LZH

I know everyone is aware that the exhaust note on out cars at cold startup is pretty loud...but it seems as though the exhaust note is totally different during those 10 or so seconds while the car is idling high. Almost as if there is a butterfly valve inside the muffler that is open then closes when the idle comes down. When my car is idling high during the cold start period, I can blip the throttle and it sounds TOTALLY different than when I crack the throttle after it's warmed up. Has anyone else noticed this and/or know why this is ??

mellowyellow

Yep, the cold bark on fire-up is excellent. Never really bothered to blip it while it was cold.

jrcart

Yes, and it will allow you to rev it up an additional 1800rpm(approx) too. Once it is warm, if try to give it quick, heavy throttle while in neuteral it falls flat and revs slower.

SMP

In cold start conditions, fuel does not fully evaporate. It is necessary to enrich the mixture, providing more fuel than normal so that even partial fuel vaporization produces an ignitable mixture. In the process, the exhaust note changes. The cold start automatic in fuel injected cars makes it much easier than it used to be with carbureted engines. Too much choke and the spark plugs were wet, which meant taking them out to dry.

LZH

Jim - so CLEARLY something is functioning differently during cold start up...do you know what it is ??? I mean, during cold start at 1000 rpms the exhaust note is amazing. Then when the idle lowers and I use the gas pedal to maintain 1000rpms, the sound is mundane and crappy - SO WHAT GIVES>>?? Sounds to me like the mufflers have a butterfly valve but I've never really looked at them very closely...wonder if there is a air line (vacuum line) going into the muffler??

SMP

Luke, no butterflies in the mufflers. Like I said, the mixture is richer in fuel, which makes the engine a little more responsive. After the cold start automatic switches off, the ECU is back to normal and prohibits the engine being revved freely to protect the automatic transmission. You can fool the ECU though. Once in drive and your in motion, if you quickly put it in neutral and blip the throttle, it revs freely for a couple of seconds.

LZH

Damn - good info Sacha, thanks that makes perfect sense. I've actually done what you said...popping it into N while rolling to a stop and it will easily rev to redline. Sounds damn good too. Thanks again for the info.

jrcart

There has been more than one occasion when I've been at a stoplight and some ricer is reving his Civic to 9000 rpm and I've wanted to just put it in neuteral and rev it up to 7000 to show the kid what a real engine sounds like...but no such luck, big brother at AMG made sure that would not be possible, probably saved them countless transmission and rear-end warranty claims.

sprins

Cold start always makes my day: http://www.youtube.com/watch?v=eA0iWA0Pkw4

jrcart

Beautiful...but you should hear it with longtubes, primary cat delete and aftermarket resonators, neighbors don't like it so much, especially since the echo in the garage further amplifies the sound.

sprins

Please do share with a sound clip/video

sechsgang

ya, if you do the rolling neutral blip, you can get a REALLY loud crack out of the exhaust...like gunshot style. Its scared COUNTLESS people. And ya, thats how a REAL engine sounds...well, I do like my V12s and TT flat 6s too...but I wont be picky

jrcart

Unfortunately I do not have a sound clip of my car on cold start up and my car is kinda sorta outta reach for a couple months.

LZH

LOL, to say the least
I'm sure it'll be breaking records soon enough.

PyroLume

Hey thanks for teaching me this.. the a-hole down the street just sent the cops by my house to complain.

LZH

take a ***** in a bag and leave it on his porch.

jrcart

I'm just getting some Mercedes valvestem caps and new wipers installed, those Mercedes valvestem caps are swwweeeeeeeeet, they have the little star on them and they're chrome, I just had to have them. I might get the windows tinted while I'm at it, not sure if they can get through the roll bar to get to the back window though.

TTAMG

Also remember, there is a whole spark table for "cat light off" that pulls timing during cold start which makes part of the combustion event occur in the exhaust to heat the catalyst up and this completely changes the way the car sounds. The first minute or some when doing emissions testing is always the dirtiest because the cats are still cold.

JDB

Gee Jim,

Maybe you should wait on those valve stem caps.

I hear there are some lightweight carbon fiber valve stem caps due to be released, soon.

JDB

jrcart

What's going on with your "project"?

Jeff M

That's what I was going to say but came too late to the party. I agree obviously, late spark has more of the mixture burning out the exhaust/into the cat warming it up sooner. Though this would make for a brief weak engine power condition from not getting enough of this mixture, bumping up the idle speed helps avoid stalling tendencies (and more hot exaust goes through the cat), though some blipping their throttle have found rpms sag a little low at first then jumps back up. Common with a lot of cars these days, not a big deal and I find its faster off this high idle period then other cars. Seeing how close cats are now to the exhaust manifolds or turbine housing, cats light off so much faster now, cold start emissions have always been the toughest to deal with, direct injection is helping there a lot.

ecampbell

Err Black Series stalling tendencies...I have never seen this. Same question for weak engine power...are you starting the car and driving or waiting for it (and the lubricants) to warm up a bit.

Sincity

Even with the limited bark when warm should do the trick.

Jeff M

Uhh, might need to re-read my post, it was talking cold start tuning challenges and effects in general. Underlying to many engines, noticeable more to some, less to others, and stalling not a condition, just nearby but under control LOL.

Is it a good idea to allow the fast idle, opinions vary, oil is getting pumped up to the extensive valve train in this car faster which is good, but its turning more rpms up there till the oil arrives, hence differences in opinions on this being good. I prefer to let it happen in the BS till the rpms drop on their own, about the same amount of time it takes to turn down the stereo, turn on the radar detector, and fasten seat belts , so not a big delay. Then slip it into gear and drive away easy and slowly for a while. In a perfect world it's best to keep the load and rpms down till the engine warms and has been the talk with engine builders and elsewhere in the past, only now do we see it commonly stated as in our manual telling us no hammering on the engine until the oil temps reach a certain temperature. The manual also states at engine temps below 68°F the engines rpms are restricted in order to protect it from damage, software technology is great, a few older M3s and M5s could have benefted from those programming smarts.

TTAMG

Just real busy with work these days. I've been lurking around though. Still doing it but taking my time. You'll see something soon...