Ok, so I went to my local muffler shop to do some custom welding and what not.. and he tells me that I have "no back pressure".. causing my muffler to sound like crap (choking, chugging, farting). I'm N/A -- stock header, zpi s-pipe 2.5", tsudo n1 2.5" catback --, and he said that i'm losing power due to the "no back-pressure" business with the whole 2.5" piping.. ASIDE from being auto, I guess I can feel the LACK of power kickin' in. So, he tells me that 2 1/4" would be ideal.. and he recommended me to put the STOCK mid-pipe back on..

What do you guys think? a 2.5" (s-pipe) to 2 1/4" to 2.5" (tsudo n1 axleback) doesn't sound bad at all.. would there be that MUCH of restriction by putting the stock midpipe back on bolted with the 2.5" pipings at each end?

I might be adding a header later on, so would the header increase back pressure making the straight-through 2.5" s-pipe/midpipe/axleback useful?

I'm considering putting back the stock midpipe on for now and putting the tsudo midpipe back after adding a header, but wanted to make sure with you guys first if I should leave the tsudo midpipe since I'm getting a header..

Thanks in advance!!

 

Tell him he needs a new job. I'm so sick of hearing this.
If you have the stock header, you have the biggest restriction in the stock cat.
I have 2.5" all the way back and the car feels great.

 

Get a supercharger or a turbo and 2.5" will be perfect!

 

haha, i quote you on that one bro.. foreal though. that's what i thought.. but if I add an Aftermarket header, wouldn't that worsen the back-pressure even more? will adding a resonator (which i will most likeley do to eliminate rasp) get some back-pressure back?

titolito, is it true that a s/c or turbo will enhance the sound of a catback? it will sound much "smoother"?

 

Your mods did not result in a loss of power. The only way adding an exhaust might end up losing power is if it was 4-inches from the collection manifold back.

Back-pressure is always bad. This is what you remove by adding an exhaust in the first place. The tradeoff is, if you make the exhaust path too big, the exhaust gasses will cool off too much before exiting, resulting in increased densities and backpressure.

I don't think you need to change anything back to stock.. spend your money moving FORWARD with your build.

 

Ugh. Misinformation theater. "Back pressure" is a meaningless term in terms of exhaust setup. The only thing that need be focused on is exhaust velocity.

Yes, that 2.5" piping is causing you to lose power. The motor isn't pushing out enough air to fill that pipe. So what happens? The exhaust velocity slows down. The variance in pressure between the exhaust ports and the tailpipe is now less than it would be with a stock exhaust setup. So except for a fingernail thin sliver of the powerband where you're making bigger numbers, you're now down on power through 90% of the band or more.

The motor will never force out enough air to fill that big pipe, unless you cram more air into it to begin with. The bigger pipe has slowed down the exhaust gas, cooled it off, rasped it up, and generally made a mess of a perfectly serviceable exhaust.

And no CAI or bolt-on bauble wil solve the problem. The system can only flow as fast as the most restrictive point, which will be the emissions gear, followed by the valvetrain and porting in the head.

 

I know nothing about the "sound" of any exhaust.

What I meant to convey is that a super or turbo charger will force enough air into your engine and exhaust to fill out a 2.5" exhaust pipe nicely. From my understanding(reading through these threads), 2.5" is the perfect diameter for forced induction applications on our tCs. With that in mind, get a super/turbo and call it a day.

 

heh, spend 3k+ on FI so your exhaust will sound better

 

on this car unless your boosting.. 2.5 is to much. 2.25 will be just perfect. as back pressure does play a role and these cars dont push out enough to support the huge piping.

 

i've got the draxas full kit with HPR header. No loss in power for me. Any the whole thing about "losing" torque/hp depends on how you define "losing." You don't "lose" power as you up the pipes, but it does move further up the power band. One poster was correct about how larger piping prevents exhaust from flowing quickly. This is compensated at higher speeds where the bigger pipes actually help you increase your velocity. The only problem is that this idea works great for big V8s and old muscle cars b/c they are built to just go for the redline and keep pushing. Our I4 is nice and torquey but is very limited in stock ECU setup. We produce our power at 4000-5800 Rpm. If we push that any further up, we'll be in the redline and I am almost 100% that we are rev limited at 6700. That is where you can say you "lose" the power b/c it's just out of reach due to limits put upon us by our own ECU.

 

our redline is 6250. moving the powerband up would hurt's us that much more because of it.

 

Agreed.......get the CamCon and adjust the VVT-i for lower power bands. Much more fun. Who all is going to try topping out their car in a race on a highway with a tC? We stop at 127 so it's no point. Just beat the cars from 1st-4th and let them pass you out of frustration in 5th.....haha