Main spark vs. airflow??

[sfogg]

In the low and high octane spark map tables what is the airflow axis based on from the scanner? Is that airflow in seconds, minutes or ??

Basically I'm just trying to figure out which map point I'd be in on those tables from the scanner data. It doesn't seem to have a direct correlation to airflow data in the scanner. Is it maybe fuel/cylinder per second or minute?

Shawn

[jimmyblue]

It looks like gm/sec on the Y axis and RPM on the X axis.

It looks like the scanner however logs in lb/min so you
would have to convert units (probably in Excel) or maybe
you get gm/sec if you select the Metric basis?

[sfogg]

" It looks like the scanner however logs in lb/min so you
would have to convert units (probably in Excel) or maybe
you get gm/sec if you select the Metric basis?"

Right, that is basically my question. How is the VCM arriving at the number it is using in that lookup table and how can I work back to that based on the scan tools logging?

Shawn

[jimmyblue]

I believe the MAF table is gm/sec vs Hz and the PCM
gets airflow straight from that. The lb/min format from
scanners I think is just a concession to red blooded,
metric system hatin' Amurrican mechanics ;D

gm/sec = lb/min * 454 gm/lb * min/60sec or a scaling
factor of 7.57 to change the logger output to gm/sec
basis. If your peak airflow ends up at about 300 gm/sec
by this scaling then I didn't screw up my algebra. On a
stockish motor anyway; more HP = more flow or course.

[sfogg]

I don't have my logs (or the software) in front of me but I think I saw around 30lbs/min max airflow. By the above that works out to about 227gm/sec.

However that still doesn't solve my question. The highest value in the spark tables was something like 1.2g/sec. Hence my not knowing how/what/where this value is coming from.

Shawn

[jimmyblue]

OK, I think you're talking about the "Closed Throttle"
spark table, which would be idle only. So the max
airflow there will be tiny; take the scale factor against
a datapoint that's idle, stopped and you should end
up with something that falls in range?

Hmmm... no, the high and low octane tables all have the
same 1.20 gm/sec maximum index. That's kooky.

I think this is a typo/error, the spark tables should be
covering the airflow range up to sane maximum (511
gm/sec). We'll have to see what the programmers say
about that, I guess.

[sfogg]

" Hmmm... no, the high and low octane tables all have the
same 1.20 gm/sec maximum index. That's kooky. "

Now we are on the same page.

The index is actually listed as g/cyl which is why I was wondering if perhaps that axis isn't even airflow at all but perhaps injected fuel. That would be closer to what I'd expect but I just really don't know.

Shawn.

[Chris@HPTuners]

the value is g/cyl (grams of air per cylinder). It is a measure of how much air is in each cylinder (related to load).

we are working on a calculated PID for the scanner to enable you to log this directly. The formula is:

g/cyl = MAF (g/sec) * 15 / RPM

[GarySmithZ28]

In case anyone wonders where the factor 15 comes from, here it is:

Load closely corresponds to intake air mass per engine revolution. Units are grams per cylinder. To convert airflow in units of grams per second (as measured by the MAF) it is necessary to multiply by the reciprocal of cylinders per second. In a four-stroke engine all cylinders are filled with air in two revolutions. Therefore, an eight-cylinder engine fills four cylinders per revolution.

Cylinders / Second = (Cylinders / Revolution) X (Revolutions / Second) = 4 X RPM / 60

Cylinders / Second = RPM / 15

Load (gms/cyl) = MAF (gms/sec) * (sec/cyl) = MAF (gms/sec) * 15/RPM

Example:

Calculate load in grams per cylinder if total mass airflow is 260 grams per second
at 6000 RPM

Load = (260 gm/second) * 15/6000 = 0.65 gm/cyl

[Chris@HPTuners]

for those v6 folks, swap 15 for 20