Exhaust flaps don't work like the internet would make you be

[DeanoC]

So I've done a few thousand miles with the vacuum plugged and you get what you expect.

Before doing it i read the same thing over and over that in comfort they are shut all the time and in dynamic they open at idle, shut above 1000 rpm and open again at 4000rpm in neutral, 1st, 2nd and 3rd with them being open all the time in 4th - 7th.

That is just totally wrong.

I logged the data in VCDS (rpm, gear, time, throttle position and 245, 246 and 247 for flap signal and L/R position). Looking at it in real time it was clear it is much more complicated and is based on rpm, load, gear and speed.

For example they do open in comfort on WOT, they close almost instantly on deceleration (explains all the extra pops and bangs you get when you disconnect them), they seem to open at 75mph with a low load, i made them stay open at all rpms in neutral by revving slowly, they are closed a lot in 4th - 7th at crusing speeds.

When i have more time i will try and figure it out properly unless anyone knows the answer.

Most importantly it is clearly apparent that the valves have an impact on low down torque and economy. I got 3mpg better on the same driving with them doing their thing. This must be to the low pressure in certain circumstances messing up the scavenging.

[Madelvic]

Fascinating. I've not had my car for long, but I'm bemused about when the exhaust flaps are open or not.

Also, my car seems to forget some of the settings in the Individual mode. For example it forgets the exhaust is in sports mode until I reselect Individual

Don,t know if this is a bug with my car alone

[moonigan]

Fascinating. I've not had my car for long, but I'm bemused about when the exhaust flaps are open or not.

Also, my car seems to forget some of the settings in the Individual mode. For example it forgets the exhaust is in sports mode until I reselect Individual

Don,t know if this is a bug with my car alone

I used to think this and was getting frustrated at having to press the individual button all the time but I found putting the car into S and then back into D appears to wake it up.

P

[DeanoC]

I've noticed that. It's where the D vs S controls things in addition to all of the above and drive select setting.

So you car will start in D no matter what. Rev above 1k rpm when it is cold so the valves seem to shut and then it drops and they stay shut. Once you switch it it stays. Say you have individual exhaust set to dynmic then D and S act the same other than when it starts. All a bit weird

[Madelvic]

Fascinating. I've not had my car for long, but I'm bemused about when the exhaust flaps are open or not.

Also, my car seems to forget some of the settings in the Individual mode. For example it forgets the exhaust is in sports mode until I reselect Individual

Don,t know if this is a bug with my car alone

I used to think this and was getting frustrated at having to press the individual button all the time but I found putting the car into S and then back into D appears to wake it up.

P

I'll give that a go - thanks!

[Geoff A]

Fascinating. i've plugged them under the boot floor, and the increase in noise is very modest, almost bugger all really. And I can't say I've noticed a drop in mpg as a result of this.

[DeanoC]

The only really noticeable difference is on the overrun when you let off the gas. It burbles and pops a lot more.

The other obvious change is a drone at 50-60mph in 7th.

The change in low down torque is noticeable when you plug them back in.

It has highlighted how sensitive these are to back pressure and flow considering the flap is a couple of inches from the end of the system. Messing with stuff upstream must make much bigger impacts

[DeanoC]

Ok i know how they work now. It took 50 miles!

Some important discoveries:

Dynamic drive select or dynamic engine sound has the flaps open 100% of the time. Speed, revs, load are all irrelevant. Exactly the same as unplugging them. It never once shut them even on 40mph in 7th.

Comfort and auto are exactly the same and work on this principle:

Gears 1-4 they open at 3500rpm and close on deceleration at 3000rpm

Gears 5 and 6th open at 3000 rpm and close on deceleration at 2800 rpm

7th works slightly differently as it opens slighlty sooner than 3000 as you reach 80mph but closes again on deceleration at 2800rpm

As for the gear stick. S = dynamic engine map and exhaust sound regardless of drive select setting.

I also figured out the weird starting.

On a cold start in dynamic they will start open and stay open. On a warm start in dynamic they will start shut and assume the comfort/auto operation explained above until you cycle the modes or put it in S.

So basically it is a total waste of time unplugging the flaps as you can get the desired effect in dynamic or in individual or by selecting S. You just lose the option of having it quiet at the flick of a switch with increased torque and better fuel consumption.

[Geoff A]

Top work Deano - I'll go and plug 'em back in then! So getting a bit more sound quality is likely to be complicated?

[DeanoC]

Thanks mate. I really want a bit more noise and have been speaking to a fair few people about it who do this stuff for a living.

There is no quick fix though. It's either buy an off the shelf exhaust (HMS seems the best laid out in my opinion), go custom or modify the standard one.

I will end up with a revised layout upstream i think. First i need to get a used standard one to hack up the mid silencer to see if has a crossover of any sort.

[MikeFish]

Thanks mate. I really want a bit more noise and have been speaking to a fair few people about it who do this stuff for a living.

There is no quick fix though. It's either buy an off the shelf exhaust (HMS seems the best laid out in my opinion), go custom or modify the standard one.

I will end up with a revised layout upstream i think. First i need to get a used standard one to hack up the mid silencer to see if has a crossover of any sort.

Neither the B7 RS4 or C7 RS6 have a crossover in their centre resonators. Therefore I'd be surprised if the B8 did.

[DeanoC]

Thanks mate. I really want a bit more noise and have been speaking to a fair few people about it who do this stuff for a living.

There is no quick fix though. It's either buy an off the shelf exhaust (HMS seems the best laid out in my opinion), go custom or modify the standard one.

I will end up with a revised layout upstream i think. First i need to get a used standard one to hack up the mid silencer to see if has a crossover of any sort.

Neither the B7 RS4 or C7 RS6 have a crossover in their centre resonators. Therefore I'd be surprised if the B8 did.

Thanks Mike. I'd be suprised too. I assume they designed it to do the scavenging at the manifold bank by bank. If so you could potentially get some decent enough gains from an x pipe where the initial resonators are.

[DeanoC]

As a further update i figured it will start with the flaps open on a cold start but start with them shut no matter what settings you have if it's a warm start

[carsarecool]

Ignore all of this and get a Milltek/Akro/Caprista et al.....then you'll really hear the car as it should have been from the factory (obviously in various guises depending which one you have)

I thought standard sports exhaust was enough...until I tried the alternative.

I may be getting another RS4 and the first thing will be an exhaust.

[DeanoC]

HMS is top of my list so far. No way a milltek and the akro is expensive when you could create the same sort of effect for 1/4 of the outlay. + i don't like the tips