There are many things that can affect timing, poor fuel quality, combustion temps, etc. You have to realize also that back-to-back runs heat up the combustion chamber a lot and where a car was running fine on a certain type of fuel and tune in the beginning, it could later be susceptible to ping/knock once conditions in the block/heads heat up.
Also you can have changes in intake air temp that can be just enough to put the intake charge a bit too hot and more susceptible.
The maximum stock advance is 32-36 degrees. (at redline)
Even a "hard core" tune will not push more then maybe 45 degrees.
A typical pump gas tune is ~40 degrees maximum.
You can "actually" run more timing but it's only hurting your cause above that point.
at 100 F IAT you would NOT be adding timing. 100 F is dead on the Zero point for IAT timing changing as is 200 F for ECT.
Another thing to look at is the timing will never ramp higher then the LOWEST of the base timing tables. (plus IMRC adder of course) Well I guess except in very cold weather where the IAT and even ECT adds timing to promote more efficient fuel burn. The lowest of the 4 stock tables is 21 degrees advance at 6750rpm. The base table is 26 degrees. The IMRC adder is 10 degrees.
The "lowest" table is the borderline detonation table. This table comes into play if you run lower then the best octane premium and/or have detonation during a normal driving cycle. Some people say they can't feel a power loss running "regular" but the timing loss is huge so their butt dyno is off by a mile. PERIOD. (it's 5-15 degrees of timing pull all the time! )
This type of thinking rules the tuner world. They try to do timing changes without datalogging if any changes are really happening. MOST of the time they are not changing the timing at all or very little if they are because they forget a table or 3 or had timing changers pulling out significant timing. Tuning without datalogging is only doing half the job.
Oh you can command more timing in the PCM but it NEVER actually happens. Tuning without datalogging is pretty worthless!!!
There is a couple other issues as well
Also you should do some datalogging. You may be quite surprised to see what the timing actually is verses what it is suppose to be.
You can not just change the timing tables and expect it to work right
The SCT advantage software has all the tables in it and it has extensive dialogue that tells you how the spark is added/subtracted to the base spark and under what conditions. It is pretty good because it tries to explain how all the parameters interact so you can make good decisions on your tune. With a little practice you can sit down and calculate what your spark should be for any scenario by reading the table values at appropriate points
Here is the math from my spark tables with the best possible conditions:
Max possible spark
Highest base spark -- 41 degrees above 6100 rpm
ECT spark add/subt -- (100x0.015)=1.5 deg added for cold temps
ACT sparl add/subt -- (100x00.03)=3 deg added for cold intake temps
Spark added when going commanded open loop -- 3 degrees
IMRC adder above 6100 rpm -- 10 degrees
Total is 58.5 degrees
Of course this is max possible spark from my factory base tune under light load conditions (NOT Decel, decel is actually higher)
But, it isn't likely to be that high so, Here's the realistic one:
At .89 load;
base spark -- 26 deg
ECT add/sub (normal temps 200F-75F; factor 0 to 20 degrees , I'll go with 8 for this example) up to 8 x .05 -- .4 deg
ACT add/sub (cool intake air of 55F) = 55 x .05 -- 2.75 deg
Spark added whend going commanded open loop -- 3 deg
IMRC above 6100 -- 11 deg
Total spark at full throttle -- 43.2 degrees
Adding a larger TB:
Tuning your A/F is unnecessary just because you add a larger or smaller TB. It doesn't make your car leaner or richer.
The MAF is what reads the airflow. If airflow increases then the computer adds more fuel. Period. A larger TB is not going to change that. It may allow more air in the engine at WOT and high rpm but NOTHING that is outside the MAF's range. The only time you have an issue is if the airflow is out of the range that the maf is capable of reading. Though using the stock MAF is a good choice for the power levels any NA engine is capable of.
As long as you have retained your secondaries then running a large TB is not a problem. I ran a 70mm TB on my NA 3L and it worked pretty well. In actuality it made little difference in power above the 60mm TB. Now for a turbo it is a good idea on my car.
Now the reason we use an SAFC to tune with is to adjust what the COMPUTER THINKS that the optimum AF ratio should be to what YOU THINK the optimum AF ratio should be. On the SVT's the computer tunes for about 12.5 :1 in the midrange and then as rich as 11.8:1 on some cars at or near redline.
We have found through many tests that 13:1 gives great power on a naturally aspirated SVT. Even 13.5:1 will net you a few more horsepower but as the rpms approach 6000+ you will want to richen it back up to around 12.75-13:1 so that it doesn't ping under hot weather conditions.
That is the only reason we use an SAFC.
Tuning with the MAF function is absolutely the worst way you can do it. It's no better then hack tuning with a MAF voltage device. (i.e. screws up the load calculations!)
The MAF function should be a direct function based off the MAF electronics and the intake/setup. All your fuel tuning should be done with the fuel tables.
What does the PCM use as a basis to calculate load? It uses the corresponding KG/HR correlation to the supplied MAF Voltage. IF YOU ALTER THE MAF FUNCTION IN THE CODE IT WILL THINK IT IS GETTING MORE AIR THEN IT ACTUALLY IS. That means an inflated load reading. EVERYTHING is calculated using load.
You can not seriously alter the PCM's MAF function (verses the meter's electronics) without seriously corrupting the load calculations. PERIOD.
This is a plain and simple idea to understand.
There is a huge difference between minute changes to fine tune the MAF function to the intake and stupidly tuning WOT fuel trim with it.
Tuning with the MAF function is IMO a cut rate hack job to make a quick & dirty tune. (i.e. it saves their time) It is not an overly stable tune nor an ideal one in the least.
My fuel tables are 12.5-13.3 at WOT and my AFR is ~13 to 1. My PCM MAF function is within 3% of the electronics. The only changes were some fine tuning in the low rpm/low voltage range. Though you must realize that my setup is far from the stock intake setup. That is a properly tuned setup.
IF you set your lambda to 1 and you don't get a corresponding fuel ratio of close to 14.7:1, then your MAF transfer function is obviously not accurately reflecting the the MAF and the airflow.
The MAF is just a sensor to measure airflow. If you enter in the correct function, then the the base table will be the only proper way to tune. The PCM will know the amount of air and add the correct amount of fuel to hit the target lambda.
In reality, the MAF transfer functions aren't all that close sometimes and you need to tune with the function to get the maf to read the correct amount of airflow as possible. THEN you again tune with the base tables until you achieve the desired A/F ratio.
With small adjustments there is no problem adjusting the MAF transfer function.
I am talking about the actual fuel base tables. The basis for all fuel calculations for all times under closed loop. (there is also a separate open loop table) However these tables work the best and are the ones that should be used for making a properly designed program.
Creating a base tune:
the max allowed table is kind of the central table that all the spark timing hovers around.
All of the other tables (except for a one or two) are used in conjunction with the max allowed table. ACT and ECT tables are just multipliers of the max allowed spark value in a particular cell.
So if at 0.50 load and 3000 rpm you have a value of about 20* max allowed advance, the ACT at loads similar to that may introduce an 10% increase in spark at that point based on cool temps, or th ECT may also do the same. Then there is the IMRC which will add more spark at certain loads above the opening point. It ALSO works in conjuction with the max spark allowed table as a base table.
When I was planning out my Max allowed table, I started with stock, increased the load range on the Axes since I was forced induction to about .99 and then put limitations that I felt would be safe in the loads above 0.6 to 0.7 Then I let the computer actually add any timing to those maximum values based on ACT ECT and as long as it didn't go above my maximum desired timing. For example, I didin't want to go above 23* on a cool day boosting 7-8psi, so I did a rough calculation on the timing advance for cells above 0.85 at the appropriate RPM to determine the maximum it could hit, then adjusted the max allowed table accordingly.
As far as the MBT spark tables, they do absolutely NOTHING for advance but after I worked out the timing tables to my liking I adjusted them downward by about the same percentages to keep the computers torque calculations in-line.
Most importantly, I used a OBD II scanner, AND The XCAL2 to datalog while driving around to see what the values and loads were at cruise, idle, and full throttle. After about 5 days I had a good tune and felt comfortable to raise the boost after confirming with the wideband that the AFR was as expected.
Don't rely on the knock sensor tables to appropriately pull back timing as protection. They don't work all that good and you will be losing power in some cases before you actually experience predetonation.
Leave the stock settings mostly alone until you get it driving fine with no codes, doing only what is necessary to correct for intake system changes and other mods. Then change only one major variable at a time, such as increasing the maximum timing at max load, all by 10%, or changing only the last 1000 rpm by some amount. Address specific problems first. Have an overall plan of attack on what you want out of your car.or change the priority order once you know what you want.
I have found that a timing change of just 2* made the difference between a rough sounding engine at high rpm windout to a smooth sounding engine. I mean at 6000 rpm and spinning toward 7000 rpm, you can hear little things that are hard to describe. If you go slowly and increase till you get these audible changes, then pull back a little, you can get a 90% solution before you ever hit the dyno.
You can see, I was able to roll into the dyno in Montgomery and with NO required tuning changes after the first run. I was able to raise the power to the wheels from about 310 up to 355 in 3 or 4 dyno runs just by turning up the boost....at least until the soft wastegate spring began opening on its own. This is the power of the EEC-V adjustable PCM, getting the settings basically right and letting the computer adjust as it needs to, to meet those settings.