DOD timing

[waynehartwig]

Why are the tables different from the high/low octane tables? Do they need to be? Or can I increase timing like you would for high/low tables? Or better yet, can I just situated the high/low tables and then copy them over?

[Aaron_Provost]

I would also like to know the answer to this

[waynehartwig]

Bump to try for an answer....

[LazMan]

Here is how Ive "quickly" tuned DOD spark tables in the past.

1. Disable DOD and tune the part throttle timing.
2. Copy the standard tables to the DOD tables and enable DOD.
3. Reduce timing where I have knock. Be sure to reduce "more" than you need to, about 1.5 to 2 degrees.

Usually you cannot run as much DOD timing as you do v8 timing because well - you're dragging 4 cylinders along. Think about it. However, you can always run more timing than most engines bring stock.

Additional timing on DOD is far more effective than screwing around with the vacuum settings - though you usually have to raise the 6% throttle enable value (TPS MAX) to somewhere around 8.5%.

[Texsrt4]

you are not really "dragging" the cylinders. The only "drag" is the parasitic loss caused by the rings dragging on the bore. The balance of the motor is such that one cylinder pressurizes at the same time that another depressurizes. This net force is 0

[MyLS1Hauls]

The reason why you have to run lower timing in DoD is due to the excessive load on each cylinder...You now have four cylinders moving the car, not eight, so the load is essentially doubled. Add more load, and you can/will induce knock.

[LazMan]

you are not really "dragging" the cylinders

I don't disagree with you Texsrt4 nor your premise that you're not dragging the cylinders. The trapped air charge acts as a spring that is continuously compressed and expanded. I touched on the wrong thing when it comes to the timing differences.

However, the net force is not zero as this is not the only force involved. There is more than just the friction from the rings but mainly the additional reciprocating mass, plus the friction from the rings + bearings + collapsed tappets (however slight) = the fact you have all this STUFF basically being moved around but doing no positive work means that you are losing/wasting energy.

Therefore a 3L I4 will get better MPG than a 6L V8 in V4 mode because its simply designed and built differently.

Nonetheless, even if we ignore these differences, which are not monumental and ok to ignore, the timing requirements of our V4 will be much closer to those of an I4 than those of a V8 - hence the different timing tables. The 4 cyl can be 'lugged' easier since it has slightly less than half the torque of V8 mode - so it will usually do better at slightly less timing than V8 mode. GM uses a LOT less timing - i guess to protect their warranties.