710n's Fitted, but getting a semi-dump Sound... this normal?

[ZeroK66]

Hi Guys,

Ignoring the fact that my engine is days away from being totally stripped to bits for many exciting thigns to be fitted... recently I have noticed on part throttle driving sometimes I hear a little bit of a whosh noise - VERY quiet, but still noticeable.

I drive everywhere with the windows down, so maybe that is the only reason I hear it. About 3k... part throttle squeeze, then let off and I get a tiny cchhh.

[GrahamS4]

I hope it's normal!

Mostly notice mine in 1st gear, but I quite often hear a tshhhh.

[Russ,greys4]

yeah i think its normal, i changed mine 2 forge ones ages ago allways made a slight tissshhh! noise. got louder since i changed the exhaust!

[Mcdubber1]

I get the same sound since i drilled my airbox and i've still got the standard 710A's. Got 710N's to fit so hopefully it get's a wee bit louder.

[GrahamS4]

Can anyone explain why we hear a noise when they are recirculating DVs?

[h8cak]

It can be herd more when a cone filter is fitted. The S4 isnt too bad but my T Sport sounded like i had a dump valve fitted. It was very loud.

[Dr-Al]

Can anyone explain why we hear a noise when they are recirculating DVs?

.

Here's my theory:

If there is a substantial charge pressure built up when they open, the air from the charge pipe and ICs gets 'recirculated' (ie dumped) into the hose between the Y-Pipe and the turbos.

The charge pipe and ICs contain a substantial volume of air that was under pressure. When this pressure is suddenly released, there is sufficient compressed air released into the open part of the system to allow it to briefly expand up into the Y-pipe and out of the intake.

This is one of the reasons why these cars use a hot film MAF and not a filament. The hot film can measure the direction as well as the amount of air passing over it, so it is not 'confused' by air 'going the wrong way'

[h8cak]

Cheers Doc................. now im even more confused

[ZeroK66]

Cool all is well then - wonder what it will sound like with a set of K04's

[Dr-Al]

Cool all is well then - wonder what it will sound like with a set of K04's

The magnitude of the decompression is proportional to both the volume of the compressed gas and the pressure difference.

IIRC, K04s have a 0.6 Bar wastegate actuator as opposed to the 0.4 Bar actuator on the K03, so this will increase the 'no load' charge pressure (ie the charge pressure with the N75 at 0% duty cycle), so I would expect the dump to be louder with the K04s.

Also, having a larger volume path after the turbos will increase the effect. So having RS4 ICs or a FMIC will also make it sound louder.

[GrahamS4]

Totally different. I couldn't believe how like a totally different engine KayGee's car sounded. I actually prefer the sound of mine. Which is handy.

[Dr-Al]

Totally different. I couldn't believe how like a totally different engine KayGee's car sounded. I actually prefer the sound of mine. Which is handy.

It would be chavtastic to have it as loud as possible!

I don't hear mine at all and that's the way I like it. There are plenty of spotty oiks driving around our town with their cars going Psst! every time they change gear. I don't feel any urge to be associated with them!

[S4TAN]

plenty of spotty oiks

Death to spotty oiks I say!!!!

[david7m]

My 'dumping' seems to get louder when the air filter needs re-oiling. Will be doing this shortly.

Dave

[ZeroK66]

I think the more turbo & gushing noise you hear when thrashing the car the better. BRING ON THE K04's...