Spark timing for optimum fuel economy

[Highlander]

I am very sorry Highlander but you have been mislead

No you don't advance that far at idle. Idle is combination of airflow and timing. I am not talking idle tuning. I am talking driving conditions. You tune for maximum torque at any given rpm and map for best economy and performance. Tuning LS1s I have always been able to get fueling better on the road then dyno 100% of the time you cant get road conditions on the dyno and if you can you have to compensate for it, and trust me I have 1000s of hours of logging. Ramp rates drastically change and alter fueling to the road by a hole 1 afr point at WOT generally. Best to use both dyno and road. Of course you need time to do this and usually at your own expense as it is faster to do it on the dyno then the road, Hence why so may self tuners can tune there car better then any shop, takes time and logging and temp variation to get it right. Many cars I have done have exceeded over 800km per tank by doing so.

Also ur statement there is no way knowing peak VE is far beyond the truth. We have efilive and good PCMs, you can log peak g/cyl in the log and it will show you right there and then. This is also backed up on the dyno. A load dyno at that. If to much timing is put in peak VE drops off dramatically. Its about using the tools at hand and having the knowledge and experience to carry it out. Hence why my peak dyno number tune and best ET track tune vary by a long shot.

I am stating a fact, its correct from a physics and chemistry point of view. And its proven. A dyno can't see this you and I can't. But a well tuned engine will have peak cylinder pressure occuring at the same time. If its to late you lose torque to early you lose torque. When you spark an engine changes as MAP and rpm varies. Maybe the average mechanic cannot comprehend this but its science and we can go much deeper if you like.

You can argue with me all day, but I listen to doctors in physics. I listen and learn.

Again argue the point with me. But there are to many variations to look at. Simply my point is peak pressure always occurs at the same time hence at 100kpa at low rpm your engine requires x deg timing at 5000rpm it needs more advance to fire earlier to ensure that peak cylinder pressure is occuring at the correct moment.

Hymey... everything you say in this thread is correct... My arguing point is. if you get max cylinder pressure you get max torque and the only true way to find this out is in a dyno...

Using efilive, i haven't had a car have a different A/F on the dyno than on the street and I test them ALWAYS.. they are pretty much DEAD ON.

On Fords, they usually get a tad richer on the street.

My point about advancing timing @idle was to show you that you could advance timing way beyond your max torque output and NOT get any knock.

One thing would be: could you post your HP curves for your best ET vs your best dyno graph?

Maybe the climate on the dyno changes a lot. It has always been my purpose to put the car as far close to street conditions in the dyno to get an accurate tune. Hence why I don't get much issues with it.

[ringram]

Simply my point is peak pressure always occurs at the same time hence at 100kpa at low rpm your engine requires x deg timing at 5000rpm it needs more advance to fire earlier to ensure that peak cylinder pressure is occuring at the correct moment.

Yeah, my understanding is that you want this point to be around 14* ATDC (engine dependant)