QUESTION ABOUT INJECTION TIMING

HELLO. I am learning tuning. i want to practice on ford transid and sutom diesels, 2.2 (ecu is sid208). my main quesiton is this:

in this course it was said that :

in order to count the mseconds of rpm, we have to divide 120 by rpm first.lets take 1000120 / 1000 = 0.12 = 120 msso 120 ms is 720 degree crankshaft rotation (full). 720 / 120 = 6 deg, so at 1000 rpm, 1 msecond is same as 6 deg crank rotation.lets take 4000120 / 4000 = 0.03 = 30 ms30 ms = 720 degr rotation, 720 / 30 = 24, so at 4000 rpm 1 msecond is same as 24 deg of rotation.i want to ask, why 120? isnt rpm measured in minutes? so should not it be 60?also, for ford transit diesels, what is the best time to inject? always full injection before top dead center? i am trying to learn stage 1's, so should i focus on full injection before top dead center? thanks in advence

Nale,

The 120 is correct because you’re looking at a full 4-stroke cycle, which is 720° of crank rotation, or 2 full crank revolutions.

60 / RPM gives you the time for one 360° revolution.

120 / RPM gives you the time for the full 720° cycle.

So at 1000 rpm:

120 / 1000 = 0.12 sec = 120 ms

720° / 120 ms = 6° per ms

At 4000 rpm:

120 / 4000 = 0.03 sec = 30 ms

720° / 30 ms = 24° per ms

An easier shortcut is:

degrees per ms = RPM × 0.006

So 1000 rpm = 6°/ms, 2000 = 12°/ms, 3000 = 18°/ms, 4000 = 24°/ms.

On the injection timing question, I would not use “finish all the injection before TDC” as the goal. That can be dangerous and loud

What matters more is where the combustion event is happening relative to TDC. Injection timing is not the same thing as combustion timing because there is still ignition delay after SOI.

It is completely normal for the main injection event to continue past TDC under load.

For example, say you’re at 3000 rpm and duration is 1.0 ms. That’s about 18° of crank duration. If SOI is 10° BTDC, EOI would be roughly 8° ATDC.

If you add fuel for a Stage 1 and duration increases to 1.4 ms, now you have about 25° of injection duration. If you leave SOI at 10° BTDC, EOI moves out to roughly 15° ATDC.

That is where you need to start thinking about whether some additional SOI advance is appropriate. Not necessarily to get EOI before TDC, but to stop the whole combustion event from getting pushed too far late.

Too much advance can increase cylinder pressure, pressure rise and NOx. Too late and you generally get more smoke, EGT and worse efficiency.

So for learning Stage 1 tuning I’d look at the whole relationship:

requested torque → fuel quantity → rail pressure → injection duration → SOI → approximate EOI

Hope this helps,

Nick

Thank you