LS1s and tuning

[kevm14]

The video is entitled "LS1 Tuning Explained - Why do they gain so much from tuning?" which caught my eye.

https://www.youtube.com/watch?v=VfpmNhCKBis

Watching now.

[Adam]

How do the newer PCMs compare to the older ones as far as timing tables go? Do the LT1 have separate low and high octane timing maps or do they just pull X degrees of timing from the standard map under knock?

[kevm14]

LT1s have high and low octane tables. There is some knock retard learning but it is pretty crude compared to the newer stuff.

I believe the newer cars are able to dynamically arrive at a hybrid table between the two (low and high) based on KR activity (and likely other parameters).

My Caprice, however, with its ancient-even-by-1993-standards ECM, is about as unsophisticated as you state. More specifically, it allows a max retard based on a simple table, and will pull up to that much while there is still knock activity. No learning at all. Some parameters are available such as the rate at which spark is pulled, and given back.

[Adam]

Also interesting information about MAF vs. MAP tuning.

[kevm14]

Here are the tables for my CTS-V, which uses an older LS1 generation PCM.

CTS-V spark advance.PNG

CTS-V spark retard.PNG

CTS-V spark dwell.PNG

CTS-V spark knock sensors.PNG

Here is the knock sensitivity vs RPM vs cylinder table. Apparently GM thought cylinders 2 and 5 needed to have a slightly lower sensitivity to knock, and will allow more knock before doing anything in those cylinders, above like 4,400 rpm.

CTS-V spark knock sensors knock sens vs RPM vs cyl.PNG

[kevm14]

Also interesting information about MAF vs. MAP tuning.

For basically any kind of hopped up LS-derived build, everyone likes the aftermarket 2 and 3 bar speed density OSs (HP Tuners has some, for example). They run really well. Turns out speed density works well with high resolution sensors and enough computing power to actually do real time calculations.

[Adam]

US units! Finally, I can understand the numbers.

[Adam]

Also interesting information about MAF vs. MAP tuning.

For basically any kind of hopped up LS-derived build, everyone likes the aftermarket 2 and 3 bar speed density OSs (HP Tuners has some, for example). They run really well. Turns out speed density works well with high resolution sensors and enough computing power to actually do real time calculations.

Makes sense. Being able to measure engine load more directly (MAP) is more accurate than inferring it (MAF + TPS + RPM + ...). You can spend your computing time doing more useful stuff.

[kevm14]

Obviously I can pull up any table you want.

However, it's more fun (and I encouraged Bill to do so) to download the demo HP Tuners VCM Editor and get some stock PCM calibrations to look at. I think one of my favorite tables from my CTS-V is the "anti piston slap" table, which heavily manipulates spark advance during certain warmup/load situations.

CTS-V spark advance piston slap.PNG

It doesn't seem to have a temp parameter so I don't know if this is really all the time or what. But I can tell you that's light load.

I think the theory is the crazy extra spark advance lights off the mixture so early that it helps maintain pressure on the piston to keep it from rattling. No idea if that's accurate or not. I don't hear any and I've never seen an actual reliability issue from piston slap on LS engines so it doesn't concern me. This is a customer satisfaction table, plain and simple.

[kevm14]

Also interesting information about MAF vs. MAP tuning.

For basically any kind of hopped up LS-derived build, everyone likes the aftermarket 2 and 3 bar speed density OSs (HP Tuners has some, for example). They run really well. Turns out speed density works well with high resolution sensors and enough computing power to actually do real time calculations.

Makes sense. Being able to measure engine load more directly (MAP) is more accurate than inferring it (MAF + TPS + RPM + ...). You can spend your computing time doing more useful stuff.

I think part of it is the tune comes out better, especially on wild builds, because spark works better tied to engine load rather than airflow. Someone out there probably explains it well.

And the fact is, trying to stick with MAF on more hot rodded builds just adds unnecessary expense (upgraded MAF) and still ends up being a restriction in the air intake.