View Full Version : difference db killers euro 3 and euro 4 Akraprovic

03-06-2019, 09:01 AM
Hello, I have the Akraprovic euro 4 silencers but no Shiver 900. The Shiver 900 has been ordered and I'm waiting for it.

I will not drive without DB Killers, this is too hard for my ears. Maybe just like my Shiver 750 with akra euro 3 with db-killers in it was perfect. But with the euro 4 I fear something quieter db-killers that's why I:

Only the db killers can come out of the akra dampers euro 4.
It is still very simple, you have to look carefully where you have to drill a hole through the carbon end cap, where the screw underneath of the db-killer is attached, there has drilled a hole of 5 mm and drilled 1 mm to 13 mm , there the akra cap can be nice to seal just like the euro 3 dampers. This bolt is then very lightly welded next to the head (because the law says (db killer must be welded, one does not say how much and where it should be welded: +), just put some power and weld fractures and the bolt is even still usable .

Now I have that because I did not know 3 db-murderers outside the dimensions of the euro that existed there, because my first suspicion is that euro 3 has more noise and less power loss. Although I still know that the Shiver 750 better hang around 6000 rpm with db killers due to slight counter pressure.

What strikes me now is that

-euro 3 dB killers gives the end pipe a passage of 30.2 mm and 100 mm deep in the silencer (measured with a screw).

and the

-euro 4 db killers gives a double end pipe, largest pipe is 33.9 mm and goes deeper into the silencer. 113.5 mm (less noise)
inner end pipe is 28.4 mm and 0.9 mm thick pipe and is 87 mm long measured from screw.

Now I am still waiting for my Shiver, so I can not do a thorough test, but in theory you would think (without thinking about the length) that the euro would give 4 more, but I wonder how far the gap between the 2 pipes is effective. If you compare it with height, the euro 3 is better because it is shorter. And the inner tube of the euro 4 is 28.4 mm and the euro 3 30.2 mm if you do not consider the gap effective, then euro 3 seems better again.

In any case, I'm waiting for the Shiver now

for photos see link (Dutch forum): https://www.motor-forum.nl/threads/s...425329/page-41
I could not post photos on the forum.

03-07-2019, 08:04 PM
Great info, thanks. Unfortunately, you have to register to see the pictures in full.

The baffle's length will almost certainly be for resonance / tone shaping rather than total volume reduction; the aperture area itself determines how much noise gets out, but also comparatively how much low frequency vs. high frequency (larger holes are more bassy). That said, ultimately, "noise reduction" and "tone shaping" are the same thing in terms of the loudness regulation and the aesthetic sound target that Akra had in mind.

I think the double skinned design is to reduce the "flow noise", that turbulent tinny sound from a flow constriction, again helping the aesthetic target - i.e. it sounds meatier and quieter by reducing high frequencies preferentially. Usually when you make an exhaust quieter, it's the high frequencies that very quickly end up dominating the sound, because you have to make the exit smaller to silence it which in turn means the flow has to speed up through it, creating more turbulence.

So although the outer pipe is larger, the small distance between it and the inner pipe, and hence high skin friction of any flow between them, would mean that "annular" space is not a hugely efficient conductor of noise itself; but it will sort of capture some of the turbulence off the inner pipe and reduce its impact on the overall sound.

Clever stuff.