Z4 Custom Exhaust

[jevans]

hi guys,

anyone recognise this car or have any idea what sort of exhaust setup has been installed?

https://www.youtube.com/watch?v=vGYxAzoDjWg

thanks

 

[mr.tourette]

no idea.. sounds good tho

 

[ben g]

He seems like he's in a rush :lol:

 

[csl1973]

I'd say a back box delete

 

[ba3bas]

Straight through exhaust that.

Drone must be killer but if you want loud...

 

[skelters]

Is that a jogger or a dogger at 0:15?

 

[jevans]

it's got the rumble of BB delete but then there's the rasp which i've not heard from just a delete so i suppose a straight through makes sense.
on the M54 would that knock the performance quite a bit? i've heard a few guys claiming to notice about half a second to 60 without a backbox

 

[pokeybritches]

There is no change in performance. Ask anyone that claims there is to try and explain what backpressure is, and how it could ever be useful to have pressure resisting exhaust flow. Then have them explain exhaust scavenging.

Backpressure ALWAYS hurts performance. Scavenging helps performance. Backpressure is a byproduct of scavenging, because a smaller diameter pipe will have increased exhaust velocity but cause more fluid friction (limiting max flow). Cutting off the pipe is like having an infinitely large pipe. The forward sections of the exhaust is where it really matters, especially in the headers. By the time you get to the muffler, all scavenging is done and you can do as you please.

 

[jevans]

I'm no mechanic so i have to take what your saying for granted so in theory removing the backbox should increase air flow thus improving engine perfromance?

 

[Yorkie Z]

I'm no mechanic so i have to take what your saying for granted so in theory removing the backbox should increase air flow thus improving engine perfromance?

It will sound s**t mate. Look up bypass pipe on here.

 

[Ed Doe]

As above - If you use your car for anything other than trackdays it will be horrendous - I chopped my backbox off and regretted it instantly. Don't get me wrong it was hilarious on a hoon, but at anything below 3k it was just way way too boomy. Made my delicate ears hurt :lol:

 

[mr wilks]

There is no change in performance. Ask anyone that claims there is to try and explain what backpressure is, and how it could ever be useful to have pressure resisting exhaust flow. Then have them explain exhaust scavenging.

Backpressure ALWAYS hurts performance. Scavenging helps performance. Backpressure is a byproduct of scavenging, because a smaller diameter pipe will have increased exhaust velocity but cause more fluid friction (limiting max flow). Cutting off the pipe is like having an infinitely large pipe. The forward sections of the exhaust is where it really matters, especially in the headers. By the time you get to the muffler, all scavenging is done and you can do as you please.

That sounds convincing but it contradicts what our own "Beetlegav" found to be fact :?

http://www.z4-forum.com/forum/viewtopic.php?f=2&t=71816

 

[Beetlegav]

There is no change in performance. Ask anyone that claims there is to try and explain what backpressure is, and how it could ever be useful to have pressure resisting exhaust flow. Then have them explain exhaust scavenging.

Backpressure ALWAYS hurts performance. Scavenging helps performance. Backpressure is a byproduct of scavenging, because a smaller diameter pipe will have increased exhaust velocity but cause more fluid friction (limiting max flow). Cutting off the pipe is like having an infinitely large pipe. The forward sections of the exhaust is where it really matters, especially in the headers. By the time you get to the muffler, all scavenging is done and you can do as you please.

That sounds convincing but it contradicts what our own "Beetlegav" found to be fact :?

http://www.z4-forum.com/forum/viewtopic.php?f=2&t=71816

Should really update on there... Oops.

I found when I put the standard back box back on I lost power further... Now I'm back on the debackbox it increased
My issue is my vanos seals need changing, the vanos system works yes but it's not doing its job properly because the seals are toast!
Also my DISA valve was broken.
I think most people would find when sticking a car of similar age to mine on a rolling road it's probably down on power too.
I've bought the seals I just need to brave taking the valve cover off and removing the vanos system

 

[mr wilks]

That makes more sense Gav . Will you be getting a fresh read out once all work is done ?

 

[Beetlegav]

Yeah more than likely, haven't a clue when though

 

[jevans]

I'm not too concerned about drone as it's not my daily driver. my main concern is dropping performance and one thing to take into account is that a lot of our cars will differ slightly on performance due to their age and maintenance but it does put me off hearing form people that have noticed low end power loss.

 

[pokeybritches]

Power loss from a muffler delete is one of the biggest internet/forum myths. There really is no change in power. The only way you can lose power that far back in the exhaust system is if you add a restriction, either by decreasing the piping diameter or adding extra bends (by the way, in fluid dynamics, each bend can be converted into an "equivalent length" of straight pipe to calculate the total resistance to flow... in many OEM mufflers, the exhaust pipe makes several passes through the box, which is equivalent to having many more feet of pipe sticking out of the back of the car).

Don't get me wrong... I don't support cutting off the muffler as a mod, as I think it cheapens a car. I would pay the money for a real setup. I currently run a full Supersprint setup: headers, s-pipe, y-pipe, muffler. But to each his own, and I know not everyone agrees with paying as much as I did for an exhaust system. A sports car needs sound! If cutting off your muffler is your thing, go for it... you definitely won't lose power.