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AS mad science: understanding burble. Place for discussion and amateur science.

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On 5/20/2021 at 3:27 PM, HMC said:

It’s more induction rather than exhaust but I will have to dig out a CAR article by LJKS where he discusses with a Honda engineer about induction  harmonics of variable length intake manifolds and the notes on a clarinet

Sports air filters do sod all to performance but what they do do really well is affect the intake noise.

It can transform the feel of the car far more than any actual power gains would, perhaps. 

Modern cars with 'sports' settings mostly just give you more canned engine noise, same effect on the ignorant driver but that's totally cheating. 

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  • 2 months later...

I'm quite curious to get some set rpm samples from the W123.  Unlike the van where the exhaust just sort of did whatever it did, the system on this has clearly been more more thought out.

Manifold has cylinders 1/4 and 2/3 paired, and they don't merge into a single pipe until a good three or four feet along the system. 


Thought I had a photo of the spare manifold off the car, but apparently not.

This car has a VERY pronounced difference in the exhaust note depending where in the rev band you are.  It's very muted at the bottom end but has a really hard edged growl to it that comes in just under 4000 rpm, so I suspect there are some very distinct resonance effects going on there.

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8 hours ago, Asimo said:

Growl maybe intake noise, when 2nd choke opens?

Not in this case as it's injected.

Just made a point of snapping a couple of photos of the spare manifold.




It's actually in the first exhaust box that the two separate branches merge.

The downpipes themselves are missing in this image.


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I'll at some point be able to offer recordings of:

- Volvo (Audi/VW actually) 2.5 TDI

- Peugeot 1.8 XUD

- Ford 1.4 Zetec (I think)

- Citroen 1.6 TU in 16v 110hp flavour


Unfortunately half of them aren't running right now, well maybe even 3/4 if the battery on the fiesta is dead. By the time it's running the XUD may have a cherry bomb on it as the original back box has a big hole in it, but that just adds more flavour to the sound surely? :D


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