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Discussion Starter #1
At what degree of engine rotation do I have the Cam sync trigger in relationship to the ignition trigger? I'm using a MSD 7535 box for the ignition control and a Holley Dominator EFI for the fuel control. And I'm running a Jesel belt drive distributor with the cam sync pick up off the rotor drive.

I assume I would want the cam sync to trigger before the ignition fires... Correct? And if so, what degree before ignition do I set it?

If my total timing is lets say 35 degrees BTDC, and under boost, it could go as low as 10 degree BTDC, or even more, where would I set my cam sync?

I posted this question on the MSD tech forum and all they said was "total timing." Not very elaborative and it does not seem right.

If I set my cam sync to trigger @ 35 degrees BTDC and then I pull timing and start firing before it sees that 35 degree cam sync event... it sounds like that would not work correctly, or do I have that wrong?

415 Posts
I think the cam sync signal has to be a minimum of 70 degrees before the crank signal on the compression stroke...
And it gives you like a 100+ degree window,

1,144 Posts
I found this a few weeks ago. great Holley website information


A cam sync pulse is required if you are running sequential fuel injection. This tells the ECU which cylinder is cylinder #1 (or the first cylinder in the firing order as entered in the software). The following describes setting this up for a “one pulse per fire” crank input as well as a “60-2” crank input.

2.1 Cam Sync setup when using a “one pulse per fire” crank input

For a "one pulse per fire crank” signal (e.g. a 4 pulse crank trigger on a V8), the cam sync signal must occur in a specific range to properly identify which cylinder is cylinder #1. If this is not done properly, individual cylinder trims will not be performed on the correct cylinder, or worse, if using individual coils, the wrong cylinder will be fired, potentially damaging the started, flexplate, or worse.

The best way to determine the proper range is by using the following basic formula to determine the crank angle range that the cam identity can occur.
An example is give afterwards along with a table that has certain combinations already calculated.

Cam sync location (degrees BTDC #1) = "Ignition Reference Angle" + “A” + (“A” / 2)
“Ignition Reference Angle” = Taken from Crank Sensor Setup in software
“A” = Angle Between Crank Pulses (crank degrees between triggers on the crank sensor)

“A” for a 8 cylinder = 90°
“A” for a 6 cylinder = 120°
“A” for a 4 cylinder = 180°

Using the formula above, plug in the “Ignition Reference Angle” you are using and the proper “A” value depending on the number of engine cylinders.
The location calculated is the “ideal” location and can vary +/- 30 degrees or possibly more.
If you are out of this range contact Holley Tech Service for options.

Example - 8 cylinder with a Ignition Reference Angle of 60°
Cam Sync Location = 60 + 90 + 90/2 = 195 degrees BTDC #1

Cam Sync Location = 60 + 90 + 45 = 195 degrees BTDC #1
195° would be the centrally "perfect" location for this specific example.
However, this location can vary by +/- 30 degrees from this nominal target value with no issue.

Number of Cylinders Ignition Reference Angle Cam Trigger Location Range (BTDC #1)
4 60 330 +/-30 degrees
6 60 240 +/-30 degrees
8 60 195 +/-30 degrees

NOTE: If it is mechanically not possible to install the cam trigger in the proper location, the engine firing order can be changed to compensate.
For details on this, contact Holley Tech Service at 1-866-GOHOLLEY.
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