Optimizing Timing

[neil]

Hi,
Could someone take me through the process of optimizing the timing tables after completing the AutoVE process?
I don't have access to a dyno.
Any help would be much appreciated.

Regards,

Neil.

[cmitchell17]

I used a blend of my stock high octane table and the optimal timing table.

But I was stock, stock heads cam. So I dont think that would help you.

Timing confuses me the way it ramps up to peak torque then stops.

I can't tell a diffrence when I changed my timing at all so I trust that the optimal timing table is a good guide.

[SinisterSS]

Peak torque is where there is maximum pressure inside cylinder. If the pressure is too high, the air:fuel mixture will begin combustion before the spark plug ignites the mixture and you'll see the knock show up in the data.

Backing timing off at peak torque is to maintain maximum cylinder pressure without stepping over the line.

[johnsZ06]

Without a dyno it's difficult.

Basically, what I do is tune for mileage while in closed loop and I add timing during WOT until I see KR and then I back it off a few degrees. It's crude but seems to work OK with a dyno.

[redhardsupra]

Without a dyno it's difficult.

Basically, what I do is tune for mileage while in closed loop and I add timing during WOT until I see KR and then I back it off a few degrees. It's crude but seems to work OK with a dyno.

that's the oldschool method that really does not apply to modern cars.
I tuned one GTO (heavy but with good heads) which made max power commanding 22* at peak torque, but on the dyno it wouldnt knock till 34*. on the street it would knock with anything more than 25* in higher gears. do not assume that the highest value without knocking is the best number. This isn't blackjack ;)

besides, on the street you really cannot do timing. timing dependent power output changes can be very subtle and drown in the noise you get in data gathered on the street. you cannot hold the engine at a constant rpm/map while adjusting AFR and spark while watching the HP drop or rise.

a good dyno (not inertia one) allows you to limit the road noise and control your environment to the point where the subtle changes become visible and clear. on the road you can change some values and watch the time traversing the same speed interval change, but in the end, you're going to be changing an entire range of timing values, not every individual one, so you dont know which cell had a positive and which had negative effect on the final outcome.

[cmitchell17]

Why is the optimal timing so high?
The LS motors are probaby diffrent. But for the truck motors timing is 30 degrees at high rpms, high airmass? Timing is all in by 3600rpm at 29 degrees.

Did GM really test this as the best timing. Is the diffrence in heads and combustion chamber responsible for the high timing?

[redhardsupra]

trucks have lousy heads and low compression so they can run on low octane. that can take a lot more timing. a more 'sporty' setup with a cam that allows for a lot of airmass, especially when combined with good heads, dont need much timing at all. think of a good high compression NA as a lousy low boost FI--they can make a good amount of power even on very low spark. high effective compression allows a very quick flame front propagation, thus it takes a short time for a complete combustion.

[cmitchell17]

My old 95TBI would knock at WOT with 23-24 degrees of timing. This was with 93 octane. I would guess that it was my knock sensors.

Even with my 5.3 I can hear it knock with 26-29 degrees of timing with 93 octane. The knock sensor is also not consistent and does not show what I hear. I think the IATs have a lot to do with my knock too.

My only sometimes make sense to me, and I never see what I want to see.