Is my Trigger Pattern supported ?

[fivepoint6]

my V8 has the following trigger pattern.
A 12V crank signal (8 pulses per cycle), neg. edge at appr. 48° BTDC, pos. edge at appr. 6° BTDC.
A VR-cam signal appr. 44° BTDC#1.
I'm planning to do fully sequential fuel only (LPG).
Is this pattern supported by VEMS ?

[VEMS]

Hello Fivepoint6,

Yes your trigger pattern is supported (simple one pulse per ignition event on v8), primary trigger = HALL (8 tooth) secondary trigger = VR (single tooth).

Best regards, Dave

[fivepoint6]

Hello Dave,

glad to hear that.

I assume I cannot use the neg. edge from the crank signal because the cam signal is too close, right ?
The pos. edge is only 6° BTDC, will that work ?


Regards,
Jan

[mattias]

With the primary trigger being Hall type you can try using rising instead of falling to offset the cam sync edge.
With VR triggers the rising edge is mandatory (zero crossing negative to positive) so it is where it is. A switch of polarity would be beneficial in this case, no?

[fivepoint6]

help in vemstune says tdc after trigger should be 60 to 127.
So i wonder if 6 will work.

[mattias]

Use the other trigger edge to make it 48° .

[fivepoint6]

if you look at the scope pattern, the cam signal comes right after the falling edge of the crank signal.
Are you sure, that will work ?

[VEMS]

Hello FivePoint6,

if you look at the scope pattern, the cam signal comes right after the falling edge of the crank signal.
Are you sure, that will work ?

Yes, will certainly work. The rising edge is your safest bet as it is a lot less close to sectrig, 6 deg BTDC means 6+720/8=96 deg BTDC on next cylinder to fire, im sure the distributor on your v8 can also be rotated somewhat; I would recommend 15 degree, that would bring tdc_delay down another (offset whole cycle with) 30 degree resulting in trigger point (rising edge) 96-30=66 crankdeg BTDC, perfect.

Best regards, Dave

[fivepoint6]

Hello Dave,

thank you.
But now I'm totally confused.

Do you mean the falling edge (48° BTDC, very close to cam signal and cam signal is after falling edge)
or the rising edge (6° BTDC, 38° after cam signal) ?

Regards,
Jan

[VEMS]

Hello Jan,

Do you mean the falling edge (48° BTDC, very close to cam signal and cam signal is after falling edge)
or the rising edge (6° BTDC, 38° after cam signal) ?

I am referring to rising edge after cam signal at 6deg BTDC on the cylinder you measured, but also 6 + 720/8 = 96 deg BTDC for the next cylinder to fire in sequence. The 6 deg is obviously not within the 60-127degree tdc_delay range, but when we adjust the ignition coil sequence (or has it got distributor ? in that case we have to rotate it some more) we can correct it.

In any case, the rising edges (any) have the biggest difference (in crank degrees) between crank pulses and cam pulse which is the preferred choice.

Best regards, Dave

[fivepoint6]

thank you Dave