What causes timing to decrease as RPM's increase?

[DRASTIC.]

figured i'd post in here bout my srt-4 tuning issue due to the higher influx of activity...the tuning thing is a universal problem and not just pinpointed to 1 car, so i figure it works in here...tons of knowledgeable guys on here that frequent this section that could be able to help.

im having an issue here w/ my tuning... my timing is DEcreasing as my rpms go up, when it should be increasing..
what could be the resort of this?

just put in new coil, new wires, new 2step colder plugs, and a 250psi meth pump (upgraded from the 150),meth inj on straight 100% meth, 25psi. 6.8:1 compression (yep, way low!..srt heads flow like sh** even fully built w/ +1/+2 valves and 282/280 cams :/ )

timing starts out at 22* and stays there pretty consistently until right around 6k...then it plummets to 12-14* and stays there until 8k. knock was a low 0-1*

what would be the causes of this? i had this same issue w/ my last motor build but i thought it was because of the compression (8.5:1) and because i never balanced the motor...so i built this motor and did everything properly the way i should've the 1st time, but took extra percautions to prevent the timing issue to arise... (low compression custom dished pistons...no valve reliefs or sharp edges to prevent detonation, spherical-ized my combustion chambers, 250psi meth pump upgrade from the 150psi pump)

pretty stumped..
lowered my knock sensor sensitivity some due to my 282* cams making loud valve train noises, twin disc clutch clatter, and short skirt pistons all probably inducing some harmonic noises..helped with some phantom knock at WOT, but didnt really help my timing drop issue..

next step right now is a COP system i built, and a custom plug that doesnt sit as far into the combustion chamber and is 3steps colder. i know those are the culprit to my problems, but at this point anything helps.

i tried a quick google search as to why timing would reduce as rpms increased, but came up short of finding good information. hopefully you guys can help!


thanks for any help!


mike

[Appauldd]

Sounds like at your power level you may be out of the load cells on the tables. Might try re-scaling it.

It would help greatly to post a log of this condition occurring. Then we can take a look and determine if the tune is the cause and where.

[Dave W.]

Timing is controlled by the ecu. Which tuning system are you using?
I know on the 1990-1994 DSM the timing map at WOT has timing peak at 6k rpm then it drops. If the SRT4 has a similar 'feature' then you need to change the timing map.

[tkklemann]

Timing should decrease as the RPM increases, provided the load is increasing with the RPM as well. If your load is NOT increasing with the RPM, then you would have more of a problem then.

Arbitrary numbers here in this example:

At idle your car will say be idling at 5*, as you accelerate, the timing will go up to say 15-20* till say 2K, then it should uniformly start to decrease to peak torque to say 1-8*, then ramp up till redline to say 15-20*. (Remember, arbitrary numbers)

In the end, your timing should look like, when plotted out in a graph vs. RPM, a ramp down to peak torque, then ramp up to redline.

In your post, unless you aren't explaining something, or I am missing something, it sounds like your car is doing what it is suppose to be doing.

Try reading this thread here, specifically the Timing section. I think it has a pretty good explanation on how the timing works on a car. From what you posted it sounds like all is normal.

http://forums.evolutionm.net/ecuflas...-tune-evo.html

[DRASTIC.]

Timing should decrease as the RPM increases, provided the load is increasing with the RPM as well. If your load is NOT increasing with the RPM, then you would have more of a problem then.

Arbitrary numbers here in this example:

At idle your car will say be idling at 5*, as you accelerate, the timing will go up to say 15-20* till say 2K, then it should uniformly start to decrease to peak torque to say 1-8*, then ramp up till redline to say 15-20*. (Remember, arbitrary numbers)

In the end, your timing should look like, when plotted out in a graph vs. RPM, a ramp down to peak torque, then ramp up to redline.

In your post, unless you aren't explaining something, or I am missing something, it sounds like your car is doing what it is suppose to be doing.

Try reading this thread here, specifically the Timing section. I think it has a pretty good explanation on how the timing works on a car. From what you posted it sounds like all is normal.

http://forums.evolutionm.net/ecuflas...-tune-evo.html

sorry if i wasnt totally clear.
say im cruising at 3500rpms, and timing at cruise is 35*. ill go wot, and timing will drop down to 18-21* until peak tq. at that point, timing should trickle up to 25* or so..
but on my car, timing instead plummets to 12-14*. at that same instant, due to the higher egt's of low timing (for our car) afr's plummet due to a false rich down to 9.8-10.0afr..no knock.

im trying to figure out what the main cause of that would be, and how to fix/prevent it.




Dave W.:
i run a diablosport for our car...tuned via email logs of everything via by the creator of the DS software for the srt-4. i can then after receiving a new file flash, can move timing, fuel, boost (if pcm controlled still), rev limit and such around on my own.
i can surely post logs. you would need the free datalogging software from DS' website though.
http://diablosport.com/index.php?mod...=145#downloads

my tuner justsent me a new file to flash and see how it reacts today, but he never gave an answer as to what was going on..
ill datalog some pulls tonite and compare the 2 and see if there's any changes/improvements.

[Dave W.]

Could you watch the boost gauge? Perhaps boost is rising at high rpm (boost creep?), which would cause an increase in load and timing would drop.

[FunkyP]

Lots of safety features can come into play if your using them, ie: IAT related timing. If that not correctly set once you achieve a certain IAT the ECU will pull timing as it continues to rise.

....................
every 10deg F above 125deg F pull 2 deg Ign Timing <-- Something like that. If its set incorrectly that will cause a similar issue.


But yes, you dont want to run too low of timing otherwise the CC will get TOO hot.