Tuning: Factory vs. Aftermarket & FAQs

Hello everyone,

I dug out the MTZ article (issue 12/95) again about upgrading the 1Z engine to the AFN.

It contains, among other things, some interesting passages on the topic of chip tuning (in essence).

If one attempts to increase the power of a 90 HP TDI engine to 110 HP without making any hardware changes, the injection times must be extended to an unacceptable level.
Extending the ignition timing by 2° KW (degrees crank angle) results in an increase in exhaust gas temperature from 750 to 880°C, and the smoke number rises from 2.2 to 3.5 Bosch.
If the injection is started 2° KW earlier, the peak pressures increase from 140 to 165 bar, and noise and NOx emissions also increase.

Both times, the often-promised 81 kW was not achieved, but "only" 79 kW.

For the AFN engine, nozzles with a bore diameter of 205 instead of 186 were used (as is well known). To compensate for the resulting deterioration in atomization at low speeds and partial load, the fuel pump's delivery rate was not only adjusted to the higher volumes but also to the larger nozzles.
A comparison diagram, including a "plunger speed" labeled "C1000" in m/sec, is shown. What exactly does this plunger speed represent?

Interestingly, the tuners don't seem to be deterred by the alleged illegality of extending the injection times. Or does anyone know of a tuner who, in order to increase performance for on-road use(!), doesn't just extend the injection times, but also installs larger injectors?

According to what criteria (or safety margins) could the MTZ (presumably a regulatory body) have possibly assessed the inadmissibility of extending the injection period?

Overall, based on the MTZ article, the jet swap seems to be "closer to performance tuning" than the generally common practice of extending the injection times.

On the other hand, larger nozzles, with the same injection start, may increase the peak pressures again, as the diesel fuel is injected more quickly (volume per degree of crankshaft rotation), and thus a given amount can burn during a shorter time.
Is this type of increased peak pressure less stressful for the material compared to a pre-injection start?

One more strange thing:
In a diagram illustrating the effects of chip tuning, the standard full-load injection duration for the 1Z engine is specified as ranging from 14° BTDC to 22° ATDC, totaling 36° crank angle.
In the pump's timing diagram (cam profile), the injection start is specified at approximately 1° and the injection end at full load is specified at 13° BTDC, which corresponds to a total of only 24° CA.
How does that fit together? Or, to put it another way, how long (in degrees of crankshaft rotation) is fuel actually injected into a TDI engine?

Deleted upon request.

diesel.gustav wrote:

1.) The C1000 represents the velocity profile of the distributor piston at 1000 pump revolutions. It is a frequently used reference value in pump applications.

Hello Gustav.

Ah, yes, now it's clear. I couldn't interpret the "1000".

Quote:

3.) Regarding your comment: "changing the injectors is closer to engine tuning" than the commonly used method of extending the injection time." This was not about "tuning" but about further development. The larger injector nozzles were only a small part of it. The entire injection system, the EDC, the turbocharging, and even the engine itself were modified.

Yes, of course. But at the moment, I was only concerned with the aspect of increasing the injection quantity, which is often already the whole (subsequent) tuning process.

Quote:

4.) Regarding the full-load injection duration, the two images have little in common. They definitely represent two different operating states, because C1000 means 2000 RPM on the engine, and if, as in the other image, it refers to power, it means the rated power speed of 4150 RPM.

Ah, it's starting to make sense.
At 2000 rpm , the full-load injection duration in °KW will be approximately double the pump delivery duration in °NW, so about 24° KW.

The increase in injection angle at Pmax = 4150 rpm to 36° KW is mainly due to the pump characteristic curve (extension of the injection angle duration at high speeds due to "too small" nozzle bore diameters, etc.) - and the small change in the effective full-load quantity between 2000 and 4150 rpm is considered negligible.

Thank you for your insightful answers .