Bill Chase

looking at various oem tune files. is there a formula to convert maf lv8 load numbers to kpa?

RBob

iTrader: (1)

Not a direct conversion, but you should be able to fudge something together that is close enough. The MAP reading is an absolute pressure value. While LV8 is derived from RPM and airflow. From the MAF Miscellanea thread:

LV8 = inverse RPM * airflow * scalar

This causes a higher LV8 at a lower RPM (given the same gms/sec).
And conversely the higher the airflow (gms/sec) the higher the LV8. The scalar may be found before the beginning of the MAF tables.

RBob.

ULTM8Z

Too bad there isn't a way to wire in a MAP sensor into some unused 0-5V input on the ECM and then read the data in TP. Then you could derive a relationship empirically by comparing the MAP data and the LV8 data.

Fast355

iTrader: (2)

LV8 is the predecessor to Gms/Cyl that the LS based controllers use for load scaling.

Fast355

iTrader: (2)

I have logged the RPM/MAF derived Gms/Cyl aka Cylinder Air on LS controllers vs RPM and MAP. Those numbers increase with VE and peak near peak torque, then taper off at high rpm.

tequilaboy

LV8 literally represents the grams of air in the cylinder or gms/cylinder. In our 5.7L V8 engines, LV8 is scaled so that 100% load (or 255) is equal to 0.8 gms/cylinder.

(gms/sec)/(rev/sec) = gms/rev. (gms/rev)/(cylinders/rev) = gms/cylinder. 4 cylinders on intake stroke per rev for a V8 engine with 4 stroke cycle.

If properly scaled for a given number of cylinders and displacement, this value should represent something close to 100% cylinder filling. Assuming the VE, cylinder volume, temperature and manifold pressure are known, you should be able to calculate the mass of air in the cylinder and compare against the known 100% value for reference.

For practical purposes with naturally aspirated applications, an LV8 of 255 can likely be treated as if it were analogous to 100 kpa, neglecting the effect of temperature.

In this (supercharged 305) example, I've re-scaled the LV8 for range up to 1.2 gm/cylinder, but it is still numerically represented so that 255 = 0.8 gm/cylinder to keep the end result on the same (familiar) scale: https://datazap.me/u/tequilaboy/feli...8499&mark=8394

tequilaboy

You can also cheat a bit, and convert your injector pw to load, since they should be directly proportional to each other (for a given target afr). Take your maximum pw value and call that 100% load (or 255 if you will) and create a virtual channel that reads accordingly from 0-255.

Load and ipw signals isolated: https://datazap.me/u/tequilaboy/feli...mark=8360-8373

Load, ipw and target afr: https://datazap.me/u/tequilaboy/feli...mark=8360-8373

Note: The target afr is load dependent in this example, so this contributes to some additional ipw signal variation/noise compared to what would be seen with a more constant target afr signal.

Bill Chase

it would be easy enough to wire one up. and log it its just a 0-5 volt intput. any extra ecu channel capable of that could be used. or even a laptop could be used with a cheap arduiano piece?

most guys hit a wall with the stock ecu modifier tables pulling timing, adding or subtracting fuel etc. and they go to a stand alone. in my case i am using a stand alone but want to integrate as many "safety" timing and fuel modifiers as i can since its a street car. the trouble is stuff like the lv8 tables, and other things that are difficult to decipher.

Bill Chase

good info, and thank you for the response. I figured the max lv8 would correspond to 100 kpa and wot isnt that difficult to get a decent safe tune, even if its far from optimized. . i am actually more interested in the lower lv8 numbers, trying to get some economy and drivability with safety for the occasional tank of bad gas, and my valvetrain is just loud enough that using a knock sensor isnt an option, and my car is a stick, so part throttle timing and fueling is of particular importance to me. the drivability stuff the more oem sbc tune files i study, the more i begin to wrap my head around giving the engine what it wants, and keeping the tune on the safe side. and the further i get into this, the more i realize the oem ecu were/ are actually far superior to any aftermarket ecu. the trouble is their primary programming is based on emissions complience, then surviving warranty, performance is the last priority. but still, most holley, dfi, etc are actually very "dumbed down" in comparison to even the late 80's odb1 factory ecu. shame someone hasnt completely cracked their code, the emissions outputs for egr, canister purge etc would be enough if they could be repurposed

tequilaboy

Different application entirely (turbo car), but another example just to illustrate how closely related load, ipw and manifold pressure really are to each other: https://datazap.me/u/tequilaboy/evo-...2285-2305-2316

Fast355

iTrader: (2)

Valvetrain usually does not mess with a knock sensor. I have run a solid roller cam with roller rockers and double springs and had a knock sensor that functioned as designed.