360 degrees base timing offset

I've seen in numerous videos that it is "normal" to have the timing offset off my 360 degrees due to the setup of the car...

...but what I can't get my head around (and I've done a lot of thinking and googling on this) is why it happens.

We've setup many cars on older Motec ECUs and they've always been +/- a few degress (< 10) on the base timing offset.

Now we're doing more work with Links, we're having a few cars come through where it's out by a full rotation... obviously the cars run fine afterwards... but we're trying to work out why it's different on car to car - what has been setup differently to cause this?

All the cars are 3SGTE MR2s running standard distributer.

It just comes down to the relationship of the camshaft position sensor, whether on the camshaft or the distributor, to the #1 firing crank rotation.

The camshaft sends the trigger signal every two revolutions, and the crankshaft position sensor every revolution, so the ECU may have to add another revolution to correct the #1 firing relative to the cam' signal for #1 firing TDC, rather than #1 overlap.

Hi Gorg,

Thanks for your response. Based on this, I did some digging into how the innards work on the standard 3SGTE distributor works.

There are 3 outputs:

NE - pulses on a 24 tooth wheel

G1 - pulses on a single tooth when #1 is at TDC for ignition

G2 - pulses on same tooth, offset by 180 degs, so when #1 is at TDC for exhaust (360 degs from crank perspective)

Therefore, the cars we've had coming through must be mix and matching G1 and G2 for some reason. I wonder if Toyota changed the pin layout on standard ECU over the years which means plug and play units pick this up differently depending on age.

Anyway, thanks very much for your help.

Forgot, some distributors with a slot drive can be fitted in two ways, 180 degrees from each other, others with drive gears can also be fitted out of phase - don't know if yours may be one of them?