Pulling Timing questions

[david-b]

Been thinking about some stuff and how the engine will pull timing if the car starts to lean up too much. How does it do that though? I could see if the car had adjustable cams and the ECU modified those or whatever, but how can it do it electronically? Everything is solid in place so what changes? Spark?

[LandoAWD]

Timing is awarded based on ECU calculations on preset tables. These tables can be modified, but some form of this always takes place.

The ECU sees everything and makes its decisions. Factors include knock, intake temps, etc.

[david-b]

I understand what it looks at to adjust it based on these variables, but what exactly is it pulling? It's not physically making changes to pull out timing, so how is it doing that?

[LandoAWD]

Timing advance is not base timing.

[SilvrEclipse]

The ECU will advance the ignition timing and when it gets knock it retards the ignition timing. It doesn't have anything to do with the timing of the valves. It changes when the spark goes to the plugs.

So when people say the ECU is pulling timing that means that the ECU has retarded the timing some because it was seeing knock. If you log your timing with your datalogger you and do a 3rd gear pull you will see the timing go: 17..18..19..20...21. I believe the 420a will hit 21degree advance, but I may be wrong. Look for dips in the timing curve when the numbers goes down slightly and then it may go back up. This is where your seeing knock and need to richen the car up.

[david-b]

Ok so the timing change is just done by spark then. So on the MSD units that advance and retard timing, it basically just tells the spark to fire earlier/later? Wouldn't adjustable cam gears be pointless with something like that then?

[SilvrEclipse]

This is correct. You would be able to tell the spark to fire earlier/later.

Cam gears have nothing to do with the ignition timing. The cam gears are used to adjust the valve timing. Most people just use them to tune their upgraded cams some. Some cams have more valve overlap than others which you dont want on a boosted car. On a NA car a little overlap is good.

[david-b]

Originally Posted by SilvrEclipse

This is correct. You would be able to tell the spark to fire earlier/later.

Cam gears have nothing to do with the ignition timing. The cam gears are used to adjust the valve timing. Most people just use them to tune their upgraded cams some. Some cams have more valve overlap than others which you dont want on a boosted car. On a NA car a little overlap is good.

Well I know they have nothing with ignition timing, but say if you want to retard the whole timing, you can do via the units or cam gears.

[SilvrEclipse]

Originally Posted by david-b

Well I know they have nothing with ignition timing, but say if you want to retard the whole timing, you can do via the units or cam gears.

No thats not right. Ignition timing related to how close the plug fires to a cylinders TDC. So the more advanced your timing is the close the plug fires to when the cyinder is at TDC. When you retard the ignition timing your cylinder is further from TDC when the plug fires.

All the cam gears do is adjust when the valves open. Now if you adjust the exhaust cam enough it may alter some things because of the CAS but I believe the ignition timing only runs off the crank angle sensor.

Someone correct me if Im wrong about the way this works.

[gthompson97]

No you basically got it all. Dave, I know it sounds noobish, but you should look into some books about simple engine cycles, components, and stuff like that, it'll really help you understand the basic basics.

[kjewer1]

Another key point to remember is that when setting "base" timing, you aren't really setting timing. You're synchronizing actual physical timing with the ECU's perception of timing. The ECU has full control over timing advance. In reference to post #9, moving the cam with the CAS on it will affect base timing on all 1Gs, but not 2G turbos. No idea about 2g NTs.