[Frederik1111]

Hi,

I've lately been looking at some opportunities in regards to changing the exhaust note a bit on my 2007 N52 powered 325i E91. In Europe where I'm local, there are not so many exhaust options, and most of them are pretty pricey. Finding a rear muffler is rare for less than 500$.

This is the sound I am going for:

So I was thinking, could a modification to the front collector pipe affect the sound because one pipe becomes different in length? The modification would be after the primary cats and before the secondary cats

For reference, this is the Laptorr exhaust system - notice the 'twisted' pipe that looks to be achieved with a 180 degree bend right before the resonater:




Now, this is the undercarriage of an E90, as you can see the two connecting pipes are roughly the same length. I think if one of them is made longer or shorter by a considerable amount, the 'laptorr effect' will appear. I marked a suggested change with blue lines.
In essense the principle is the same as that of Subarus with unequal length headers, since the exhaust pulses will be timed differently by changing the length of the pipes before they are merged (which happens in the resonator on the N52).



Now obviously it will be necessary to get out to the car and measure to be sure of what possibilities there are. Also the bracket needs to be considered if doing this. Practically I think this could be done with a short 45 degree bend and a straight pipe in between, either welded or clamped together.

Do you think this could change the sound? Would you consider doing this modification to find out?

My primary issue that I haven't got the skills, a welder or a shop to carry out the idea, however if I become more sure that it will work, it might be possible to get a 3rd party shop to do the mod.

This is the entire N52 exhaust system diagram, for my idea, the change will be made in the area surrounded by the red square, just for clarification:

[E92William]

I think it would certainly change the sound quite a bit. The laptorr exhaust kinda sounds like a milder unequal length headers setup. That's kind of what it seems they did there. I remeber honda guys would put unequal length headers on their cars and they would sound a lot better. Unless there's some seriously weird stuff going on inside the muffler (which with the price, nobody is gonna cut open to see) this is the best bet to try and modify.

[b1aze]

So based on the video title, they’ve also done headers which will really change the sound, more so than 1-2” difference in exhaust tube length IMO.

[craz azn]

You’re on the right track regarding exhaust lengths. Some things to keep in mind would be to do whatever changes as close up to the motor as you can, as that will affect the sound the most. Doing changes further back in the system will render them to be less effective.

As referenced to above, headers will single handedly make the most difference in sound. Unfortunately, there is no off the shelf equal length header for these cars on the market... it comes down to space/packaging and also cost of manufacture, but realistically, the 4-5-6 set of any header system needs to be made longer to match the full length of the 1-2-3 set. I imagine the laptorr system adds in a length similar to what’s missing on a stock 4-5-6 manifold in order for the system to act as an equal length setup.

I plan to put this theory to the test in the spring, to cobble together a home-made equal length header setup with my 325i.

[Phil325i]

Originally Posted by craz azn

Unfortunately, there is no off the shelf equal length header for these cars on the market.

True, if you're in a country that drives on the right. But if your car is left-hand drive...

https://www.supersprint.com/ww-en/bm...verter.aspx#!/

[E92William]

My headers look fairly equal

[craz azn]

Originally Posted by Phil325i

True, if you're in a country that drives on the right. But if your car is left-hand drive...

https://www.supersprint.com/ww-en/bm...verter.aspx#!/

The 4-5-6 runners still look short to match the 1-2-3 set. That is a really nicely made header set though!

Originally Posted by E92William

My headers look fairly equal

Equal length generally means from the flange of the head, to the flange of the downpipe.

[Phil325i]

Originally Posted by craz azn

The 4-5-6 runners still look short to match the 1-2-3 set.

Maybe...but I'd trust Supersprint to get the length right.

[craz azn]

Originally Posted by Phil325i

Maybe...but I'd trust Supersprint to get the length right.

Its funny, I actually didn't even pay attention to the whole header itself at first, just was looking at the primary runner lengths ... look where the collectors are. They are the same as any generic AA, Roundelwerk, ebay/knockoff header where the length from the collector to the downpipe flange is majorly different. This makes it clearly unequal length.

[Phil325i]

Originally Posted by craz azn

look where the collectors are. the length from the collector to the downpipe flange is majorly different.

Agreed. But visually it looks like the length of the pipes for each 'bank' (cyl 1-3 and 4-6) are the same.

[Rebellato]

You can measure by pouring water inside of them and compare the volumes..