A question about theory of timing.
Why is it that we are supposed to start
pulling timing out when we pass peak torque (or somewhere close to that point).
What exactly is the reason for this.
I'm tuning, and trying to figure a good timing curve for my chip... thanks for any help.

 

Always pulling timing out after peak torque doesn't make sense to me- a couple of bins I checked for smaller bore motors always put more advance in after peak torque. This would seem to make sense, because the VE's decrease after peak torque, so the charge density and therefore the rate of pressure rise (not burn rate) would be slower if ignited at the same angle as at peak torque, and the time to burn is less than at lower rpm.

You would think the faster it's going, the more advance angle you can stand (as a rule of thumb), but bigger bore motors don't always have spark maps like this. Maybe due to turbulence issues.

My $0.02 worth.

John

 

Well thats not always true at all, most non efi cars are at full adv. at highest rpm.
As is the case with my timing tables, I have highest degrees after 4500.
But one reason you may see the adv. get higher as opposed to
lesser is piston speed increases therefor mechanically reducing effects of advance.

 

Peak torque is the most effiecent point.
Tuned corredtly you can get your best BSFC there.
Just to be obvious, it is PEAK Torque.

Now, depending on motor configuration.
And there are two typcially, ie one street and one race.
So both will take different paths, with the street maintaining the same timing as at PT, whereas the hot street/race will want to add some timing after PT. BUT, exhaust back pressure, and the self EGR-ing effects of the cam can also tweak the game some.
And this all can lead to where ya start adding timing to avoid detonation.

And none of this even broachs the gas formulation as it varies from summer to winter, and area to area. Since the additive packages change.

 

This is a new ironic anti-detonation strategy, is it Bruce?

John