For some reason this triggers a lot of guys on truck forums. They claim it's impossible and I can understand why. I don't know enough to know one way or the other, but I've tested 87 through 94 octane over 36k miles the 22 V6 ZR2 and can say without a doubt that higher octane (specifically 93-94) will eliminate the rough 2-1 downshift in the 8L45. The transmission, for reasons I can't explain, functions better overall on the higher-octane gas. I recently tried 94 because it's now available in NJ. It is not placebo. I've done back-to-back testing over hundreds of miles. The shifting and overall performance is better on 91> octane.
A guy on one of the FB groups explained it:
"The newer GM stuff uses torque tables to determine shifting. So it does get engine data to use for shifting."
"I will try to explain this as best I can - if or when I screw up others can chime in to correct me
To begin with - As best I can tell even on gen 4's the torque model is also used to control timing and throttle progressions under mostly light throttle conditions - haven't seen it effect wot conditions on a 4th gen as of yet - weird timing bites at cruise are a possible side effect from this working in conjunction with the throttle follower and idle tables / It's primarily used to control transmission line pressures - not only shift pressures, but heavily controls or rather influences the "hold" pressure, so the next time your "tuner" tells you that 6l90 or 6l80 just wasn't stout enough to handle that 650 or even 850 hp engine - keep this in mind - a lot of people don't touch this due to laziness and fear If you have a trans that shifts hard and firm, but slips cruising down the highway pulling a mountain for example - this is your problem...
To adjust - the tables are designated by spark values (the spark closest to where the engine is running at - will vary between a couple "I assume" if values are close to one another) - axis - left axis is cylinder airmass with one extra (0) or map pressure in (kpa) depending on which tables your looking at / horizontal or overhead axis is rpm / to change the axis for rpm you have to change the tables in the tune itself although I haven't ever messed with them / cylinder airmass and map can be changed via the max controls on the left (only set as high as the engine may see for refinement of the main tables)
I log delivered tq and dial the tables in to more in line with reality / 5th gens are supposed to have better ways of logging, but "I" have yet to get it to work
These will make a difference in "peppiness", drivability and longevity of components - only ever once saw power from them and pretty sure that was a fluke after someone else did more studying into the functionality of the OS's..."
Another individual:
"Lastly, the impact of 93 on the transmission:
I'm not sold on this, but i am willing to entertain the thought. Increasing the octane of the fuel will result in higher load if the computer is able to adjust for it, which as we discussed above is not likely. However, an automatic transmission is also calibrated on an RPM x load grid (most tables are), and if at the same conditions a higher octane allows for a higher load, it may be enough to move into a separate part of the shift table(s) where the computer / driver / both are more happy with how the vehicle is performing."
People need to go look at the native tcm program.
Yes there are engine perameters in the tcm that are torque based.
And those tables are populated based upon which octane map you are in.
There are 4 maps in the v6 Colorado. High octane, medium octane, low octane and limp
Well actually 5 if you include the “learned spark” and “learned fueling” map adjusters.
"You guys realize that your 3.6l Colorado has 11.5:1 compression right? They make regular "work" by retarding timing from ideal. That makes it possible to run regular to appeal to a larger market, but that doesn't make it ideal. This is evidenced by default timing advance being high and learning down to lower octane fuel and not vice-versa.
I'll stop trying to educate you guys and let you do what you want, but you are not running ideally on regular in the 3.6, and that's a fact.
For the record, these trucks aren't "regular recommended" they are "87 minimum." there's a difference."
A guy on one of the FB groups explained it:
"The newer GM stuff uses torque tables to determine shifting. So it does get engine data to use for shifting."
"I will try to explain this as best I can - if or when I screw up others can chime in to correct me
To begin with - As best I can tell even on gen 4's the torque model is also used to control timing and throttle progressions under mostly light throttle conditions - haven't seen it effect wot conditions on a 4th gen as of yet - weird timing bites at cruise are a possible side effect from this working in conjunction with the throttle follower and idle tables / It's primarily used to control transmission line pressures - not only shift pressures, but heavily controls or rather influences the "hold" pressure, so the next time your "tuner" tells you that 6l90 or 6l80 just wasn't stout enough to handle that 650 or even 850 hp engine - keep this in mind - a lot of people don't touch this due to laziness and fear If you have a trans that shifts hard and firm, but slips cruising down the highway pulling a mountain for example - this is your problem...
To adjust - the tables are designated by spark values (the spark closest to where the engine is running at - will vary between a couple "I assume" if values are close to one another) - axis - left axis is cylinder airmass with one extra (0) or map pressure in (kpa) depending on which tables your looking at / horizontal or overhead axis is rpm / to change the axis for rpm you have to change the tables in the tune itself although I haven't ever messed with them / cylinder airmass and map can be changed via the max controls on the left (only set as high as the engine may see for refinement of the main tables)
I log delivered tq and dial the tables in to more in line with reality / 5th gens are supposed to have better ways of logging, but "I" have yet to get it to work
These will make a difference in "peppiness", drivability and longevity of components - only ever once saw power from them and pretty sure that was a fluke after someone else did more studying into the functionality of the OS's..."
Another individual:
"Lastly, the impact of 93 on the transmission:
I'm not sold on this, but i am willing to entertain the thought. Increasing the octane of the fuel will result in higher load if the computer is able to adjust for it, which as we discussed above is not likely. However, an automatic transmission is also calibrated on an RPM x load grid (most tables are), and if at the same conditions a higher octane allows for a higher load, it may be enough to move into a separate part of the shift table(s) where the computer / driver / both are more happy with how the vehicle is performing."
People need to go look at the native tcm program.
Yes there are engine perameters in the tcm that are torque based.
And those tables are populated based upon which octane map you are in.
There are 4 maps in the v6 Colorado. High octane, medium octane, low octane and limp
Well actually 5 if you include the “learned spark” and “learned fueling” map adjusters.
"You guys realize that your 3.6l Colorado has 11.5:1 compression right? They make regular "work" by retarding timing from ideal. That makes it possible to run regular to appeal to a larger market, but that doesn't make it ideal. This is evidenced by default timing advance being high and learning down to lower octane fuel and not vice-versa.
I'll stop trying to educate you guys and let you do what you want, but you are not running ideally on regular in the 3.6, and that's a fact.
For the record, these trucks aren't "regular recommended" they are "87 minimum." there's a difference."
