Exhaust Options: Is It Better To Keep This Big One Or Go Back To Standard?

[Houdini]

I'm faced with a choice at purchase time: keep this aftermarket exhaust that's on the car or go back to standard muffler and exhaust.

I'm not certain exactly what this exhaust is. Is there any issues with such a thing or is there a disadvantage in going back to standard?

p.s. I realise I'm a bit light on detail sorry.

Edited April 17, 2009 by Houdini

[66yostagea]

Hey Houdi

My stocker had a 21/2 cat back that was very quiet. Got a 3" jj bell, Xforce Hiflo Cat and 3" cat back, Sounds a bit loudish but you can feel the extra get up and go.

[Califunky]

standard exhausts are generally very restrictive and take a convoluted route under the car, a well designed aftermarket exhaust with a larger bore will have a more direct route under the car getting rid of waste gases more effectively reducing heat build up and helping release a few extra ponies - obviously getting rid of the cat is going to benefit massively

They sound good too

[Houdini]

standard exhausts are generally very restrictive and take a convoluted route under the car, a well designed aftermarket exhaust with a larger bore will have a more direct route under the car getting rid of waste gases more effectively reducing heat build up and helping release a few extra ponies - obviously getting rid of the cat is going to benefit massively

They sound good too

I had read though that turbos benefit from back pressure and a too big exhaust is detrimental. Is that way off?

[Califunky]

I had read though that turbos benefit from back pressure and a too big exhaust is detrimental. Is that way off?

They do need some back pressure yes, i believe a 3" pipe max is the way forward. I am currently running a 3" turbo back system which makes the car sing and has helped improve throttle response

[KiwiRS4T]

No, back pressure is largely a myth. A turbo compresses air and after the compressed mixture is ignited the resultant expansion pushes the piston down and then has to go somehere hence the need for a big exhaust. If yours is too noisy add a resonator or otherwise modify the system but reducing the diameter is not a good idea. If for any reason you don't like the big pipe sticking out the back (although from your photo yours looks OK to me) get a twin tip.

[Califunky]

Quick comparison shot for you

standard v nismo

You can see the nismo exhaust has a much smoother route - no sharp bends to disrupt airflow and a bigger bore

[xRHETTx]

Just saw in your other thread Califunky that those exhausts are for a C34 Stagea. Houdini's looks to be a newer M35 Stagea.

And turbo charged cars dont require any exhaust backpressure (unlike NA cars where it (can) help with cylinder exhaust gas extraction.)

[RBPOWA-(TJ)]

c34 m35 , think th point was about the smoothness of stock to aftermarket.

my opinion M35's with cannon's look like shit, go for a xforce rear muffler #MP01, also go the 3inch all the way, i had a second muffler on mine also couldnt hear a thing it made 140.2kw up from 116kw have since taken out the mid muffler so i can hear it

http://www.skylinesaustralia.com/forums/10...image70834.html

[mattye]

Back preassure is important no mater if the car is N/A or Turbo Charged.

Think of it as a garden hose (without a nozel). The water just flows out slowly, but if u put ur thumb over the end a bit the water comes out quicker. Of course at the same time if u cover it with ur thumb too much then the water slows down. Its realy about finding somewhere in between.

Rule of thumb with a Turbo Charged car is wroughly 3" or 3 1/2".

Also another thing, with Turbo Charged cars is if u go too big u can experiance whats called compressor surge. Think of it as a Turbo back firing, and results can include a new Turbo.

Anyways Houdini in my opinion stick with the aftermarket exhaust and replace the rear muffler with a stainless twin tip.

Edited April 18, 2009 by mattye

[KiwiRS4T]

Back preassure is important no mater if the car is N/A or Turbo Charged.

Think of it as a garden hose (without a nozel). The water just flows out slowly, but if u put ur thumb over the end a bit the water comes out quicker. Of course at the same time if u cover it with ur thumb too much then the water slows down. Its realy about finding somewhere in between.

Rule of thumb with a Turbo Charged car is wroughly 3" or 3 1/2".

Also another thing, with Turbo Charged cars is if u go too big u can experiance whats called compressor surge. Think of it as a Turbo back firing, and results can include a new Turbo.

Anyways Houdini in my opinion stick with the aftermarket exhaust and replace the rear muffler with a stainless twin tip.

Bad example. If you stick a nozzle on a garden hose the amount of water passing through will either remain the same or become less (regardless of the speed of the water coming out of the nozzle). People don't spend $1000 on extractors and then look for ways to create back pressure. Effectively back pressure is as unwelcome on a n/a car as a on turbo.

[_Ryan_]

Back preassure is important no mater if the car is N/A or Turbo Charged.

Think of it as a garden hose (without a nozel). The water just flows out slowly, but if u put ur thumb over the end a bit the water comes out quicker. Of course at the same time if u cover it with ur thumb too much then the water slows down. Its realy about finding somewhere in between.

Rule of thumb with a Turbo Charged car is wroughly 3" or 3 1/2".

Also another thing, with Turbo Charged cars is if u go too big u can experiance whats called compressor surge. Think of it as a Turbo back firing, and results can include a new Turbo.

Anyways Houdini in my opinion stick with the aftermarket exhaust and replace the rear muffler with a stainless twin tip.

the turbo IS the back pressure... if you think they need back press so bad how come they run so much better with just a dumppipe, nothing else?

NA car= dont go too big, turbo= less restrictive the better

i have two oval mufflers on a full 3" system, legal noise, flowy, bum dyno noticed it,

[BensDR30]

Turbo performance = the biggest pressure difference you can get across the turbine. Further to that, you are aiming to convert the turbulent flow into smooth linear flow - which is why a rather large dump is desirable (as is a large exit from a Cat converter).

Exhaust back pressure on a turbo engine = reduced performance (and possible increase in turbo wear).

Tuned (read minimal to do the job) back pressure on a tuned N/A manifold is there as part of the tuning/extraction physics. If you can get good extraction with the right length primaries and no back pressure you have a winner.

Have a read of the books 'Forced Induction Performance Tuning', 'Turbochargers' or 'Maximum Boost'.

Edited April 18, 2009 by BensDR30

[910trx]

yup back pressure is usually there to aid scavanging of exhaust gases post combustion

and this is important to get just right in a na car

exhaust gasses at the right pressures and pulses can create vacumes and low pressure points that essentially aid the extraction of gasses.

a perfect sized exhaust diameter in a na allows the free flow of gases out the exhaust at a constant rate rather than creating gas back ups.

turbos are different as there after the manifold is a massive obstruction which unless on overrun with heaps of spool will always produce pressure to a certain extent as it is forced through the fins.

after this you want to get rid of as much pressure and turbulance as necessary

yes the same theories can be applied to turbo as na but back pressure is not only dictated by exhaust diameter but more importantly exhaust manifold design, good exhause manifolds dont just try to maintain equal pipe lengths to aid better spooling but to enable a better eficiency in the escape of gas from the combustion chamber to the turbo.

my take on the original question.

if it has an exhaust on it, keep it on there to avoid paying coin later, if you dont like the tip then change it but i vote for keep the bigger exhaust

Edited April 20, 2009 by 910trx

[zei20l]

i think you should swap your bigger exhaust for my stock one. i wont even charge you

but seriously, keep the larger one youll have more power. but downside is it will be noisier than stock. but if you dont like it, i got dibs on it, ill even come to canberra for it

[iamhe77]

I'm faced with a choice at purchase time: keep this aftermarket exhaust that's on the car or go back to standard muffler and exhaust.

I'm not certain exactly what this exhaust is. Is there any issues with such a thing or is there a disadvantage in going back to standard?

p.s. I realise I'm a bit light on detail sorry.

Keep it!

If it is a 3" exhaust, get a matching size front pipe. The less restriction on our turbo the better... believe me!.. unless you want an excuse to HiFlow/replace your turbo.

No point (sound excluded) in having the restrictive stock front pipe (cat) with a large cat-back exhaust.

Got any pics from under the car? Would like to know which system you have (looks familiar) and if you also have a 3" front pipe.

[_Ryan_]

i would change the rear muffler for a nice SS magnaflow oval one... i can take a photo of mine when the mrs brings my car back if you want

[mattye]

Hey Guys I think u all took what i said way to litteraly. I'm not saying that u should have a tiny exhaust. I was just pointing out a common mistake made by alot of people who are under the influence that the bigger the better. And although most of the time it is. There is a point when bigger stops being better.

But at the end of the day think about it...there is a reason even drag cars still have exhaust pipes.

[BensDR30]

Quite right - there is certainly a point of diminishing returns, and increasing visual silliness

[mattye]

Well put Ben.