Piston Slap: High-Pressure vs. Bore Diameter

Hi, I actually browse through various topics regularly here.
I don't think I've found anything about this before.

It has been described, among other things by Ulf, that a larger hole diameter in the fuel injectors leads to more power. However, there was never any mention of a tendency for misfires.
In comparison, increasing the size of the pump piston from approximately 10 to 11mm also increases performance, although this can lead to jerky operation.
However, there is a lack of practical experience and data to support this point, meaning it is based on assumptions that are theoretically sound.

In both versions, the STG believes it is promoting the original amount.
My question about this is:
Why would the version with the plunger pump exhibit a tendency for jerking, while larger injectors would not? In both versions, the percentage increase in diesel fuel delivery, relative to the original specified values, occurs across the entire speed range.

I'm stuck on this decision and need to choose between the two options in the spring, but I think the one with the piston pump would be better because of the improved atomization.

Best regards,
Peter.

Hello,

Quote:

In both versions, the STG believes it is promoting the original amount. My question about this is: Why should the version with the plunger pump exhibit a tendency for jolting, while larger injectors should not? In both versions, there is a percentage increase in diesel fuel delivery across the entire speed range, relative to the originally intended values.

In both cases, the actual amount of fuel injected is almost entirely dependent on chance, resulting in a discrepancy between the intended injection amount dictated by the engine control unit and the actual injection amount.
Therefore, it's best to have someone do this who is experienced in a) properly adjusting the fuel injection pump, b) correctly setting the fuel injectors, and c) making the necessary adjustments to the engine control unit software to match.

In all the cases I'm familiar with where vehicles were experiencing problems, the issue stemmed from the vehicle owner and their ideas about how their car should be modified. This is aside from problems like defective dual-mass flywheels, pumps containing debris, and similar issues. Self-proclaimed "master tuners" who are only after a quick profit often contribute to these problems.

I don't understand why so many people come up with extremely naive tuning ideas without even having the slightest understanding of what happens and what needs to be adjusted with each modification. They get some tuning nozzles from a friend or buy them from questionable suppliers, screw them in, and that's it. Most of the time, the people who contact me don't even know exactly what was installed, but they expect me to guess it or blindly trust statements like "my friend said they are xxx nozzles and it should all be fine." If everything is supposed to be fine, why isn't it working?

"They're installing used fuel injectors without even checking their proper function. It's a complete joke. Problems are practically guaranteed. Why not just flip a coin? If it's a 6, you get more power; if it's a 1, the engine is toast. It's unbelievable how naive most people are when they contact me with their requests."

The fact is:
- If the vehicle was in good condition and running smoothly before the tuning, it should still do so after the modifications. If not, contact the tuner who performed the work, and do not contact me via private message, email, or phone. And no, I will not take on any projects that are already underway with unknown parts or issues.
- Pump components and nozzles can be used absolutely smoothly if done correctly.

Basically, it's all common sense.

Best regards, Rainer.

Hi Rainer!

Your post comes across as very frustrated. Unfortunately, there's nothing we can do about the fact that you...
I earn money, among other things, by modifying cars, and I focus on...
'People who are quick to offer unsolicited advice or help to others, especially when it comes to their cars, can be annoying.'

I'm already aware that even someone with limited knowledge can navigate the world of TDI.
I tend to move things around and, therefore, experiment more or less. But I also anticipate that...
Problems may arise, and I will personally take care of them.

if the vehicle was in good condition and running smoothly before the tuning, then
Should it still do that after the tuning modifications ?
I also share that opinion, which is why I make sure to find out beforehand, for example, here. I didn't know that you could...
'I've already gotten a lecture about that. I haven't even touched any tools yet, and then...'
That's something else.

My post was actually a request for a comparison between the 'perceived' and...
'described by Ulf, a non-negative critique of jet tuning, and a modification of...'
Piston pumps. As mentioned before, the experimental factor comes into play here, as not all...
Certain details cannot be predicted with 100% accuracy (such as the exact new injection amount).
But wasn't your motto once 'Diesel and enough air - the rest is up to the engine'?
'Physics'.
Is it really so wrong for him to have a hobby in this area, and to occasionally try out the theory in practice?

Are you upset about the customers you've lost? I think you still have enough to keep you busy, right?

PS:
When it comes to DIY projects for personal use, acquiring the right tools is essential.
When it's not worth the effort or cost to do something myself, I also turn to professionals, like the nozzles I purchased from you.
I ordered...

I'll try to approach it with a different perspective.
When performing injector tuning, the injectors are typically adjusted on a test bench. At least, that's how the professionals do it. This eliminates the possibility of misfires caused by inconsistent injection timing or leaking injectors.
However, if only the high-pressure component is replaced, very few people will bother to adjust the nozzles specifically for that reason.
Furthermore, the faster pressure build-up would exacerbate the disadvantages of nozzles with different opening pressures, which would then manifest as jerky movements.

neubaupe wrote:

Why would the version with the plunger pump exhibit a tendency to jerk, but not with larger injectors? In both versions, there is a percentage increase in diesel fuel delivery across the entire speed range, relative to the intended original values.

IMO, the incorrect assumption lies in the bold passage:
The discrepancy between the pump's flow rate and the injection volume generally increases with the amount and speed, because "the nozzle holes are too small at the top end."

If the holes are enlarged, the actual injection amount increases primarily at the top end, while the low-rpm range, which is prone to instability, remains relatively unchanged.

A larger piston might, based on intuition, cause a higher excess flow at lower engine speeds rather than at higher speeds, which, in my opinion, would increase the tendency for jerking more significantly than the maximum pressure (Pmax).

Hi neubaupe,

Quote:

If that's the case, please contact the respective tuner directly and do not contact me via private message/email/phone. And no, I will not complete any projects that have already started with unknown parts/issues.

That's the problem, and I have every reason to be frustrated when at least one person every day wastes my time with it.
"Dummfrech" is the perfect expression for most requests of this kind. I would gladly publish some recordings related to this.

Quote:

Actually, it's all quite obvious.

You seem to understand what I mean, and you've correctly identified the basic principles. Unfortunately, that's the exception rather than the rule. I don't understand how people can tinker with things they don't understand (like fuel injection pumps or MSTGs). And even less, I understand why my number is being called.

Best regards, Rainer.

A larger pump piston, on the other hand (just my gut feeling icon_rolleyes.gif), would likely produce more excess volume at lower speeds than at higher speeds, which, in my opinion, would increase the tendency for jerking more significantly than the maximum pressure (Pmax).

Thank you, Ulf.
Your gut feelings and initial thoughts are always so well-articulated and easy to understand. I feel like we're on the same wavelength in that area.

As an absolute novice in hydrodynamics, I didn't realize that the excess diesel fuel from a larger piston could be lost through the lines due to compression (?). Instead, because it was mentioned that better atomization occurs with a higher flow rate at the same hole diameter (which is my understanding), I assumed that there would be an excess of fuel across the entire speed range.

Best regards.
peter