Too Much Timing?

[Lumpo]

When you guys tune timing do you just keep adding and adding till you see KR and then back it off or is there a limit? Right now im tuning my 2003 Tahoe 5.3 and ATM im tuning part throttle timing to gain some MPG. I already added 10* of timing to part throttle with no KR but i just want to be sure im not adding to much. So is the method just keep adding as much as possible without KR?

[carlrx7]

make sure if you add the timing, you are adding it to spots on the table where you are using it. 10 degrees is alot

[eficalibrator]

At part throttle, the knock limit is usually well beyond the MBT point. You'll find that you can add a lot of extra timing at part throttle without getting knock. The problem is that you're also not getting any extra torque out of it, in fact quite the opposite in some cases. Just because you CAN add more timing doesn't mean you SHOULD in some cases.

[Lumpo]

I only added the timing in the cells where they settle at between 0-65 MPH and it already seems like my MPG has increased by doing this. So i can actually add to much timing even when no KR is present and actually lose power? So then whats the best method for adding timing?

[Lumpo]

Here is what i was able to add without any KR to my stock Tahoe 5.3...Notice where i added most of my timing is between 1200-1800RPM
and .20-.44 G/CYL. This chart is the difference from stock to my current timing table...

[MikeGyver]

... So i can actually add to much timing even when no KR is present and actually lose power? So then whats the best method for adding timing?

That's what efi c. is saying. I guess that all of us who are in the same boat concerning this, messed up by not buying steady-state dynos before buying HP Tuners!

[Lumpo]

So without the use of a Dyno how do you guys adjust part throttle timing for mileage?

[eficalibrator]

I only added the timing in the cells where they settle at between 0-65 MPH and it already seems like my MPG has increased by doing this.

Yes, with a bigger cam (or some other mods) this area will typically need more timing than stock to get back to MBT with the extra EGR from cam overlap. If you were not on MBT timing previously, adding timing to get there will increase fuel economy.

So i can actually add to much timing even when no KR is present and actually lose power? So then whats the best method for adding timing?

Yes. When you add timing beyond the MBT point, you lose torque/power. There's a plateau of torque near MBT where you'll see pretty much the same torque +/- a few degrees from MBT, but adding more will drop it even before you start to experience knock.

The best method to determine optimal timing to hit MBT is in-cylinder pressure transducers. That's REALLY expensive and difficult to find the equipment, so our next best tool is a load bearing dyno where we can physically measure torque while we're adjusting timing.

That's what efi c. is saying. I guess that all of us who are in the same boat concerning this, messed up by not buying steady-state dynos before buying HP Tuners!

You don't need to buy one, just rent time on one.

So without the use of a Dyno how do you guys adjust part throttle timing for mileage?

See above. An hour of dyno time costs less than the three weeks of fuel you'd burn wandering around the back roads guessing at things and you'd actually have the data to prove that you got it right. Remember, you don't need to hit every single point in the table, but grabbing a few points and spotting the trends goes a long way toward nailing down the right spark map at part throttle.

[Higgs Boson]

Greg isn't it true that on today's E10 93 gas that you actually will get knock before MBT?

Is this something only really need to worry about on race gas?

I feel like mine will knock pretty quick with timing increases but on C12 I can add 15 degrees of timing (and it is definitely faster) without knock.

[eficalibrator]

E10 vs E0 isn't really the issue so much as octane number. Octane is the anti-knock index, so it applies to a wide range of fuel blends.

For this discussion, we were talking more about part-throttle timing than WOT. At light loads, it's much easier to find MBT or go past it without hitting the knock threshold. As loads increase (especially at WOT), you'll typically hit the knock limit on pump gas before you find MBT. This is why higher octane fuels allow you to make more power because you're advancing toward MBT. Going past MBT in any case is generally not desirable.

[MikeGyver]

... You don't need to buy one, just rent time on one...

At the speed that I learn, owning would be cheaper.