Fachartikel über Auspuff-Tuning? | Posts 32+

donalexo wrote:

I definitely think it's possible that the timing of the valve lift in a TDI engine is set in such a way that, with too low exhaust backpressure (no catalytic converter, no MSD/ESD), it could lead to increased scavenging losses. However, this would necessarily require a certain amount of valve overlap (can anyone check this?).

Subject to further review:

Based on my recollection of the AFN engine and the PDE experiments at the ASZ, I am quite certain that when the valve cover is removed and the engine is revved, multiple valves are always open, and that both valves in a cylinder also exhibit overlap.

Without any overlap, all the valves must be closed at every top dead center position, and this unusual sight during the revving of the TDIs would have undoubtedly remained in my memory as a peculiarity.

In older DIY repair manuals, you could still find information about valve timing.
For the R5, overlap was also specified for the 1.4-liter turbo engine (108 hp), but the overlap values were shorter than those for the naturally aspirated engines.

Without any overlap, one would probably only achieve extremely slow running engines, even with forced induction, if the power characteristic still contains some willingness to rev...

Whoever next manages to spin up a TDI without a valve cover or has the timing specifications ready is, of course, welcome to disagree with me .

Quote:

Regarding the turbocharger, it actually always benefits in two ways from a reduced back pressure in the exhaust system: the power output on the turbine side increases, and the temperature level decreases.

If the power output actually increased, then, in my opinion, the boost pressure would also (increase too) much.
I agree with you that a higher potential regarding charging and drive performance is a good thing.

Lowering exhaust gas temperatures is generally a good thing, but it's not necessary for standard production engines.
It seems somewhat uncertain to me whether a potential engine failure due to excessively high exhaust gas temperatures (e.g., caused by 10c or box tuning) can be averted by reducing back pressure. First, one would need to know by how much the exhaust gas temperature (EGT) at the turbine inlet can actually be reduced through exhaust modifications.

Julian wrote:

eike wrote: Wozu dann das Teil? For 3 dB less? Hehe, apparently you generally have bad hearing... I once reversed my ALh and ended up hitting a gatepost with the catalytic converter, creating a €2 hole in the panel. The engine sound was noticeably louder...

My old 1Z engine wasn't quieter with the MSD and ESD compared to running without them. I drove it for well over 100km because the pipe in front of the MSD had broken off. Besides some initial rattling due to the broken pipe, there was nothing noticeable. Perhaps it's dependent on the engine type, as mine was also a 1Z, like eike's.

For example, the catalytic converter (IMO) likely creates a significant amount of back pressure, plus the pressure required to drive the turbocharger - this should actually significantly slow down the engine.
Why don't TDIs without a catalytic converter (still) perform (noticeably) better?


'On my old Ibiza 1Z, the exhaust pipe broke off right behind the turbo. The roadside assistance service told me that I should get it repaired soon, because the turbocharger won't have the proper back pressure due to the exhaust leak, which can cause extremely high and damaging engine speeds.'

Besides the terrible noise and startled pedestrians on the sidewalk (Vienna *g*), I haven't noticed anything positive (in terms of performance).

Yankee wrote:

On my old Ibiza 1Z, the exhaust pipe broke off right behind the turbo, and the roadside assistance service told me that I should get it repaired soon, because the turbocharger won't have the proper back pressure due to the exhaust leak, and this can cause extremely high and damaging engine speeds...

Nonsense, thanks to pressure regulation. But if many brand workshops don't even know about TDI, what can we expect from general repair services...?

Quote:

Besides the terrible whistling and startled pedestrians on the street (Vienna *g*), I haven't noticed anything positive (in terms of performance).

So, that makes it 3 to 1 in favor of increased performance without an exhaust system, if I've counted correctly...

ulf wrote:

Even though the outlet of the exhaust system on Jockel is smaller than the stock exhaust pipe, we even have proof here that the pipe's cross-section is not completely irrelevant: Jockel wrote: In the 1.6-liter turbocharger (TD, JR), the boost pressure increased from 1.3 to 1.6 bar after being modified with a 60mm exhaust (standard 50mm) while the wastegate was blocked, without any further modifications. Therefore, the lower pressure behind the turbocharger already made a difference in that specific case. Well, but with a blocked wastegate, the boost pressure will no longer be regulated.

Hi Ulf,

I didn't write anything about the outlet being smaller than the standard pipe.

The car mentioned above already had a blocked wastegate before the exhaust modification.
The fuel flow was not increased before the test drive with the new exhaust system.
I also assume that the boost pressure enrichment already starts at 1.3 bar.
Maximum amount.
In that case, I don't believe the increase was due to more fuel being used.

Regarding the sound:
With its large exhaust and small sports muffler, it's only slightly...
It got louder, and apparently most of the noise comes from the turbo.

Hi, Jockel.

Jockel wrote:

I haven't written anything about the outlet being smaller than the standard pipe size.

Not written, therefore also my "if" .

But do you still remember the proportions?

Quote:

The aforementioned car already had a blocked wastegate before the exhaust modification. The fuel flow was not increased before the test drive with the new exhaust system. I also assume that the boost pressure enrichment already starts at 1.3 bar. Maximum amount. In that case, I don't believe the increase was due to more fuel.

If the performance has not improved, then that is likely correct.
If that were the case, I think he probably got more diesel - because only a higher boost pressure will reduce performance in case of doubt.

Quote:

With the large exhaust and a small sports muffler, it has only become slightly louder, and apparently, the turbo absorbs most of the noise.

Thank you for the further confirmation .

As a summary of this thread, a first draft of the academic article is now available online.
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

Thank you for all the previous contributions .

Anyone who still wants to contribute can, of course, continue to do so – preferably here.

'Hmm, on our old car (may it rest in peace *g*), the rear silencer rusted off from the intermediate silencer. You could hear it. It was a deep rumble, not loud, but you could tell something wasn't right.'

Best regards, WarLord.

My experiences with exhaust systems with negligible back pressure at VTG:

The turbocharger spools up very well and builds boost quickly. However, this is only relevant up to the point where the VTG (Variable Turbine Geometry) regulates the boost pressure. After that, there are no more differences, which is reflected in the acceleration.

The sound of the exhaust is probably a matter of personal taste. Some people like the rumbling and roaring sound, while others prefer the metallic whistling of the turbocharger. I belong to the latter group.

However, a problem with 'lightweight' exhaust systems is the 'catching' (regulating) of extreme pressure fluctuations for the relatively slow-responding variable geometry turbo (VGT) systems. The turbocharger shaft, especially in vehicles with boosted pressure, quickly enters the red zone. In the long run, this will lead to turbocharger damage. Over-revved compressor wheels 'grow' and hit the compressor housing, resulting in the destruction of the compressor wheel. Bearing failures due to a torn lubricating film are also conceivable, but unlikely. Before that, the compressor wheel would already have 'grown.'


Best regards!

[Translating...]

Hello.

Interesting topic. Turbocharger impeller sizes don't "grow." Furthermore, the back pressure after the turbocharger is extremely important. It must be matched to the exhaust back pressure before the turbocharger, as well as to the flow rate of the turbocharger.


Best regards, Cosi.

Interesting topic. Ladder rungs do not 'grow.'

If they're made of aluminum already...

It also happens with electric motors if they are over-revved.
It's pushing the aluminum out of the sheet metal package. It ends up being quite funny.

CU Gremlin.

Hello.

The consistency of the compressor paste doesn't change significantly enough to be a determining factor for the clearance. If you need a measurement for that, I can try to find it. But you can trust me that it's not relevant.

Best regards, Cosi.

I had my catalytic converter replaced with a Supersprint downpipe.

During the initial test drive, it immediately became clear that the engine provided a very pleasant and rapid acceleration from low RPMs.
That wasn't the case anymore (i.e., after the chip tuning).
There was absolutely no power in the lower RPM range, and from 2000 RPM onwards, it started pushing me back into the seat.
It was very difficult to drive with a child in the car, or with the mother in the back seat.

Now, the power delivery can be much better controlled, and it also feels comfortable at lower RPMs.

The engine responds much more spontaneously in all conditions and feels more responsive when you press the accelerator.

I can't say anything about the top speed yet, as I'm still having problems with the air filter/LLM.
I don't think there will be any changes compared to the standard configuration.

In the coming weeks, I will be replacing the stock muffler with an aftermarket one.
Let's see if there's a noticeable difference this time.
I will also take it back to the testing facility and have them perform another measurement.

I would also find it interesting to know whether such changes affect fuel consumption.
Since I travel to Berlin/Bonn relatively frequently and know my fuel consumption, I'm going to make a comparison in that regard.

My VR6 engine, without a catalytic converter, consumed almost a liter less fuel compared to the standard version.
However, I couldn't detect any noticeable improvement in performance.



Regarding the sound:

When stationary, the overall sound is quite different from when in motion; the low frequencies are almost completely absent, and you can only hear a raspy hiss overlaid with a metallic undertone.
Other people didn't notice it, but I have to say that I have a trained ear and I pay attention to these kinds of things professionally.

The loader is particularly noisy when it's cold. Starting around 2000 RPM, the steady roaring sound immediately changes to a turbine-like noise, which then becomes very quiet shortly thereafter.
Around 2800 RPM, when accelerating fully, a loud whooshing noise can be heard from the rear, which is similar to the sound of vehicles that have been retrofitted with a turbocharger and have a very high power output.
However, this is only noticeable in the first three gears; afterwards, the noise disappears in the wind.

During highway driving, there is only a very slight difference compared to the standard version, which most people will not notice.

There is no sound of burning, but that was to be expected in a vehicle with a turbocharger.
'Of course, there are also turbo engines where you can still hear a combustion noise, but as far as I know, this is achieved either through a bypass or through special turbochargers (for gasoline engines).'




Can anyone here provide information on whether the behavior of the Russian (presumably referring to a vehicle or engine) changes with a modified exhaust system?