LT1 Commanded Timing vs Datalog don't match
05-26-2006, 12:06 PM
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Car: 1992 Chevrolet Corvette
Engine: LT1
Transmission: ZF-6
LT1 Commanded Timing vs Datalog don't match
A friend of mine is running a speed density LT1 setup that he has recently added heads and a cam to and I was trying to help him get it tuned out. A few minor driveability tweaks aside it seems to be doing pretty well. In doing some dataloging though I noticed that something wasn't quite right with the timing.
I'm using Datamaster DA and TunerCAT to work on the tune. My attention was first brought to an area of a data log where the car encountered a little bit of spark retard. I zoomed in on the area and was going to see about playing with the timing in that area. What I noticed immediately though was that the timing value in the computer is NOT the timing value in the data log.
For example at a particular point in the data log the car is obtaining zero timing retard, MPA is 100.8 KPA, RPM is 3700 and it is showing a spark advance of 33 degrees. When I open up tunercat though i see that for a MAP value of 100 and an RPM 0f 3600, the commanded timing value is 36 degrees. Likewise at 4000 RPM's the commanded value is 36 degrees. Logic would tend to state that for 3700 the computer would be forced to interpolate between 3600 and 4000, both of which being 36 should return a value of 36.
I started looking at other places and sure enough, at any random point in his data log I can find that the spark advance is showing 3 degrees less than the commanded value. I've looked all over the computer and I can't really find any reason for this to happen. The only thing I can really see is the "low octane" spark retard, but I have no idea when the computer references this table. If it is referencing this table, is there supposed to be some kind of a flag in the data log that would tell me? Short of zeroing the low octane table and seeing if it makes a difference, is there any way to tell?
Then I got to thinking, maybe I'm chasing my tail. If the spark advance reported by datamaster is an ACTUAL spark advance instead of a commanded value, then maybe there might be some physical problem? Would this even be possible with the optispark? Could it somehow be "skewed" and running an incorrect timing, or at least be reporting an incorrect timing?
Honestly I don't know where to start looking. We were hoping to dyno tune the car before long but I don't really know what to do with it. If it's consistently running 3 degrees shy of the commanded value I suppose I could add 3 to all of the tables, but then what happens if it magically starts running like it's supposed to?
The car seems to run just fine but I don't understand what is going on. I would really like for the car to do what the computer is commanding it to before I try to do any dyno tuning for WOT.
Any thoughts or suggestions would be greatly apprecitated!
I'm using Datamaster DA and TunerCAT to work on the tune. My attention was first brought to an area of a data log where the car encountered a little bit of spark retard. I zoomed in on the area and was going to see about playing with the timing in that area. What I noticed immediately though was that the timing value in the computer is NOT the timing value in the data log.
For example at a particular point in the data log the car is obtaining zero timing retard, MPA is 100.8 KPA, RPM is 3700 and it is showing a spark advance of 33 degrees. When I open up tunercat though i see that for a MAP value of 100 and an RPM 0f 3600, the commanded timing value is 36 degrees. Likewise at 4000 RPM's the commanded value is 36 degrees. Logic would tend to state that for 3700 the computer would be forced to interpolate between 3600 and 4000, both of which being 36 should return a value of 36.
I started looking at other places and sure enough, at any random point in his data log I can find that the spark advance is showing 3 degrees less than the commanded value. I've looked all over the computer and I can't really find any reason for this to happen. The only thing I can really see is the "low octane" spark retard, but I have no idea when the computer references this table. If it is referencing this table, is there supposed to be some kind of a flag in the data log that would tell me? Short of zeroing the low octane table and seeing if it makes a difference, is there any way to tell?
Then I got to thinking, maybe I'm chasing my tail. If the spark advance reported by datamaster is an ACTUAL spark advance instead of a commanded value, then maybe there might be some physical problem? Would this even be possible with the optispark? Could it somehow be "skewed" and running an incorrect timing, or at least be reporting an incorrect timing?
Honestly I don't know where to start looking. We were hoping to dyno tune the car before long but I don't really know what to do with it. If it's consistently running 3 degrees shy of the commanded value I suppose I could add 3 to all of the tables, but then what happens if it magically starts running like it's supposed to?
The car seems to run just fine but I don't understand what is going on. I would really like for the car to do what the computer is commanding it to before I try to do any dyno tuning for WOT.
Any thoughts or suggestions would be greatly apprecitated!
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