low octane table and timing question
Feb 8, 2007 | 02:30 PM
#1
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From: Cleveland Mississippi
low octane table and timing question
Right now my timing is set at 25. We're taking a road trip to the track this weekend. My question is...If I put enough 87 octane in my truck to make the trip to the track, then put in 93 when I get there, how long does it take to for the pcm to start back adding timing based on the octane? What chance would it be that my pcm would even knock back on the timing running 25 degrees? Just trying to save a buck or two on the trip.
Feb 8, 2007 | 02:41 PM
#2
Originally Posted by slowprocess
Right now my timing is set at 25. We're taking a road trip to the track this weekend. My question is...If I put enough 87 octane in my truck to make the trip to the track, then put in 93 when I get there, how long does it take to for the pcm to start back adding timing based on the octane? What chance would it be that my pcm would even knock back on the timing running 25 degrees? Just trying to save a buck or two on the trip.
As far as 25* goes... It's not just your WOT knock that will affect your spark scaler. 25 may or may not knock at WOT. I've seen some trucks run fine at 25* on 87 octane without any knock, while others are knocking at less than that.
Looking at a 2004 4.8L tune, the conditions are: any knock greater than 2* that is detected above MAP of 50kPa between 300 and 6200rpms while in closed loop will alter the scaler.
Feb 8, 2007 | 04:54 PM
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From: Cleveland Mississippi
Originally Posted by dc_justin
The PCM is constantly altering the spark scaler (knock learn factor in HPT). It's impossible to say how long exactly it will take for it to full recover, but I would say if you fill up with 93 octane 20 miles or so before you get to the track, you should be sitting pretty good.
As far as 25* goes... It's not just your WOT knock that will affect your spark scaler. 25 may or may not knock at WOT. I've seen some trucks run fine at 25* on 87 octane without any knock, while others are knocking at less than that.
Looking at a 2004 4.8L tune, the conditions are: any knock greater than 2* that is detected above MAP of 50kPa between 300 and 6200rpms while in closed loop will alter the scaler.
As far as 25* goes... It's not just your WOT knock that will affect your spark scaler. 25 may or may not knock at WOT. I've seen some trucks run fine at 25* on 87 octane without any knock, while others are knocking at less than that.
Looking at a 2004 4.8L tune, the conditions are: any knock greater than 2* that is detected above MAP of 50kPa between 300 and 6200rpms while in closed loop will alter the scaler.
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