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Curious about knock retard- GM 3800 #4484652
08/10/17 11:19 AM
08/10/17 11:19 AM
Joined: Oct 2015
Posts: 449
MN
TmanP Offline OP
TmanP  Offline OP
Joined: Oct 2015
Posts: 449
MN
I went for a drive with an OBD scanner app this morning. I was curious to find out what my knock retard % was.
I'd say 80-90% of the time, it was 0 degrees. Under medium-light acceleration, it read about 2-3 degrees. Under moderate acceleration, it read about 4-5 degrees. I did two near-WOT runs and saw that it read in the 3-6 degrees range with a brief spike to 7-8 degrees (at about 5000 RPM). From what I've read, the 3800 tends to increase timing in some areas, necessitating knock retard sometimes. (Again, from what I've read, the naturally aspirated Series 3 3800 [L22] has the most timing advance of all). It seems to be quite normal, but I'm curious whether anyone who knows the 3800 can confirm this. The owners' manual says to use an octane of 87 or higher, and I've used primarily 87 E10. Premium (91) is 30-50 cents more expensive (30 cents is 91 with ethanol, 50 cents is 91 without ethanol or 93 with ethanol). Any thoughts?


2012 Toyota Camry 2.5 30,000 mi
2015 Chevy Silverado LT Z71 5.3 V8 30,000 mi
2010 Toyota Sienna 3.5 V6 150,000 mi
Re: Curious about knock retard- GM 3800 [Re: TmanP] #4484674
08/10/17 11:37 AM
08/10/17 11:37 AM
Joined: Oct 2009
Posts: 3,947
Ohio
L_Sludger Offline
L_Sludger  Offline
Joined: Oct 2009
Posts: 3,947
Ohio
Why don't you try higher octane and check the WOT retardation then? You have a test setup just begging for experimentation.


too many cars and oil combinations to list in 150 characters or less
Re: Curious about knock retard- GM 3800 [Re: TmanP] #4484681
08/10/17 11:46 AM
08/10/17 11:46 AM
Joined: Nov 2006
Posts: 20,787
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 20,787
MA, Mittelfranken.de
It can run on 87 but it will pull timing, I use 91 or 93 in them, the fuel economy seems to improve slightly also partially offsetting the price difference.


ASE L1, Master. Deutsch Meisterbrief.
Re: Curious about knock retard- GM 3800 [Re: TmanP] #4484709
08/10/17 12:11 PM
08/10/17 12:11 PM
Joined: Oct 2015
Posts: 449
MN
TmanP Offline OP
TmanP  Offline OP
Joined: Oct 2015
Posts: 449
MN
It is Naturally Aspirated- NOT supercharged. Does that make a difference??


2012 Toyota Camry 2.5 30,000 mi
2015 Chevy Silverado LT Z71 5.3 V8 30,000 mi
2010 Toyota Sienna 3.5 V6 150,000 mi
Re: Curious about knock retard- GM 3800 [Re: TmanP] #4484795
08/10/17 01:11 PM
08/10/17 01:11 PM
Joined: Nov 2003
Posts: 1,233
Middle of Iowa
DriveHard Offline
DriveHard  Offline
Joined: Nov 2003
Posts: 1,233
Middle of Iowa
Originally Posted By: TmanP
It is Naturally Aspirated- NOT supercharged. Does that make a difference??


Not really...GM pushes the timing for maximum efficiency and power. Run a couple tanks of premium and I bet you see that retard go to zero under almost all conditions. My high compression engine truck pulls timing even with premium. The only time it won't pull timing is when I run E85.


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