Timing curve & AFR for 8.1L Vortec

[christopherstone]

I have looked and looked and looked but cannot seem to find much info on this?

Does anyone with ACTUAL experience know what kind of timing curve these RATS like?

When tuning all my LSXs I would run 22+ degrees, sometimes up to 28*, as long as I wasnt seeing any decrease in power or any knock retard. This isnt an LS1/LS2/LS3, so I am kind of out of my element here.

What about AFR curve? I used to richen up just a little at peak torque, so if I was running, say 13 AFR flat across all RPMS, I would set it to be richer at like 4500 RPM, by a small amount. Like 12.75 or so. Then smooth that in. BUT! BUT: this engine makes peak torque wayyyy down low, so I am wondering if I should follow the same principal, richen it up a tad down low, and lean it out up top slightly? Right now it is set to 12.76 AFR across the board until I get the timing thing worked out.


Back to the spark: I noticed that I did have to tweak a few modifier/adder/correction tables to even get the 15* from the stock timing advance tables....I was just looking at my last log, and I had a momentary dip down to 9* at WOT @3000 RPM..? Im digging around trying to figure out why. ECT wasnt high, IAT wasnt really high. I have YET to see any KR logged in any of my 15 or so runs.

The IAT Spark Advance Correction table is set to pull quite a bit of timing with IATs relatively low, so I got rid of most of the IAT Correction below 130* IAT temps. That seems to allow me to get the timing I wanted to command at the Main Spark Advance table. The ECT Spark Advance Correction table is set to pull 1-2* when it hits 212-221*..I left those alone(Im usually around 19x* ECT) and will opt for a lower temperature thermostat (180* probably)to keep it from hitting those cells for sure. Hopefully it will bring down my IATs a tad as well. I will be installing that thermostat later on today after I finish putting the rear end back together lol...been waiting for my shiny new rear diff. cover & gasket to come in.

In the future, I do plan on moving the air intake/filter etc in an attempt to lower IATs. I will likely get with something NOT metal so it will help insulate the heat from the incoming air.

So what say you?

#1 what timing curves have you have experience with?
#2 did you have to change anything else to realize the full timing in the High/Low octane tables?
#3 how did you set up your PE EQ Ratio table?

Thanks guys. I am open to criticism!

attached is my base tune, set up for Open Loop/SD until I dial in the VE and timing all the way.

2001 Silverado 2500 HD 8.1L - Stage 4 Tune - SD Tuning Mode Setup - 12th.hpt

[Area47]

the most i have gotten out of them is 21 on the stock cam. and that seems to be the sweet spot for them with no load on 91 octane. toe in afr/peak torque 12.0 leaning out to 12.5 at peak hp. below 120 iat zeroed out, below 220 on ect zeroed.

[christopherstone]

Thanks btw

[christopherstone]

the most i have gotten out of them is 21 on the stock cam. and that seems to be the sweet spot for them with no load on 91 octane. toe in afr/peak torque 12.0 leaning out to 12.5 at peak hp. below 120 iat zeroed out, below 220 on ect zeroed.

Awesome. Glad i was on the right track. I zerod out under 131* iat, and ECT 203 and lower zerod.

12.0 is really rich! Thats odd! Ill try it though!

[Area47]

not for peak torque it's not. This is where the dyno comes into play to see what the engine itself wants. I tend to be conservative on tuning the bog trucks due to the towing loads that could be put behind them.

[christopherstone]

Cool, yea i dont have a dyno and i dont live where there is one.

If i tow ill be having a whole different tune for that. There is a product called in nGuage that is supposed to have support for GM vehicle soon. It allows you to switch between hptuners tunes on the Fly. Pretty cool. Until then I'll just be flashing it the old-fashioned way with the laptop.

If it was somebody else's truck, I would agree that I wouldn't lean it out anywhere near as much as it is. But it's my truck :-) its nice to try different things and learn from experience.

Maybe someday I can take a trip to a dyno :/

[christopherstone]

OK so I had to make some small changes to my PE EQ Ratio table:

PE EQ SCRN.jpg

[christopherstone]

I richened it up after redline since I dont plan on hitting those anyways

[christopherstone]

Just an update for any future readers out there... I finally was able to figure out that Burst Knock comes on too easy on these trucks..probably due to the fact that they do tow really heavy loads etc...and werent really meant for going fast.

Go into Engine / Spark / Retard / Burst Knock Retard / and click on Enable Delta Cyl Air. This table pulls timing in ANTICIPATION of knock, whether or not it would actually occur. A LOT of people just max out this table, disable the feature, and are done with it (The factory has it set to pull 5* when the value in the cells is exceeded from frame-to-frame)

I might need it later so I decided to just log Burst Knock, and in the areas I am getting 5* pulled I started just doubling the #s until I no longer saw ANY Burst Knock on my logs. Factory had it set to 0.020 grams. I had to keep adding .020 at a time and am at 0.140 in most cells except in the lower RPM areas ...I had to keep going and am at .160/.150 at 1600/2000 RPM. This has gotten rid of almost all of it. This is where I am at now for those that want something to copy and paste:

BurstKnockEnableDeltaCylAirThreshhold.jpg

[christopherstone]

Here is my High Octane Table:

MainSpark-HighOctaner.jpg

At low RPM/High Load (as in from a dead stop, you mashed it to WOT) I was seeing hardly any advance at all....

There was a huge hole in the factory table at that spot so I filled it in and got rid of some of the negative advance.

I was logging about 0.8g on launch, so I took a look at those cells.

If you compare the cells you hit when you got WOT from a dead stop ...you can see why it wont burn the tires.

Attachment 68161

[christopherstone]

So instead of 2, 6, 10, 12, 14 , 16 degrees...you get :

13 ,13 ,14, 16, 17, 18

It made a huge difference from a dig. Now I have to be careful so as to not roast the tires on launch. Im still tweaking it more as I go along, little by little. But this is definitely an improvement.

My wideband apparently decided to crap out on me..even though its only been used once lol. But whatever..I sent it into Innovate. Hopefully it doesnt take any longer than the two week max they said. I have been dying to get the AFR dialed in. I had to scrap me last VE because I had not notice the LM2 wideband wasnt giving out the proper output voltage...so I ended up with a trashed VE because I took too long to notice it was off. Ill post up my results then. In the meantime I guess I research how to tune using fuel trims...never done that before..I always have had a wideband.

[Matt_lq4]

not for peak torque it's not. This is where the dyno comes into play to see what the engine itself wants. I tend to be conservative on tuning the bog trucks due to the towing loads that could be put behind them.

Yessir, I can vouche for this even though my motor is a 6.0 lq4 instead of an 8.1. On the dyno I found the best torque and horsepower combo by richening to 12.0 before and at peak torque (4650 rpm in my case) and leaning out to 12.5-12.7 5000 rpm till redline. I gained up to 40 rwhp and torque in some areas especially at 4000 rpm

[Obsolete489]

Yessir, I can vouche for this even though my motor is a 6.0 lq4 instead of an 8.1. On the dyno I found the best torque and horsepower combo by richening to 12.0 before and at peak torque (4650 rpm in my case) and leaning out to 12.5-12.7 5000 rpm till redline. I gained up to 40 rwhp and torque in some areas especially at 4000 rpm

That is awesome. Do you guys think this would hold true for my older gen 6?

[Matt_lq4]

That is awesome. Do you guys think this would hold true for my older gen 6?

There are so many variables that you would have to experiment and see how it responds. Some tuners have had best of luck with a power enrichment afr target number that's the same all the way across the rpm range (12.4 for example) and some have chosen an ignition timing value that is also the same at full throttle across the rpm range. While others have seen the opposite. Every combo seems to be a bit different so you'd just have to experiment to find that golden recipe.

[Obsolete489]

Some dyno time would be a huge help at this. Although I suppose if I do a bunch of WOT runs and see how the airflow responds to different changes that would give me an idea of what is working.

[Matt_lq4]

Some dyno time would be a huge help at this. Although I suppose if I do a bunch of WOT runs and see how the airflow responds to different changes that would give me an idea of what is working.

A dyno or 1/4 mile would be the best as even the torque pid isn't accurate. I've been on the dyno many times and my torque pid value definitely wasn't consistent with my actual numerical gains in power that the dyno spat out.

[cal30_sniper]

Is there any way that you could go through and post up the missing images? I was interested in what your High Octane Spark Table worked out to be, but the image doesn't seem to be working anymore. Thanks!