I was curious about my timing at 95 and 100 kpa. There seems to be quite a difference between 85, 90 kpa and 95 and 100kpa. Should my timing be higher or maybe a little smoother transition like I have heard the maf tables need to be. The car is an 11 psi 383 with methanol. I always assumed that the timing advance would increase with rpm up until redline.


85 90 95 100 kpa
25.5 25.0 15.5 15.0
26.5 26.0 16.5 16.0
29.0 28.5 17.0 16.5
30.0 29.5 19.0 18.5
31.0 30.5 20.0 19.5
32.0 31.5 21.0 20.5
33.5 33.0 20.5 20.0
35.0 34.5 26.0 25.5
35.5 35.0 30.5 30.0
36.0 35.5 30.0 30.0
37.0 36.5 31.0 31.0
38.0 37.5 34.0 31.0
39.0 38.5 33.0 31.0
40.0 39.0 32.0 31.0
40.0 39.0 32.0 31.0

37.0 35.0 29.0 29.0 4000rpm
37.0 35.0 29.0 29.0 4500
37.0 35.0 29.0 29.0 5000
37.0 35.0 28.0 28.0 5500
37.0 35.0 27.0 27.0 6000
37.0 36.0 27.0 27.0 6500
40.0 38.0 27.0 27.0 7000

 

Could it be because my a/f starts to go lean around 5000rpm???

Is it possible to be at 100kpa and 5000+ rpms and not be in WOT?

 

looks like a safe tune. with being boosted, 95-100 should be at boost.

 

Don't forget, The PCM typicaly adds about 3 or 4 more degrees at WOT over what the tables say.


Steve

 

with boost youre supposed to retard the timing as boost increases or else itll knock

 

21.0 21.0
21.0 21.0
22.0 21.0
23.0 22.0
24.0 23.0
25.0 24.0
30.0 30.0
32.0 32.0
32.0 31.5
32.0 31.0
31.5 30.0
30.5 29.5
28.0 27.5
28.0 27.5
28.0 27.5

thats mine, yours has alot more timing but its beccause of your meth im guessing

 

I've never heard that

 

Do a dyno pull and log data with Datamaster and if you have 27 degrees in the spark advance vs rpm table at 6000, Datamaster will show around 30 to 31 degrees on the log. Datamaster reports the real number. The GM PCM has a hard coded adder in somewhere. As rpm goes up the adder goes up. I've seen it on every LT1 I've done. I have confirmed that Datamaster reads true timing on my 94. I installed a crank pointer at TDC and verified Datamaster timing matches true timing with a dial back timing light. Strange but true.

Steve

 

INteresting...thanks for the info

 

Its been speculated that the elusive 3deg of advance is tied to the inlet air temp.... hence the small performance gain on some cars when you use the resistor in the IAT sensor harness, or relocate the IAT sensor to eliminate heat soak.

Just to clarify... DataMaster or any other scanner simply reports the timing advance that the PCM is calling for, not the "real" number or the "true" timing. The value that the PCM calls for is made up of the value from the tables, any "offsets" hidden in the program, and knock retard. There is no feedback to the PCM to verify the "actual" timing the ignition system is providing, but logically, they should be the same, unless you had an oddball situation where the Opti was indexed incorrectly.

 

Agreed, There's no feedback loop to the PCM to moniter true ignition timing. My verification came in the form of a good old fashioned dialback timing light that compared favorably with Datamaster "Commanded Timing"

Steve