Reduce Timing How Many Degrees after it Starts to Ping?

[Yo J]

I have a TMax (Been very happy) so now I am tweaking timing...

Q:  How many degrees should I take out / reduce after it starts to ping?

Example... I can get slight ping with 36* do I go to 35*?, 34*?

I guess after reading this as I type, the question should be - How can you find the "sweet" timing spot?

Everyone Have a Safe 4th and remember our troops - Especially the Marines this weekend.

[Rider57]

I would take out 4*, run it and see if it's gone. If it is, add 1 back and keep adding 1 back until it reappears. then take 1 out again. I did it across the board. Worked for me.

[05FLHTC]

Take a couple of degrees out, then the next time you fill up, try the mid grade to simulate what's gonna happen if you are out somewhere & that's all that can be had...the other thing I watch is my oil temp, if it starts running significantly hotter you have gone to far. This method may leave a couple HP on the table but it's nice to know what octane your tune will run with before you have to find out the hard way. 

[-SeabrookTrickBagger]

Another way to look at finding the sweet spot for ignition timing ..........

The idea with performance ignition timing (excluding low rpm and/or low load situations) is to accomplish maximum cylinder pressure a few degrees (maybe 2-4 minimum and 10 to 12 is reportedly acceptable) AFTER top dead center which means you have to start the ignition process "at the right time" before TDC.  I know of no measurement you can readily do to find this magic few degrees ATDC. But, what I have found, quite clearly, is that if the ignition timing is too advanced at higher rpms and higher loads, you can retard the timing significantly and actually feel the engine spin very freely because maximum cylinder pressure is pushing the piston down after it passes TDC as opposed to pushing the piston down as it approaches TDC which is the upward stroke as opposed to the downward stroke. 

So, while too much advance may not in some instances induce ping, too much can still rob power from the engine and stress the engine internals.  I think this concept is much more important to grasp than finding maximum timing in relation to ping issues. 

Additionally, starting your ignition spark very early in order to achieve maximum output of the engine is comparatively very hard on crank and connecting rod bearings since both will feel the added pressure of the totally ignited fuel if the maximum cylinder pressure is achieved before TDC or at TDC at higher rpms.  For racing engines, this additional wear is not much of a concern.  Also, remember that some "ping" is silent, and it can usually be found by looking at the spark plugs for metal transfer from the piston to the spark plug. 

As for me, I look for engine temp reduction (idle, midrange and cruising rpms), a free spinning engine (high rpms) and power gains across the rpm range which I find by trial and, hopefully not much error.

Finally, keep in mind that as your afr changes, your timing needs change in that a richer mixture has a faster burn rate than a leaner mixture, generally.  Hence, you need less advance for a richer mixture such as 13.3 afr at WOT than you would at a cruising AFR of 13.8 since you can start the burn at a later time with a richer mixture (since it has a faster burn rate) and get your maximum cylinder pressure at, say 5 to 10 degrees ATDC.  Since high octane gasoline has a slower burn rate than midgrade gasoline, then engine will tolerate more advance with higher octane gasoline than lower octane gasoline.

[Steve Cole]

Most HD engines will begin to ping long before they are over advanced on today's pump fuels. About the only area you can over advance them is at low RPM and very low loads. Much anything over 2500 RPM and 50 kPa manifold pressure will ping if it's over advanced. As octane goes higher the burn rate is slower so you need to advance the timing to get the burn right. That's a big myth in that just adding high octane fuel makes it run better! If your engine was properly tuned on low octane fuel you will gain little to nothing by adding high octane fuel. Now on the other hand if you tune for the high octane most engines will pickup power and mileage.

[Ardy]

By Steve Cole: "Now on the other hand if you tune for the high octane most engines will pickup power and mileage."

My question is how much power and mileage? I had my 01 Ultra dynoed with premium 91 octane, GD Crane 310-2 cams and in the hot summer when my choice for fuel was 87 or ethanol 89 it sounded like a hail storm when I rolled on the throttle! I'm not looking for more power for the 08 Ultra but mileage is important. How much will I lose, power and mileage wise, tuning with the 87 non-ethanol gas? BTW, A/C and pipes now butI'm looking to install 255 cams and when I decide on which headers, stock or 2-2, I will be doing the work and finding a tuner. I figure CR with the 255's will increase into the 9.1 to 9.2 range.

[Steve Cole]

As a general rule of thumbe your going to lose about 5-10% going from 92 octane and a proper tune to 87 octane and a proper tune.

[EL-AL]

I don't understand.....
All twin cams call for premium, so why chance running 87 or 89 octane, except in an emergency?

[Yo J]

taking out 2* after first sign of slight ping seems to be the sweet spot