asinow

When I fire up my beast, I get a great exhaust grumble that tames in 10 to 12 seconds to a softer pitch. It almost sounds like there's a switch that throws and damper to make it quieter.




Has anyone else noticed this and if so has anyone located this damper or whatever it is so I can keep my initial startup sound? I like my tips and really don't want to replace the mufflers if I don't have to.





















Thanks for any input

JCtx

I asked what it is, but nobody seems to know. My M3 V8 used to do the same extra noise at start-up. I'm pretty sure it's to 'light up' the cats, but have no idea what the heck it is. Seems like an exhaust flap somewhere, like you said. Intake doesn't sound that loud at low rpm and throttle opening. Has to be exhaust related. Maybe the car still has the exhaust ports that used to be required for carbureted cars/motorcycles (bikes still do), to ignite unburned fuel. And there's a valve somewhere. Will remove the engine cover and take a look one of these days, but with everything so tight, doubt will see anything. Having said that, I wouldn't want that freaking noise all the time, but that's just me. Doesn't sound nice; just loud. And coming from the front, sounds like an exhaust leak IMO. By the way, I'm also leaving things alone. Will just change the tips for 2016 ones, and call it a day.

DrRick

It's called 'cold start'. The engine runs richer to heat up the cats as quickly as possible. That's why the cars sound different for a few seconds and then normalize. And our M4 sounds like a complete POS every morning. I've heard chainsaws that sound more exotic...

Dbcooper13

I know I sound like a broken record on this, but cut off your resonators. It only cost $100 and makes the car sound so good...especially the start up grumble.
It's nothing exotic and you don't even hear it under tame driving situations, but I feel like most people here on this forum would love the sound.

johnnyreb

Didn't you Post a Sound Clip of the Difference somewhere on here Db? I do remember you mentioning this on here before though.

Dbcooper13

Both videos suck but here you go.

mjeds

your video is marked as private. can't video it

JCtx

Indeed. But that's NOT the cause of the extra noise. Most cars don't do it, and have to run equally rich. Something else is causing it. Only very few cars make that noise. In my case, just the M3 and the RC-F.

Hey, who was driving that car? Did you see the line of bikers and cars he was holding back? Ha ha. Not being able to leave in the dust a cruiser bike is embarrassing. Ha ha. Just kidding, but it was a waste to be in that car at that place and drive it like driving Miss Daisy.

Joe Z

iTrader: (10)

It doesn't make the noise when the engine is warm..!!!

Nothing else is causing it..

Some of us have been driving these engines since 2008.. Nothing Magical..

The Idle Speed is raised at the COLD START...

If you want the noise to happen when the car is warm.. After you start the car, hold the gas pedal down a few hunderd RPMs.. Noise will be the same

~ Joe Z

JCtx

I know man. But it's not due to being cold either, like you said. It happens when it's cold, but not because the engine is cold. Again, most other cars DO NOT make that noise and are cold too. When the noise stops, the rpm stay EXACTLY the same. I'm a mechanical engineer and don't know what causes it, so no shame in admitting you don't either. Both know it's on a cold start, and due to emissions. That's it. But as a typical engineer, I want to know WHAT causes the sound.. Finally, I'm sure it's already clear to the OP you can't have that sound all the time... nor should anybody want to since it sounds like an exhaust leak. Take care.

Joe Z

iTrader: (10)

Negative..

On an overnight start.. 60 degrees..

My RPMs start off at 1,400 then stages down to 1,200... Then 1,000 ...
Eventually 700 where it all quites down..

The colder outside the longer the process.

It's the increase Idle Speed ...

Here is an example of the Raised RPM's on an overnight first start.


Joe Z

JCtx

My car starts at 1,500 rpm, 'grumbles' for about 5 seconds, then quiets down. But rpm remain at that same 1,500 level for about 5 seconds more. Then gradually starts going down, to around 1,100 rpm, where it stays for a couple of minutes. Then it goes down to regular idle speed of 700 or so. I stress all my previous and present cars never made that sound except the M3 and the RC-F. And my brother's V8 Ferraris (F430 Spider and California) make it too. I'm thinking cars with low fuel economy maybe need a different emisisons system, like the exhaust ports I mentioned before. The M3's V8 had an air pump somewhere (listed in the service manual), and I bet it's related to that noise. It has to be plumbed to the exhaust somehow, and there may lie the enigma.

4everkidd

iTrader: (2)

They must just be giving away those rings these days

Joe Z is correct for both the ISF and RCF. Cold start=higher rpm