input!
10-28-2014, 06:36 PM
#5
Invidia q300 now 3 years on my sedan. Exhaust is marginally louder than stock until you really put your foot into it. Daily driving attracts minimal attention. Interior noise is slightly louder than stock when cruising, just enough to let you know you're on the throttle.
No hfc's or other exhaust mods, just cat back q300.
No hfc's or other exhaust mods, just cat back q300.
10-28-2014, 07:53 PM
#6
Back pressure is bad, m'kay? Our goal is to minimize it as much as possible within our means. Back pressure is for those with carbs who don't understand how to jet them. Oh, and those cars with MAP systems. Our MAF and ECU can deal with changes we impose such as with exhaust system changes.
You would be much closer if you speak of pipe diameter versus exhaust gas velocity.
You would be much closer if you speak of pipe diameter versus exhaust gas velocity.
10-29-2014, 09:31 AM
#7
Super Moderator
Check your assumptions on the factory diameter of the coupe and sedan exhaust.
I'm pretty sure that based on the research I've done, the sedan exhaust is right around 2" near the entrance to the Y-pipe then tapers down to a little under 2" as it leaves the resonators.
I can't imagine the coupe exhaust would be that much larger as the motors are identical.
I'm pretty sure that based on the research I've done, the sedan exhaust is right around 2" near the entrance to the Y-pipe then tapers down to a little under 2" as it leaves the resonators.
I can't imagine the coupe exhaust would be that much larger as the motors are identical.
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10-30-2014, 02:31 PM
#8
Check your assumptions on the factory diameter of the coupe and sedan exhaust.
I'm pretty sure that based on the research I've done, the sedan exhaust is right around 2" near the entrance to the Y-pipe then tapers down to a little under 2" as it leaves the resonators.
I can't imagine the coupe exhaust would be that much larger as the motors are identical.
I'm pretty sure that based on the research I've done, the sedan exhaust is right around 2" near the entrance to the Y-pipe then tapers down to a little under 2" as it leaves the resonators.
I can't imagine the coupe exhaust would be that much larger as the motors are identical.
I do know that Fast Intentions (typically) makes coupe exhausts at 2.5" and sedans at 2.25" and this applies to cats and the cat-back.
I have a sedan and upgraded to 2.5" piping for the cats and CBE and couldn't be happier.
10-31-2014, 12:00 PM
#9
Check your assumptions on the factory diameter of the coupe and sedan exhaust.
I'm pretty sure that based on the research I've done, the sedan exhaust is right around 2" near the entrance to the Y-pipe then tapers down to a little under 2" as it leaves the resonators.
I can't imagine the coupe exhaust would be that much larger as the motors are identical.
I'm pretty sure that based on the research I've done, the sedan exhaust is right around 2" near the entrance to the Y-pipe then tapers down to a little under 2" as it leaves the resonators.
I can't imagine the coupe exhaust would be that much larger as the motors are identical.
Back pressure is bad, m'kay? Our goal is to minimize it as much as possible within our means. Back pressure is for those with carbs who don't understand how to jet them. Oh, and those cars with MAP systems. Our MAF and ECU can deal with changes we impose such as with exhaust system changes.
You would be much closer if you speak of pipe diameter versus exhaust gas velocity.
You would be much closer if you speak of pipe diameter versus exhaust gas velocity.
Yes, those are not factory diameter exhausts for Coupe/Sedan. The sedan crimps down to under 2" at some points.
I do know that Fast Intentions (typically) makes coupe exhausts at 2.5" and sedans at 2.25" and this applies to cats and the cat-back.
I have a sedan and upgraded to 2.5" piping for the cats and CBE and couldn't be happier.
I do know that Fast Intentions (typically) makes coupe exhausts at 2.5" and sedans at 2.25" and this applies to cats and the cat-back.
I have a sedan and upgraded to 2.5" piping for the cats and CBE and couldn't be happier.
11-02-2014, 12:53 AM
#10
Registered User
twin_snails, hey matt... how much louder is your car since you went with a 2.5" exhaust than stock? I'm interested in upgrading but I'm not wanting something that is loud. I've outgrown that part of hot rodding with my DD...
thanks Doug
thanks Doug
11-02-2014, 10:54 PM
#11
Hi Doug, mine is definitely a lot louder than stock, but my X-pipe has no resonators on it. I would go with a Fast Intentions setup with the X-pipe with 18" resonators. That will damp the sound from where mine is at. It will give you a nice increase in performance and a nice tone as well. 
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