Calculate injector start timing from engine RPM, pulse width, and desired end-of-injection angle, with crank degrees and cycle usage.

Injector Timing / End of Injection Calculator

Use the main mode to place end of injection in the cycle. Use the sweep helper to compare multiple end-angle targets at the same RPM and pulse width.

End of Injection Calculator
Timing Sweep Helper
Enter RPM, pulse width, and your desired end angle. BTDC and ATDC are interpreted around the 360° reference point. Results show start of injection, crank degrees consumed, cycle usage, and a quick timing-window note.
Compare a range of end-angle targets at one RPM and pulse width. This is useful when you want to test several candidate end-of-injection values without re-entering the same setup each time.

Related Calculators

Injector Timing / End of Injection Formula

The calculator converts injector pulse width into crankshaft degrees, then subtracts that duration from the selected end of injection angle to find the start of injection.

DurationDeg = PW_ms * RPM * 0.006
EOI_abs = EOI_input
EOI_abs = 360 - EOI_BTDC
EOI_abs = 360 + EOI_ATDC
SOI = EOI_abs - DurationDeg
CycleUsed = DurationDeg/720 * 100
WindowLeft = 720 - DurationDeg
  • DurationDeg is the injector pulse width expressed in crankshaft degrees.
  • PW_ms is injector pulse width in milliseconds.
  • RPM is engine speed in revolutions per minute.
  • EOI_input is the end of injection value entered as an absolute 0 to 720 degree cycle angle.
  • EOI_BTDC is the end of injection value entered as degrees before the 360 degree reference point.
  • EOI_ATDC is the end of injection value entered as degrees after the 360 degree reference point.
  • EOI_abs is the end of injection angle converted to an absolute cycle angle.
  • SOI is start of injection.
  • CycleUsed is the percent of the 720 degree engine cycle occupied by the injector pulse.
  • WindowLeft is the remaining crank angle in the 720 degree cycle after the pulse duration is accounted for.

In the end of injection mode, you enter RPM, pulse width, and a target end angle. The calculator converts the pulse width to crank degrees, converts the end angle reference if needed, and subtracts the pulse duration from the end angle to calculate start of injection.

In the timing sweep mode, the same formulas are repeated for each end angle in your sweep range. RPM and pulse width stay fixed, while the target end of injection angle changes by the step size you enter.

Injector Timing Reference Tables

Use these tables to put the result in context. Actual usable timing depends on the engine, injector location, fuel, air speed, wall wetting, and ECU strategy.

Cycle Used Timing Window What it usually means
Under 25% Ample The injector event is short relative to the 720 degree cycle. You have room to move injection timing.
25% to 45% Moderate Timing still has useful adjustment range, but start angle moves noticeably as pulse width changes.
45% to 65% Limited The injector is open for a large part of the cycle. Small fuel demand changes can shift start of injection a lot.
Over 65% Very limited Injector behavior is approaching static operation. End timing targets may become difficult to maintain.
Input Reference Conversion Example
Absolute cycle angle Use the entered value directly 380 degrees stays 380 degrees
BTDC from 360 degrees 360 minus BTDC value 20 degrees BTDC becomes 340 degrees absolute
ATDC from 360 degrees 360 plus ATDC value 20 degrees ATDC becomes 380 degrees absolute

Injector Timing Examples

Example 1: Find start of injection from an absolute end angle

You have 6500 RPM, an 8.5 ms pulse width, and a desired end of injection of 380 degrees absolute.

First, convert pulse width to crank degrees:

DurationDeg = 8.5 * 6500 * 0.006 = 331.5

Then subtract that from the end angle:

SOI = 380 - 331.5 = 48.5

The start of injection is 48.5 degrees absolute. The injector event uses 46.04% of the 720 degree cycle.

Example 2: Use an ATDC end angle

You have 3000 RPM, a 5.0 ms pulse width, and a desired end of injection of 20 degrees ATDC from the 360 degree reference.

Convert the end angle to absolute:

EOI_abs = 360 + 20 = 380

Convert pulse width to crank degrees:

DurationDeg = 5.0 * 3000 * 0.006 = 90

Find start of injection:

SOI = 380 - 90 = 290

The start of injection is 290 degrees absolute, which is 70 degrees BTDC relative to the 360 degree reference.

Injector Timing FAQ

What does end of injection mean?

End of injection is the crank angle where the injector pulse finishes. If the end of injection is set to 380 degrees absolute, the injector closes at 380 degrees in the 720 degree engine cycle. The calculator works backward from that closing point to find when the injector must open.

Why does RPM change the start of injection?

Injector pulse width is entered in milliseconds, but engine position is measured in crank degrees. At higher RPM, the crankshaft travels through more degrees during the same number of milliseconds. Because of that, the same 8 ms pulse takes more crank degrees at high RPM than it does at low RPM.

What happens if the calculated start angle is negative?

A negative raw start angle means the event begins before 0 degrees in the current 720 degree view. The calculator wraps that value back into the 0 to 720 degree cycle. For example, a raw start angle of -30 degrees displays as 690 degrees.