Tuning for Max Power - AFR vs. Ignition Timing?

[kstylianos]

Reading Loren's post the other day regarding the importance of proper ignition timing, AFR's, etc. got me thinking.....

Richening the AFR beyond max power output (POE 12.8-13.2) will allow more ignition advance without the fear of detonation. But richening the AFR beyond POE will decrease max power output.

Is more power gained from richening the mix (to a reasonable level) and allowing more advance timing, or finding POE for your particular setup/engine and set the ignition timing at a safe level (detonation minus a couple degrees)?

What is the general 'rule of thumb' here?

[jluetjen]

If finding max power was as simple as turning a richness screw, don't you think that it would have come that way from the factory?

[kstylianos]

that was not my question......

Bump?

[jluetjen]

Ok. 'Sorry for the sarcasm. I figured out that AFR = Air Fuel Ratio, but what is POE?

[kstylianos]

I've seen 'POE' listed as the AFR for max power.

[Randy Webb]

Rule of thumb? You'll need a properly designed & tested detonation sensor in each head (or on each side if you _know_ a certain head in each bank always goes first), a good computer, and a way to quickly adjust the parameters. The factory can do this (and some manf.s have done so) but few if any tuners can do it.

So, I'm not sure what your question means.

[Lorenfb]

Agreed! NOT a simple effort and not a "game" to be played on a PC by "whiz
hackers".

[TimT]

When we set up cars on a dyno, we first tune for AFR, we get the AFR somewhere between 12.5-13.5 for maximum potential power.

Then we go back and adjust timing at each load site. Timng is adjusted to provide max torque at each load site.

For example we run the car to 3000rpm, then dial load into the dyno. then while holding at 3000 rpm the timing is adjusted to the point where max torque is seen, then begins to fall off. The timing is then backed off to the point we found max power.


If you have a system with a knock sensor installed you can leave the timing at the point of maximum power. If not to give a margin of safety we back the timing off a touch from the instantaneous max we observe.

[Lorenfb]

TimT is right on! Methodology described is the way performance chips and
all tuning development should be done. No game playing here.

[Mike Feinstein]

Yes but...wouldn't there need to be a reasonable safety margin implemented in the event of climate changes (heat), fuel quality, etc? Conditions in July at the track may not be the same as those on the dyno last December. Even with knock sensors, they react to detonation by retarding timing which reduces power...not the intent.

I'm no expert but it seems that it would be difficult to optimize performance for all conditions.

[TimT]

it would be difficult to optimize performance for all conditions

It IS difficult to tune for optimum performance in all conditions!! The factory ecus are set up with numerous comprimises They have to bother with efficiency, emissions, questionable fuel qualities,driveability, etc. Many others have mentioned that Porsche didnt leave alot on the table, thats why its so hard to find extra power when chipping the ecu.

Ive set up a number of cars with EFI for track use. We know what octane fuel we are going to be using every time out etc. So we tune for maximum power. Most of the ecu's we deal with adjust fuel/spark etc based on ambient temp, rpm,load,manifold pressure (boost or vacuum)

One off the comprimises made is retarding timing at the point of max power seen on the dyno. There are lots of tricks used when tuning the cars on the dyno, and Im still learning them all the time.

[kstylianos]

Thanks Tim! Thats just the type of feedback I was looking for.