Newbie Adaptive spark scaler help

[Wheelz]

I did a quick search and didnt really see much on this. Can someone point me in the right direction? From logging my truck it would appear that the adaptive spark scaler only drops with knock detection, but then it rebounds back when I'm cruising, which seems fine except it raises my spark back high enough to cause knock when the engine load increases again. To me the point of a high and low octane spark map is to run near the low octane map when I'm running 87 so I don't cause knock but still have the higher timing values available when I'm running 91 octane. Or are you just supposed to live with the sporadic knock when running low octane gas? Thanks in advance.

Ill post my tune and a log up tomorrow.

[ferocity02]

Here's my understanding, hopefully someone can correct me if I'm wrong. The PCM does not know if you're running 87 or 91. Instead, it runs on the high octane table all the time except when there is detonation, and then it uses a mixture of the high and low tables. The adaptive spark scalar determines how much of each table to use. I would tune it to run on 87 or 91 and stick with that fuel, no reason to be switching between the two. If you are getting knock you need to drop the timing, or the fuel mixture is off.

[joecar]

If you're running any LSx engine then you should be running 91 or higher.

[Wheelz]

If you're running any LSx engine then you should be running 91 or higher.

It's the truck in my signature. It's the HO 5.3 so is that still considered an LS based engine?


And I see your point about tuning it for a particular octane

[joecar]

Yep, the L33 is a GenIII.

[Wheelz]

Yep, the L33 is a GenIII.

Interesting... I guess Id better give up 87

Thanks.

[hog]

Speaking of octane, 1997 extended cab 2wd Vortec 350 L31 4l60e, 3.42 G80, I have been running North American 87 octane which is R+M/2(Reseach + Motor octane /2) for months. I then threw in 1/2 tank of 91 octance and noticed improved performance. I ran that down til the fuel pump pickup ran dry, then filled a 1/4 tank of 94 Octane Sunoco and was impressed to realize even furthur acceleration benefits. I cant quantify the gains, but they would be there for sure. This was with a stone stock GM calibration.

BTW The l31 runs the same 9.4:1 compression ratio the GEN3 4.8/5.3 engines run. The L33 runs a 9.9:1 CR though.

peace
Hog

[joecar]

If compression ratio is above 9, then higher octane is required to avoid detonation/preignition/knock...

L31 is GenI/SBC based, has lower CR, so it can get away with 87 or 89... but over time carbon deposits on the combustion chamber and piston tops causes the CR to increase slightly.

L33 is GenIII which typically has higher CR... it needs 93 (but California has limited this to 91).


With lower octane fuel, the PCM will hear knock and will command less ignition timing... when it stops hearing knock, it restores timing, only to hear knock again, and the cycle repeats.


If you find better performance with higher octane then this means the PCM is able to run the higher timing without hearing knock.

[Wheelz]

Thanks for the info. I'm in Texas so I just topped off with 93. Looking forward to seeing a difference