AFN Cat Trap: Humane Wildlife Control

Hi,

I'm completely new to this forum, and from what I can see, there are people here who really know a lot about diesel engines.

I have a question:

What are the effects of removing the catalytic converter? I know it's illegal, etc. I just want to know how it affects engine performance, smoke emissions, and fuel consumption.

Most of the people I've asked so far say that the engine will become weaker! But I can't believe that. Because there's less back pressure, the engine will become weaker.
It's possible that a naturally aspirated gasoline engine might produce less power at low RPMs (due to insufficient back pressure). However, it should offer more power in the higher RPM range. Otherwise, people wouldn't install performance exhaust manifolds (of course, not on turbocharged engines).

Wouldn't it only be advantageous for a turbo engine if there was less back pressure?

For example, if you consider when manufacturers first started installing catalytic converters, the engine power of vehicles with catalytic converters was often more than 10 horsepower less.

Has anyone ever experienced a catalytic converter failure in a TDI engine?
So, can anyone share their experiences or knowledge?

I am grateful for every contribution!!!

konjoy wrote:

Most of the people I've asked so far say that the engine will become weaker!!! But I can't believe that. Because there is less back pressure, the engine will become weaker.

A defined back pressure is important for every engine. The exhaust and intake systems are designed to accommodate this.

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It's possible that a naturally aspirated gasoline engine might produce less power at low RPMs (due to insufficient back pressure). However, it should offer more power in the higher RPM range. Otherwise, there would be no reason for people to install performance exhaust manifolds (of course, not on turbocharged engines).

"Special exhaust manifolds are also used in turbo engines. However, these engines are usually racing engines that are typically only operated in the higher load range. In the mid-load range, these engines are sluggish and inefficient."
A straight-four engine is always a compromise.

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Wouldn't it only be advantageous for a turbo engine if there was less back pressure?

The back pressure in a turbocharger plays a relatively minor role, so removing the catalytic converter is unlikely to make much (if any) difference. The turbo boost is already limited by the engine control unit (ECU), and the fuel quantity is adjusted accordingly. Without further modifications, nothing will change.
Due to the reduced back pressure, the turbocharger spools up faster, which, in the long run, puts extra strain on the turbocharger's mechanical components.

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For example, if you consider when manufacturers first started installing catalytic converters, the engine power of vehicles with catalytic converters was often more than 10 horsepower less.

It wasn't the catalytic converter (KAT) that was the problem, but the fuel. Super gasoline used to have 98 octane, while the initially offered EuroSuper only had 95. Therefore, the engine designers couldn't use the same ignition timing for maximum power as they could with 98 octane (with 95 octane, the ignition was set to a "later" timing).

Hello,

"By reducing the back pressure, the pressure drop across the turbine increases, allowing it to produce more power. That's the theory. In practice, the expansion of the Kats will only reduce the back pressure by a few millibars, so you won't notice much difference. I don't foresee any increased stress on the turbine's mechanical components, as the turbocharger in a car is designed to constantly spin up and down."
Increased soot formation is also not to be expected, as the soot in the catalytic converter is no longer oxidized anyway, due to the low temperatures.
Conclusion: In my opinion, using a replacement part for a cat tree is only justifiable for cost reasons (because you don't want to buy a new one). Whether or not to do so illegally is a personal decision.

Best regards,
Albrecht.

@ Albrecht: And what about the emission values without a catalytic converter?

Hi Black,

If the emission values without a catalytic converter were sufficient for classifying the level of pollutants, then there would be no need for one, right?

Best regards, Rainer.

Sure,
"However, with the TÜV/AU inspection, only the opacity, i.e., the soot content, is measured. For comfort reasons, specifically due to the smell (e.g., in traffic jams), I would personally only use a genuine catalytic converter."

Hi,

It's not worth enough to ruin a cat over. If it was already broken, that's a different story.

I can't say that it noticeably made a difference.

Regarding the environment, Gustav is naturally right.
I have adjusted the boost pressure so that it doesn't produce visible black smoke when running at full throttle on the highway.

Für die Folgen der 1,2 Bar Ladedruck liegt ein 2. Chargers in stock.

The chip, the EGR valve, and a functioning MAF sensor signal were crucial for the engine's response.

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Sure, it will also exceed the threshold for the boost pressure after a few seconds, reaching its maximum value.

Hi diesel.gustav.
Okay, I've been driving for 60,000 km without a catalytic converter (not "removed," but completely without one), and I haven't noticed any negative side effects. The boost pressure stays well within the factory specifications (AFN). The reason for removing the catalytic converter was primarily practical, because the catalytic converter housing is very difficult to fit in the exhaust system on a T3, and also, the heavy catalytic converter can cause the exhaust system to crack due to vibrations on gravel roads (I've experienced and seen this myself). There are no noticeable positive effects either; whether the catalytic converter is there or not seems to make no difference in practical driving. Of course, the comparison to a standard TDI is a bit misleading, because the exhaust system was never designed like it is now for that engine. It seems to me that the influence of the exhaust system is quite small in a turbo-diesel, and I once had to drive in Iceland without a muffler (it had broken off), and there was nothing noticeable in terms of engine behavior. Even the noise level only increased slightly.By the way, I am not driving illegally without a catalytic converter; I pay taxes based on weight, and the emission class is irrelevant . The engine was also registered without a catalytic converter.

Regards,
Jens.

Hello, I am still interested in the 'Low-Speed Syndrome' described by haehnlein.

/viewtopic.php?t=4711&highlight=flashover

I suspect a connection with the catalytic converter (Kat). Does this effect occur in the vehicles mentioned without a catalytic converter?

... and a happy and healthy New Year '04.

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Unfortunately, I didn't understand your text. I've read it twice, but I still don't know exactly what your response to my post is supposed to mean.

Hi Gustav,

Was a text so complicated? Well, you can always judge your own writing so poorly.
So:
- I drive a 1.9 TDI (AFN) engine without a catalytic converter.
- I can't observe any effects whatsoever (neither positive nor negative).
- I once drove 1000 km without a silencer and didn't notice any change in the engine's performance.

I just wanted to express that the concerns about running a 1.9 TDI engine without a catalytic converter are probably unfounded, meaning I don't see any major problems with driving without one. However, there's also nothing positive about it, so if I had a standard TDI with a catalytic converter, it would still be there.

Regards,
Jens.

Hello,

I need to bring up the topic again .

Is there a ready-made catalytic converter available from a manufacturer specifically for the AFN engine?

I need to remove my catalytic converter because the back pressure in my exhaust system is too high.

Regards,
DJ.

Supersprint and MK manufacture catalytic converter replacements and exhaust pipes.
I've been driving my A3 (engine code: AGR) for 2 years now with a Supersprint catalytic converter replacement.
The engine has been chipped to increase its power to 125 horsepower.
Subjectively, it feels more responsive when accelerating, especially in the higher RPM ranges.
However, the result cannot be directly applied to the AFN, as mine still has a fixed loader.
"Experts" had predicted that the engine would perform worse because it needed back pressure (which is nonsense), and that the turbo would overspin (which also didn't happen).
The exhaust emissions have not increased. The sound has improved .

Yes, the issue with 'lack of water pressure' is probably a widespread myth, as I also had to realize during a conversation with a colleague.

Where the back pressure and the timing of the reflected sound wave definitely have a significant influence, is the slotted two-stroke Otto engine (with reverse scavenging, cross scavenging, star scavenging, etc.).

For any 4-stroke engines with fixed valve timing and a wide operating range (such as automotive engines), the following applies: The lower the back pressure, the better. Lower back pressure directly affects torque, maximum power, and efficiency.

Reasons:

1.) Higher back pressure on the piston during the exhaust stroke results in a lower torque peak (this does not apply to the back pressure caused by the turbocharger, but rather to restrictions such as the catalytic converter).

2.) After the exhaust valve is closed, a residual amount of exhaust gas remains in the combustion chamber, along with a residual pressure. The back pressure in the exhaust system directly influences the residual pressure (and therefore the amount) of the remaining exhaust gas. This can also be described as internal exhaust gas recirculation (EGR), which unfortunately increases rather than decreases with increasing load and engine speed.
The higher the residual pressure of the exhaust gases remaining in the cylinder, the lower the amount of fresh gas that can be drawn into the cylinder, as the residual gases occupy a portion of the intake volume.
A higher (internal) EGR rate, however, in turn (especially at full load), results in a poorer combustion efficiency, meaning potentially more soot due to less oxygenated combustion air.

Conclusion: When testing a street-legal TDI, a noticeable difference should be evident if the turbocharger is failing, especially concerning emissions (compared to the stock exhaust system, particularly if the catalytic converter is already partially clogged).

SeatArosa1.7SDI wrote:

... For any 4-stroke engines with fixed valve timing and a wide operating range (such as automotive engines), the following applies: The lower the back pressure, the better. Lower back pressure directly affects torque, maximum power, and efficiency. ...

If you've ever ridden a four-stroke engine with a carburetor and no exhaust, you'll know what I'm talking about.
Even modern fuel injection engines are quite sensitive in this regard (although less so than carbureted engines).
You can't make such a general statement like that.

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1.) Higher back pressure on the piston during the exhaust stroke results in a lower torque peak (this does not apply to the back pressure caused by the turbocharger, but rather to restrictions such as the catalytic converter). 2.) After the exhaust valve is closed, a residual amount of exhaust gas remains in the combustion chamber, along with a residual pressure.

Have you ever heard of "flushing" a cylinder, and how it's done, and what it's used for?
Apparently not! -> "Ludwig Apfelbeck - Paths to the High-Performance Four-Stroke Engine"
Even he writes about a "defined throttling of the exhaust flow."

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... Conclusion: A street-legal TDI should show a clearly measurable difference when the turbocharger fails, especially concerning exhaust emissions.

(compared to the stock exhaust system, particularly if the catalytic converter is already somewhat clogged). }

Then explain it:
1Z engine with catalytic converter and complete exhaust system -> 94 horsepower.
1Z ohne KAT aber mit restl. Exhaust -> 93 horsepower.
1Z ohne KAT und restl. Exhaust -> 89 horsepower.
1.6L engine with catalytic converter and modified exhaust muffler -> 97 horsepower.
1Z engine, without catalytic converter and with a modified muffler -> 95 horsepower.

"These measurements were taken by a fellow motorsports enthusiast on the same LPS002 device on the same day (with consistent weather conditions). He had actually intended to write a paper about it, but he abandoned the project after this result. The modified muffler was a commercially available, branded sports exhaust system."

If you consider that to be "clearly measurable"... for me, it all falls within the measurement tolerance.

"I agree with you that the influence of exhaust backpressure on turbocharged engines is significantly less dramatic than on naturally aspirated engines. However, this is because most of the backpressure is actually generated by the turbocharger itself."

Have you ever heard of 'flushing' a cylinder, and how it's done, and what it's used for?

Only in the context of two-stroke engines. In four-stroke engines with fixed valve timing and non-overlapping intake and exhaust opening times, a 'scavenging' process in the true sense cannot exist, but only a clearly separated exhaust and intake stroke.

Your 1Z example is not logically explainable. It's either due to measurement errors, or a phenomenon related to the wastegate turbocharger and its control system.

SeatArosa1.7SDI wrote:

... In 4-stroke engines with fixed valve timing and non-overlapping intake and exhaust opening times, a "scavenging" process in the true sense cannot exist, but only a clearly separated exhaust and intake stroke.

Setzen ... SIX

This is almost the same principle as in a two-stroke engine. However, here, it is achieved through the overlap of the valve timings. So, the intake and exhaust ports are simultaneously open. That's precisely why the issue of back pressure is not a myth. You have already explained the rest very well.

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Your 1Z example is not logically explainable.

For me, it already is (see above).