3.0si muffler / back box delete, video + pics attached!

[jevans]

Hi,

I've had my z4 for a month now but have seen plenty of videos on youtube of the backbox delete but i can't make my mind up between that and the secondary cat delete for noise. Have you noticed much loss of power with the back box delete?

cheers,
James

I'm also deciding on what route to take. Quick Car Reviews on YouTube has made me seriously think about just deleting the secondary cats. As long as it doesn't sound like a Corsa with a powerflow exhaust I'll be happy.

I've contacted Alex from that channel and this is his response -


"Alex I'm booking my car in for a chop next week so I'm in the final stages of deliberating..... How much louder than the stock exhaust in this setup in real life. Both on idle and town driving and then full throttle. Cheers!"

Quick Car Reviews 4 days ago
+James Evans Hi James. The only time you'll ever notice a difference is flooring it (good) and occassionally if you put the foot down a bit at low revs it rumbles a tad but I honestly don't notice it. On the motorway cruising at 70mph or thereabouts it's absolutely fine. Honestly, it's only if you're asking a lot of the engine that it gets louder. I had a muffler delete and that was awful so I had the muffler back on and had this done. I've just asked my girlfriend and she says she "does not find it annoying at all." Although she has now found out that my car isn't quite as environmentally friendly as before...


maybe this will help you decide

 

[Newbers]

Anyone know of a garage around St Albans that might be willing to do this? I called EMP Performance (a "dedicated state of the art Custom Exhausts company") in London Road thinking they would be perfect but they weren't very keen....

 

[Disca]

I had this done at style dynamics in hayes, with a flange so that I could switch between the original box and straight pipe, as it really did get too much after a while.

 

[Newbers]

I had this done at style dynamics in hayes, with a flange so that I could switch between the original box and straight pipe, as it really did get too much after a while.

Thanks. When you say flange do you mean a valve to close them off?

 

[Disca]

Nope, meant the pipe between the backbox and normal exhaust parts had a flange made of two square plates that screwed together. Meant you could change between the backbox and straight pipes by jacking the car up and cursing many many times. We only did it once and it was a hassle.

 

[ba3bas]

Why is anyone concerned with torque if removing the backbox?

Unless you start changing the manifold and the pipe diameter of the exhaust system front to back then thats when you need to consider whats best for performance.

If youre just removing the backbox or even swapping all it will do is release gasses faster which with our shoddy maifolds is a good thing.
Maybe a small increase in hp but no adverse affects.

The reality is though, any mods to a car should be followed with a custom remap to take advantage of any mechanical improvements.
That being said its not worth doing that unless you have other plans like induction, cams etc

 

[Disca]

Funnily enough I found removing the backbox to slow the car rather than speed it up ba3.
It suffers from a lack of back pressure and you can hear it suck air back up the exhaust as the revs get close to idle.
Did make a difference to how it drove as I noticed it everytime I put the backbox on again.

 

[Machine monkey]

I have a straight through exhaust. Even though it dose have a muffler. But mine dropped mpg and felt sluggish but when I put a K&N filter on mpg went back to normal and it felt quicker.

 

[ba3bas]

Funnily enough I found removing the backbox to slow the car rather than speed it up ba3.
It suffers from a lack of back pressure and you can hear it suck air back up the exhaust as the revs get close to idle.
Did make a difference to how it drove as I noticed it everytime I put the backbox on again.

Back pressure isn't a good thing all the time.
On NA's it helps to cover shite header design and collectors but properly designed exhausts don't need any. What is important is keeping an adequate exhaust gas velocity, but that's different.

Either way with our cars to make any performance improvement is in the manifold/headers.

Since we can't really get equal length headers since the steering rack is in the way, a decent custom job with a collector (essentially a one way valve) will do a good job of clearing gasses.

Edit - extracted from more reading online and supports my requirement for remapping I guess...

As I understand it, well tuned NA or SC engine exhausts use the kinetic energy of the exhaust gas from the previous cylinder to create a partial vacuum in the manifold at exactly the right moment (this is called exhaust gas scavenging); this isn't really possible on a turbocharged engine because the turbo restricts the exhaust gas flow too much. Thus in a turbocharged car, you want the air to simply flow as freely as possible to the exhaust outlet; however, for other engines back-pressure is used as part of the tuning technique to align the pulses correctly, so fitting a freer flowing exhaust to a N/A car can actually reduce power