Piston Seizure: 10 Cent Tuning Risks

Hi everyone,

Has anyone actually experienced or seen a seized piston caused by damage from a cheap '10-cent' tuning modification?

My thought is: Without increasing the boost pressure, you would only be able to utilize the 20% excess air if you don't want to use a smoke box. This implies that the injection amount should not be increased by more than 20%, or the injection duration (assuming a linear relationship) should not be extended by more than 20%.
The injection occurs approximately at +/- Top Dead Center (TDC). This is also the area where the piston has the lowest speed (stroke) relative to the crankshaft's rotational angle.
If you increase the injection duration by 20%, does the piston actually start moving downwards again significantly? Isn't it also true that the injection start is advanced slightly at higher engine speeds or under full throttle?

If the actual injection moments (degrees before/after TDC), the injection duration, and the engine speed were known, it would be possible to precisely predict whether the piston is already on its way down during a prolonged injection, and also how far it has traveled.
With the extremely high injection pressures used today, a 'long' injection duration is not actually necessary.
I suspect that we're only talking about microseconds here, and that piston seizure only occurs with extreme tuning modifications (e.g., increasing power from 90 hp to 150 hp).

Perhaps this topic is unnecessary and a duplicate. If so, it can be deleted.
It would be really interesting to know whether the piston seizing is a good piece of mechanic's jargon or actual reality...

Regards,

Eike.

Hello!

I read something about a crank angle of approximately 20-25 degrees for the injection duration in a common rail system with 870 bar pressure. It was an article about the influence of the bowl shape on the combustion process in a test engine. The absolute injection duration was 2 ms! (Let's do a quick calculation to see if that's possible: 2000 rpm = 33 cycles per second = 30 ms. So, 2 ms corresponds to 360 degrees / 30 * 2 = 24 degrees at 2000 rpm).

With double the engine speed and a constant injection time, the crankshaft angle also doubles.
I once suggested connecting an oscilloscope to the injector driver to directly measure the injection duration in our TDIs, but I haven't tried it myself.

Regards,
Udo.