timing issues

[odd boy]

Hi,

Any one knows when I have to advance or retard the spark, I've noticed that people advanced the spark at low RPM and high grm/cyl. And did some retards to the sparks at high RPM and high grm/cyl.

Also, let us assume that the peak torque is at 5000 rpm, should I advance the values at 5000 rpm? if yes at which grm/cyl.

[cmitchell17]

I think timing should look like an invearse of the ve table. So more airmass needs less timing (Peak torque) Low airmass needs more timing (Low rpms very high rpms)

[joecar]

Higher cylinder airmass represents higher load... higher load usually requires less timing... there are various reasons for this, one of them being that the burn rate is the fastest... which means too much advance will allow knock to occur... but it's not all as simple as this.

At peak TQ you reduce timing (and set mixture richer)... as you move away from peak TQ you can increase timing (and set mixture leaner).

You will see this in various tunes, see www.holdencrazy.com for examples.

[The Alchemist]

Hi, this is something you definately do not want to play around with if you are just "learning" . In more advanced stages of learning it may be OK See the holdencrazy site for examples of modified tunes to get a handle on timing maps with different setups before you start playing with fire
The factory maps can be miles out but the later SS "VZ" holden timing maps ( not the clubsport models ) are actually very good and can be used as a good base . See how these compare to the spark map in your car....
Mike

[cmitchell17]

Ive been thinking about timing more. If I could run about a 13-13.4 AFR at wot (Which Ive heard makes the best torque and going richer than that is just to lower egt's)

So i wonder what would happen by running about 3-5 degrees less timing at wot and running about 13-13.4AFR. Becuase at that afr I don't think you would need that much timing becuase the burn rate is faster.

I don't even see why the richer mixture makes more torque than stoich? Isnt anything richer than stoich just going to be wasting fuel? Ive heard that the slightly rich mixture ensures that the all the oxygen molecules are used for combustion. But why wouldent they all be used at stoich? Is their not enough time for complete combustion at high loads and rpms?