Noticed on my 2019 GTC that the exhaust noise does not immediately get louder when the Sport+ Exhaust button is pressed. You need to increase the rpm and then when back to idle the sound is indeed louder; but if you actuate the sport exhaust at idle without revving, the idle sound barely changes. The exception being if you press the button upon a cold start.

Anyone else notice this? Perhaps the more knowledgable members here can explain what is happening. I would have thought the values are either open or closed. It seems like they need higher exhaust pressure to open fully, so once you get the engine speed up, the valves open further and then stay open even at idle, until you close them.

 

Hi Surge,

I might be able to add a little detail.

The exhaust flaps are controlled in the ECU and there is a pretty complex algorithm it uses to manipulate the exhaust valves based on certain design output expectations, some of which are performance related, others are EPA governed.

I've been working a project looking into the data tables partly for curiosity reasons, and partly so I can modify the tables if I choose. The M176, M177, M178 platforms are not easily accessible at the moment, but I can give you some illustrations using some older AMG platforms.

Here is a typical higher (highest) level of data tables for the exhaust valves. Just scanning it you can get the feeling the various operating situations the flaps would be manipulated in the tune by the ECU:



All of these tables contain data related to ECT, ETC (commanded positions), RPMs, and various other data. The ECU scans these tables and chooses valve opening given the present operating conditions that match the table definitions.

When you start to look at the data in the tables, there is a primary table (using a protocol similar to the way most EMSs choose ignition timing). A primary table establishes the opening, then that opening % is adjusted using a "modifier table" based on other criteria. That other criteria could be ECT, RPMs, air density, etc. It is a small look into why you don't tend to see much of a repeated pattern that makes much sense.

In the illustration below, this is a blowout of some of the exhaust flap tables. Lower right is the higher level table, the other individual screens is a selection of those tables. The primary table is the one located in the lower left of the illustration. It is marked "Exh Valve RPM Thresholds". You can see it's "bubble" in the lower right hand table I've circled, it is the fifth bubble from the top. That is the table the ECU goes to first, it establishes a position based on the highest level table conditions that exist, then will adjust the final flap output based on any of the secondary tables that apply. Of course, the first criteria of the primary table is the "mode" commanded by the driver.



Hope this gives some insight.

Best,

 

Hi @Acta_Non_Verba - WOW! So interesting. Amazing that you know so much about this!

I had assumed, wrongly, that the valves are either open or closed; but I now see that's not the case, and there's a range of opening that the ECU can command. Also, looks like there are 3 valves, correct?

On a related note, I had 1 stuck valve (probably when I cold started in -20C weather and immediately pushed the sport exhaust button - one valve was probably frozen). Once the fault was registered, the ECU would no longer try to open that valve, despite repeated pressing of the button. However, when moving the drive mode selector into Sport+ (or presumably Race), then the valve did open. And it has worked fine ever since. This could be useful info if this happens to anyone else.

 

Hi Surge,

Just two valves and yes, varying degrees of open given numerous different inputs.

For 100% open, a device like Renntech's works, I hear. It intervenes on the supply voltage and sends full voltage to the solenoids while still allowing the ECU to think it's controlling the voltage. I'm about ready to purchase one of these, not to try to reverse engineer it, just to understand how their ECO workaround is designed. The built in check diagnostic might be very simple and just checks continuity on a startup, but if there is a continuous verification of the varying supply voltage, that would make the aftermarket devices more complex.

 

Definitely let us know if you purchase the Renntech device. I would be interested in using it to keep the valves fully open all the time.

My service tech, who actually is very good, mentioned there are 3 valves, and I noticed in one of your screenshots above that 3 valves are referenced. See under Active Exhaust...?

 

I just did the Cete on the Pro I got.

It does the same but allows you to work it through the OEM valve button rather than working around it. The downside (that i don't like) is that it doesn't cold start and it doesn't remain persistent with my choice like the Renntech EVM does. Pros and cons for each really, but for me, my OCD wasn't going to tolerate the exhaust button not working.

 

I too noticed that the valves were not simply open or closed. Even in some instances where the valves should have been open, they were definitely not. It was frustrating.
I have the Renntech unit. Set it to open over a year ago and have not messed with it since.
What I did notice in my case is that the car is now louder with the Renntech unit than it ever was prior.

 

Hi,

The GT models have only 2 actuators. (Valves) The 3rd actuator is at least intended as an output on the control unit.
I don't know if there is a control signal there. Don't believe it.

Your service mechanic is not entirely wrong.For example, the C63 has 3 actuators. The 3rd sits in the "H-Pipe".

As far as I know, this is closed when idling, to completely separate the cylinder banks.(Classic V8 double exhaust sound)


Best regards

Stenzel

 

Interesting, thanks. Was the install complicated for the Renntech unit?

 

Yes, this is why when I looked at what was out there I prefer the Renntech - set it and forget it.

It has to be louder overall, as there are so many situations with the factory setup that would only partially open the valves; or, put another way, fewer situations when they are wide open. The Renntech is feeding the solenoids full voltage so can't help but to be wide open.

Also, as sensitive as these valves are to failures (described in many posts), just keeping them in one open position is preferable to them getting fed varying voltages all the active time of operation.

 

Will the Rennteh still close the valves when the engine is not running, or can you force them to stay open?

And can you manually force the valves to open, even if what is stuck and reads a fault? This happened to me in the winter: 1 valve didn’t open. The ECU disabled the exhaust button because of the fault; although it turned out that moving the drive mode selector to Sport + reopened it (I think - I took it the dealer and the tech also cleared the code). But it was interesting that the exhaust button was just disabled by the ECU when it detected a fault. It would be great if the Renntech could override that and trigger the valves to reopen.

 

All,
I don't mean to sound like 'that guy' but does the Renntech EVM do more than merely increase the rumble of the exhaust note?
For $700-720 @ Vivid Racing or $760 thru Renntech, it is a pretty penny for a slight increase in rumble.

Does it increase the sound of pops & crackles? Am I missing something?

How does the Cete work (differently?) & does it sound any different?

 

For the 18 GTR the Renntech module only gives you open cold start and open comfort mode. Maybe a tiny bit louder low end (Placebo effect?)

The Cete I don’t own but from what I gathered it starts in comfort mode with valves closed unless you intervene before starting which is an extra step.

 

Is the Renntech module a difficult install?

On a related note, how do you do the “emotion start”? Never figured that out…

 

If I'm not mistaken, isn't the 'emotional' start only noticeable on the 2020 model year? With my 2018 GTC I've tried starting GT while pulling while both paddle shifters at start-up... no noticeable change in sound. I've also pushed the start button (w/o foot on gas pedal) turning knob to S+ or Race, then starting GT... again, no noticeable change in start-up sound.

Renntech or Cete don't increase 'pops & crackles'... they only make the low rumble at idle more noticeable with the valves fully open all the time?

If someone wants louder 'pops & crackles' then it's suggested one removes the 2nd cat mod.???

Am I wrong with my understanding of the above three (3) assessments?!?

 

Youre kind of right, but not sure you understand it all.

First, valves don't create pops & crackles. Only a tune can change that. And, they are only ever present when the cars are set to Sport + or Race. They aren't there in C, or Sport settings. They're kind of 'racer boy' in the end...its wasted fuel igniting in the exhaust gas, so tunes will add them for fun factor, but they are just that fun - they dont improve performance.

Circa 2019 these cars got a LOT quieter for a couple of reasons - first, they came with the dreaded OPF, which choked out the exhaust gases in an added emissions piece that also quieted the engine a LOT. Second, they further retarded the 'open' setting in the valves further reducing the noise coming from the exhaust. There are really 3 things you can do to change that; the first of which being the least expensive and least invasive option - adding an EVM....either RennTech or Cete. They both cheat the factory system into opening the exhaust valves fully without throwing a code. And, they both get there differently, so its usually personal choice for which one you choose - they are both about the same price. Around $700.00.

The other 2 options get pricier and more invasive. You can tune to get better performance and add more pops and crackle (fun factor). This will set you back around 2500 but wont overcome the muted sound from the OPF filters and you will still want an EVM. Finally, if these two combined arent enough, you can start replacing downpipes but then you open up emissions issues, warranty flagging etc. Some do it, but its not for everyone.

So to recap: quick fix is $700..second stage fix is $2,500 to $3,200 and add downpipes and the stage 2 tune prepare for $5,000 to $7500 plus potential warranty issues.

 

Just wanted to add the quieter cars started with MY2020. MY2019 cars were just as loud as the earlier cars. It started with the interior facelift and other minor changes.

I do love the pops when lifting off the gas with sport exhaust on, it’s noticeable in all drive modes, but not always.

 

I thought some of the Euro 19s had the OPF too - 2020 for sure tho!

For the pops etc, I thought that too, but Stezel pointed out they only happen in Sport +... I was convinced otherwise and I tested it; he was right. They only exist in Sport +...none of the other ranges create that effect, unless you select that setting in your individual option.

 

I do hear some pops on overrun, lift off the gas and you hear them, occasionally. This is with the sport exhaust on and in any drive mode, even comfort.

 

Not even in my Pro will it do that....and I am not gentle .

 

Indeed, I never noticed this in 2 years of driving, but after my tech looked over the exhaust valve that had not opened, it's been doing it ever since. Perhaps a software update? He didn't do anything other than clear the code and perhaps update the software. The valve opened on its own when the drive mode was put in Sport+.
Now when I lift off the throttle, especially under moderate to heavy acceleration, it will burble when the exhaust is in Sport+ and you lift off the gas. Not always and not nearly as loud as when the drive mode is in Sport+, but it's definitely audible.

 

I put a Renntech EVM in my '16 GTS. It was a noticeable difference but not a significant difference. Install was easy except for the damn cover you have to pull off to get to the passenger footwell fusebox. The instructions showed two bolts...there are three. Other than that it was pretty much plug and play. I do like that you can turn it off so my neighbors don't hate me more than they already do. If I had to do it all over again I would have saved the money, gotten rid of the cats, and not be worried about my neighbors.

 

Hi DCBNA,

YES, that passenger's footwell cover is a gem, isn't it!

 

For all of the reasons already shared, this led me to purchase the Renntech unit. It works and is more of an on/off button. Slick remote as well that I leave in the car at all times. Definitely not inexpensive, but it works.

 

I have the cete device and it IS able to perform a cold start. What you need to do is press the power button twice without having your foot on the gas. The first press will power the car on, and the second press will illuminate the driving mode knob. Select sport + and then press the power button a third time with the gas pedal pressed. This will perform the cold start with the valves open and it will sound much louder. I have a 2019 GT for reference.