Hacking for Dummies... LV8?

[ezobens]

The dummy would be me ;-)
I'm trying to make heads or tails of all these tables and files (89' TPI ARAP bin in my case).
I see the term "LV8" appearing everywhere but for the life of me, I cannot find a definition of what this means other than "Load Variable 8", which means nothing to me.
What is "Load Variable 8" and what do the values on the charts mean (IE 32, 48, 64, 80 etc)?
If I understood what this unit of measure was, I could better understand what these tables are doing.
Anyone?
Thanks!
Elm

[RobertISaar]

Load Variable, 8-bit

might be a better description.

if you're familiar with OBD2 stuff, it is the equivalent of the mg/cyl(or g/cyl or xxx) value, just without any specific scaling value attached to it. it is a direct indication of the weight of the airmass that is in the cylinder.

a LV8 of 64 is twice the airmass of a LV8 of 32.

the reasoning behind there being no scale other than raw numbers is that usually there is a LV8 scalar in the calibration used to define the amount of airmass per cylinder to define as the maximum limit(LV8 of 255). if that scalar is changed, the actual amount of airmass that LV8 represents changes. this is how you can get an engine that struggles with a VE of 70% to achieve a LV8 of 255 and how something that can pull down 110% won't overshoot the maximum.

[ezobens]

Load Variable, 8-bit

might be a better description.

if you're familiar with OBD2 stuff, it is the equivalent of the mg/cyl(or g/cyl or xxx) value, just without any specific scaling value attached to it. it is a direct indication of the weight of the airmass that is in the cylinder.

a LV8 of 64 is twice the airmass of a LV8 of 32.

the reasoning behind there being no scale other than raw numbers is that usually there is a LV8 scalar in the calibration used to define the amount of airmass per cylinder to define as the maximum limit(LV8 of 255). if that scalar is changed, the actual amount of airmass that LV8 represents changes. this is how you can get an engine that struggles with a VE of 70% to achieve a LV8 of 255 and how something that can pull down 110% won't overshoot the maximum.

Robert,
Thank you so much for responding- I apologize but I'm still unclear how this all fits together.
Looking at the Spark Advance Table for example, I understand the RPM axis and the values that are in the cells are degrees of advance but I'm still not getting what the 32, 64, 80, 96 etc columns represent at the top? I see that the timing tends to be reduced the further right you go (higher LV8 column) but I'm still not seeing the connection. Does LV8 ALWAYS represent airmass and are these just relative values?

IE what is the difference of 2000 RPM at an LV8 of 80 vs 2000 RPM at an LV8 of 208 and how do you use LV8 to calculate what the value should be used for those respective cells?
Sorry if I'm making this more difficult that it is-
I just want to fully understand what is going on and how this all fits together.
Thanks!
Elm

[RobertISaar]

Does LV8 ALWAYS represent airmass and are these just relative values?

yes!

that is likely the simplest way i could ever explain it.

in the example of 2000RPM at 80 vs 2000RPM at 208, the difference is that for a LV8 of 208 to be calculated, there is 2.6 times as much airmass than at a LV8 of 80. real-world, this could be something like 250mg of air in the cylinder for the 80 value and 650mg for the 208 value. if MAF grams/sec values are accurate, then you could generate an equation to automatically convert the LV8 values into mg/cyl if you really wanted to.


how do you use LV8 to calculate what the value should be used for those respective cells?

that's the difficult part of your post to answer... and it will be different for every engine. that's the tuning process really, finding out what works best.

[buddrow]

It's basically a calculated load value. an LV8 of 80 2000rpm would be a lower load on the engine(higher vacuum) compared to an LV8 of 208 at 2000rpm. The farther you push the gas pedal down the more load you place on the engine. From what i understand just browsing through the ARAP bin, this bin cranks out a lot of timing advance at light throttle/light load. To calculate the appropriate value for X amount of advance versus RPM seems to be a crap shoot at best as I don't see a knock sensor to let you know if youre getting spark knock/detonation so you would have to "listen" for pinging/knock.

Hopefully I've cleared it up for you and not made matters worse. Robert, please correct me if I am wrong. It's been known to happen. :)

Buddrow

[ezobens]

Thank you both for your time!
I think it's finally sinking in..
I just need to realize nothing is ever truly cut-n-dried with this stuff and that trial and error is pretty commonplace.
Now I'm dangerous enough to shoot myself in the foot ;-)
Thanks again!
Elm

[RobertISaar]

Robert, please correct me if I am wrong. It's been known to happen. :)

what you're typing and what i'm typing look the same to me, just slightly different ways of getting to the same result.

[buddrow]

Robert,

We were apparently typing our responses at the same time lol. Had I just waited a few more minutes I could have saved some finger walkin :)

Buddrow