Quote:
Originally Posted by Meph
Hey Guys,
Im working on tuning a project car of mine, It runs a standalone engine management system that requires you to edit all the variables about the engine.
I'm struggling to find some reliable data about Ignition Timing at 1500RPM under light load (-24 to -16 in-Hg). I know each engine is diffident and will run various numbers but any input will help, Ive seen people who programmed values as low as 16 Deg timing, and some as high as 38 deg.
I think scan gauge lets you monitor spark advance so if anyone can recall what their car runs at 1500 rpm + light loads it would really help out. Logically it would make sense that too much timing will reduce efficiency as it builds excess pressure during compression, even if not at the point of audible pining
Who says you cant have power and an efficent engine, 1973 datsun 240z w/ Toyota 2.5L 1jz-gte, really tall gears  300hp, 30 MPG goal
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"Light load" is the big DEPENDS in your question.
During normal driving it is often hard to actually hold a solid "steady" cruise at one load level. If you could, then as you said the optimum SA would depend on the engine combination and the conditions. The available torque of the engine in relation to the vehicle weight, drag, and final drive ratio will be major factors in determining the right timing for a given measured load or vacuum.
In general, a torquey engine coupled with a light vehicle and a lot of gear (more torque multiplication), will be able to effectively use more spark advance.
There are many other factors that weigh in on this requirement, such as: coolant temp, air temp, AFR, charge contamination (EGR), static and dynamic compression, camshaft timing, fuel octane, sparkplug type and heat range, etc...
Ultimately you will have to experiment. You should datalog and watch the output from your knock sensor. You can also watch a vacuum gauge and listen for audible spark-knock.
To give you a ballpark for a relatively low compression I6 with highway gearing your spark advance numbers would look something like this at around 1500 RPM:
Vac -- SA
05" -- 16* (heavy accel or PE mode)
10" -- 18* (heavy accel or PE mode)
12" -- 22*
14" -- 28* (light accel)
16" -- 34* (steady cruise @60 MPH ~1500 RPM I'm guessing)
18" -- 36* (light decel)
20" -- 38*
22" -- 40* (heavy decel or DFCO)
24" -- 40* (heavy decel or DFCO)
There is normally a pretty steep shift in SA between a steady cruise and light acceleration. If you're filling out cells in a spark advance table or map, then keep this in mind. The steep shift will show diagonally across your spark table as RPM increases.
If you are running with the turbo boost, then naturally you're going to see an even steeper drop in SA as manifold pressure is increased.
This steep shift throws off a lot of people calibrating their spark maps because it isn't a very smooth transition that they may be wanting to see.
Are you running a mechanical+vacuum advance distributor or a fully ECM controlled advance?
As an example of SA at a steady 60MPH cruise in my Ford Focus, the scangauge says 41*. Keep in mind this is assuming a heavy EGR operation that accounts for around 30% of the total VE value at that point in the calibration (30% dead air to slow the burn).
Without EGR the burn speed is higher, and the optimum SA is usually 5* to 10* lower for many engines.