Ignition timing help (scan gauge)
 

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 :D 300hp, 30 MPG goal

http://carphotos.cardomain.com/ride_...0095_large.jpg

I'm running between 38-40 normally on flat to slightly hilly roads. Our motors are different though...
If you have a wideband, why not try leaning it out on the light load cruise, then you may get better mpg. I'm running mine around 17.5:1 and seeing some nice improvements.

"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.

On most engines, you can be well into the 35 - 45 degree range for SA before you start to lose efficiency.

I have some limited experience with stand alone units . The factory changes spark advance a lot in most cars some goes to 40 deg at low speed/ part throttle vacuums .
On after market though on many units if you try to do same things you can run into transit knock advance issues , its like the stand alone is not as fast ECU or not enough break points . Either way many don't go high on part throttle advance so transition to load is smoother. another way to think of it is pre ECU control , think of the vacuum advance unit on distributor and running with it off , thats another way to look at it .

See if you can add a knock sensor to the management system it would just go into one of the freeze plug locations. That way you will be able to see the knock and adjust from there.

My 03 GrandPrix I will see 50degrees in low loads cruising that is the ECU max but during that time EGR is running adding timing also I think that the spark table calls for a max of 42ish I would have to look at my tune.

Thats for all the input!!

My ECU dosn't have any knock sensor capability so I only have my eyes and eyes to detect any knock. Ive run as high as 32 deg before I started to question my luck and pulled it back to 30 for now (29 in my picture). The rest of my timing map is fine, its generally backed up by a lot of others out there for the 1jz, just the 1500 range is always all over the place, and as I spend a lot of time cursing at 1500 id like to get it right.

The 8:5 compression and 91 oct will slow down he burn, so I can few a couple more degrees on for that. My 1500 rpm is around 70 km/h if I recall correctly, maybe closer to 80, its not running 1500 at highway speeds but my county cruising range is right at 1500-2000. While not extremely tall, 2000 on the highway is a lot lower than then 3200 my last did.


http://img10.imageshack.us/img10/8954/74792739.jpg

I do have a wide band set up that lets me adjust the target A/F, right now I've set it for 15.3:1, and tuned my maps to around 14.7:1 and let the closed loop correct for it, are noticeable improvements found by leaning it out much more? 17.5:1 always seemed like a lean burn condition to me, will a stock engine take this kinda tune?

When you say you can be into the 35 to 45 range before losing efficiency are you talking specifically at 1500? At 1500 everything moving slower than usual so I know the timing wont be as far forward as 2000+

If anyone has some thoughts on my map, please let me know, and if it would be helpful to post the entire map Id definitely like to if someone can give me their input

How much timing are you running at idle and 1k rpm . How many maps are there between 1k and 2k (map ever 100, 200, 500 etc) rpm ?
Does This turbo engine have a EGR working , that will be a factor .
I think 35 deg at 1500-2000 "probably" be ok even without EGR operating but needs testing .

With out factory knock sensor you could use external knock sensor or microphone listening devise and ride around an test. Just make sure you pick warm day with engine warmed up good . Another way if your careful (no boost or loads) is to use 87 fuel and see when timing induces a lit ping at 1500. then back off a bit and use 91 .
Thats only if you really know what light ping sounds like and your exhaust/engine is quiet so you can hear good .

If you could please verify the units along your X-axis there.
PSI and inches of Hg are not the same thing.

edit: If you don't completely trust converting the figures, then just put a vacuum gauge on your manifold that reads in inches Hg, then compare to what your datalogging values are.

no EGR, JDM engine. I have a vac/boost gauge int he car and the values between my MAP sensor and boost gauge are comparable. The X axis is all in PSI, the conversion is somewhere around 2.03, I can talk in -psi or in-Hg, but not many people use -psi.

the incitements are in 500 rpm between maps with the ecu averaging the values in between. Someone is running 38 degrees apparently, so 35 seems reasonable, Ive run 32 before. Im not really experienced with detecting ping, ill ramp up slowly, eeping a keen ear open, I've installed multiple mufflers ont he car to reduce noise, its still loudn with a lot of road noise but i think I can still pick it out.

Thanks a lot for participating in the discussion everyone, ive posted the question on 4 different forums without a responce at all till now :D