Scirocco Central

James321 wrote:I'm baffled (pun intended) on these Milltek issues, how can a resonated system, especially the EC approved one cause drone and yet a non resonated system with only an average size middle silencer and nothing but pipe work at the rear not cause any drone.
If this is some sort of resonant frequency caused by the lengths of the pipe inside the silencers then surely Milltek can alter this and cure the issue?
I thought the EC approved system was just that, it met with European noise regulations?

The BCS system is also confusing me, it's the same, an average size centre box with a small straight through silencer forwards of this and yet it's claimed to be quiet?
My Acrapovic system was two rear silencers, one at each side and a straight through silencer to the rear of the down pipe, it still boomed at motorway speed even thought the construction was superb.

The difference with the BCS system is the valve. you should talk to Nige he can give you full info on the engineering.

Well the valve itself doesn't make the difference, from what I can see- with the valve closed the exhaust is routed through the centre box and it's set of baffles, with it open- it takes a more direct route straight through the centre silencer bypassing the internal baffles so in effect it's switching in and out a set of baffles inside the silencer (Nige, please correct me if I'm wrong here).

What is confusing me is why all the systems running a rear box in the standard location produce booming at motorway speed.
Look at eMil-VR6's Eurojet system, it runs 2 centre boxes and a large rear box and yet it still drones.
My Acrapovic, a cat, a front box and a large rear box; The Milltek EC system, 2 centre boxes and two large baffled rear boxes; Milltek resonated, 2 centre and 2 small rear boxes. All those systems have reported as droning/booming on the motorway.
BCS and Milltek non resonated both don't use a rear silencer and yet both are reported to be quiet.

Maybe some dynamat (comes up as dynamite on predictive text) on the boot floor would help to reduce the vibration?
Interestingly, I fitted the Eurojet down pipe to a standard system, there is no booming or drone at all, it is louder on full boost as like the BCS it uses the valve to open up the second tailpipe but unfortunately the sound it makes is like a wet fart on gear change. It has kept the majority of the performance but has taken the edge off it slightly as I believe the rear standard silencer is restrictive.

Your not far off with your analysis James...

blurb... http://www.powervalve.co.uk/powervalve/" onclick="window.open(this.href);return false;

Predominantly It's all about the development and testing - making sure that there is no drone is the (or should be) the number one requirement from a sound point of view of any performance exhaust. However, having the knowledge of how to do things correctly in the first place helps.
I know the exact reason why our system does not drone and in actual fact the reason why the milltek non res doesnt (Although looks like more luck than judgement as why not dial it out on their other system variables).
Additionally why the Akrapovic does - but then again that's what 35 years in this industry gives you,
Cheers
Nige

If anyone wants to see some more video of my BCS system let me know

I can say for sure the Milltek non res cat back system that Was developed on my R, was loud and did drone whilst cruising on boost at certain revs. Off boost it was ok. I was surprised they removed the valve function whilst developing.

It was particularly bad when starting up from cold and the boom upto 2k rpm was just way too much.

I actually enjoyed the car again when the Milltek came off and I refitted the original before selling the car. Was bliss!

I would recommend just fitting a down pipe and leaving the OE cat back system in place.