95RedM

Just like the title says, I am wondering if ignition offset affects the values in my spark advance table. I don’t believe the timing marks line up correctly on my pulley/timing cover. With the motor timed at TDC, I require a ‘4’ ignition offset for my timing marks to line up when verifying ignition timing with a light and TunerStudio.

Someone suggested I get a digital timing light that can actually read the timing on the light, instead of the old crusty timing marks. My question is: does the ignition offset change the spark advance table? Meaning, not the numbers you see on the screen, but what they mean. So, would the same spark table with ‘0’ offset command the same spark advance as that table with ‘4’ offset? I hope that made sense, thanks for your time.

NB engine with cam/crank triggers

DNMakinson

iTrader: (3)

EDIT: YES The purpose of the OFFSET is to make the tables values be TRUE values, such that the spark will occur when the table says for it to. See further explanation in poset #5.

The table assumes that the offset is correct and that the spark would fire at TDC of the piston if your table has "0" in it.

It sounds to me that you are mis-understanding what "Someone suggested."

EDIT: everything also assumes that the TDC marks on your pulley and timing cover truly represent the location of the crankshaft has Pistons 1 & 4 at TDC.

DNM

95RedM

I don’t think the marks on my pulley is correct but besides that let’s say that my spark table says 15° at idle. With the offset at 0 it’s a true 15° advanced. What happens if it is set to, say 5. The computer will still say 15° but it will actually be at 10°? Or 20? Would it change every cell by the same amount or is in exponential?

I understand the numbers themselves won’t change on the computer, I’m talking about the actual ignition timing on the engine and what’s happening compared to what the ECU thinks is happening. How does the ignition offset/trigger angle setting affect it?

deezums

iTrader: (3)

You should need pretty much zero offset correction using a NB trigger wheel. I think it typically stays at 5. The NA has a CAS that rotates and breaks the link to the crankshaft, the NB does not.

A digital timing light is unnecessary, don't even need an advancing timing light.

DNMakinson

iTrader: (3)

This could get really deep, but I'm going to try to keep it in overview and hope the light of understanding comes on. On the side, you may wish to Google how a timing light works.

The MS tries to make the spark happen at the exact degrees of crank rotation BTDC of the cylinder in question that table calls for.

However, what if when the MS thinks the crank at 0* (TDC), the crank is actually 4*ATDC. Because, after all, there are a number of things that could cause that offset:
1) The holes in the timing wheel could be out of position so the wheel is not correctly timed with the crankshaft.
2) The position of the pickup could be off.
3) The time it takes the spark to actually fire relative to when the MS sends the signal could be other that what the MS expects.

So... It is important to make sure that the MS is properly cognizant of the TRUE crank position, not its ASSUMED crank position.

How can we make sure they are together. So that when the table calls for 25*BTDC, the spark really does fire when the crank is at 25* BTDC?

In the What If, we suggested that the MS mis-understands the TRUE position by 4* LATE. We want to know this and fix this.

Enter the timing light and the fixed timing and the Wizard with the OFFSET.

We tell the MS to give us 10* (Typically).
Then we put a timing light on Plug 1. It is really fast, and gives a flash of light exactly when the spark plug fires.
Let's say we have the Wizard set to "0" OFFSET.
If everything is perfect and correct, the timing light will show the "0" mark on the crank pulley aligned with the "10" mark on the timing cover. (remember we have timing set at 10* BTDC fixed)
BUT: Because of the MS being deceived by 5*, the pulley mark will not be at the 10* mark, but rather at the 6* mark, because the MS is firing 4* late.
We fix that by adding an OFFSET of 4*.
Now the pulley mark will be at the 10* mark, which is where it should be, because that is where we have asked the MS to put it.

Now we lock the OFFSET, and go back to running the table.

ALL OF THE ABOVE MS SETUP STILL ASSUMES 1 THING, THAT SHOULD BE KNOWN TO BE CORRECT.
It assumes that nothing is askew with the pulley mark or the timing cover.
To verify that, most people take a dowel rod and put it into cylinder 1 (remove the spark plug). Turn the crank until the dowel is at its highest height. That corresponds to piston 1 at TRUE TDC. Then look at the pulley "0" mark and make sure it is lined up with the "0" mark on the timing cover. If it is not, then the timing light, when used above, will lie to you. This must be fixed.... usually with a new Dynamic Balancer / Pulley.

DNM

95RedM

I think I found my answer, the trigger angle/offset makes changes in degrees. I wasn't sure if that was how it made changes. So for every "1" added (positive) it increases timing by 1 degree. The reason I asked these questions is because I just changed my cam seals and reset my timing and when doing that I noticed that when my motor is at TDC the timing marks show it to be about 4 or 5 degrees BTDC, instead of AT TDC. I did not notice this, and when i originally assembled my engine a few months ago, on the first start I set the offset to "5" because I was unaware that the timing marks didn't like up. SO, I was trying to find out if my entire spark table was 5 degrees more advanced than I thought it was. After timing the motor and setting offset to 0 I lost about 50hp, so one can only assume that the answer is YES my spark table was advanced 5 degrees further than I thought it was. I am on e85 and at 20psi my advance at redline was 21 degrees, so its safe to assume that number was ACTUALLY 26 as far as the engine is concerned. I've seen people run much higher than this, and I haven't had any issues. But I'm glad I caught it now before I made a catastrophic mistake later on.