Cylinder Volume - used for SD calculations?

[turbo_bu]

Does anyone know if the cylinder volume {B0104 in EFILive} gets used for doing the SD calculations for airflow? There are several posts out there that suggest it isn't used, but fumbling through the code kind of shows that it is used. At least for a part of the SD calculation of airflow. I am not quite sure where in the overall logic this part is, but it at least references cylinder volume.

Reason for asking is I am having to tweak my airflow #'s so that I can use more / all of the spark based timing tables. These tables are based on grams/cyl and not just MAP vs. RPM. In order to adjust the airflow, one method might be to just simply adjust the cyl volume.

[antus]

Which osid are you talking about?

[turbo_bu]

Mainly looking at the 512 kB OS's.... say a 2001 OS 12202088. At least that is one which I found a copy of the disassembly for.

[turbo_bu]

I think I answered my own question. I played with my bench top 0411 and faked in some signals to think it was running. I logged airflow stock, with cylinder volume doubled (2x) and then did a run with stock cylinder volume but 2X VE's.

Setup: SD mode (only connected to an IAT, MAP, ECT, TPS and RPM)

Doubling the cylinder volume did nothing to change the logged air flow (either grams/s or grams/cyl).

Thought I would make sure I wasn't crazy, so flashed it again with the VE table doubled (took whole VE table and multiplied it by 2). Yup - logged air flow increased by 2x.

I haven't quite figured out all the air flow calc's in the OS yet, but it appears that if you are scalling a tune, then messing with the cylinder volume won't do anything for you.

[yoda69]

Cylinder volume is usually used for fuel calculations based on the airflow.
Doubling the cylinder volume should also double the injector pulse width.

[NSFW]

I'm pretty sure it does get used, but I'll admit that I'm not 100% certain. It definitely appears right before a call to a function that does a lookup in the VE table, though.

I wonder if the numbers that you are logging might mean something other than what you think they mean... For example I did some logging last week and was surprised that the MAF I calculated from Load * RPM was about half of the MAF value I was seeing in the log. It turns out that the MAF value from the SAE PID is basically just what the MAF sensor reports. I'm running SD, and my MAF sensor scaling curve is quite a bit off.

What are you using to do data logging? What software, what PIDs, what memory addresses, etc?

[ShorTuning]

Yep it is only used for the VE table to display the correct % efficiency. Changing just that parameter will do nothing to the fueling.

[turbo_bu]

NSFW - I am using EFILive to log PIDs and to iterate on the flash file. The air flow PID's that I am loggin are: CYLAIR (gram/cyl), DYNAIR (gram/sec) and DYNCYLAIR (gram/cyl). I also added in the spark and IBPW PID's this go around.

The results were interesting: the airflow PID's still showed the same things as before. This time though, the injector pulse width PID's didn't do ANYTHING! They stayed at 0.636 msec (appears to be {B3701} Inj PW volt adjust) no matter what air flow was being calculated. I am guessing that this is due to me not having any load hooked up as injectors (and yes, I checked afterward and there was a DTC for the injectors ... go figure).

Funny enough, the spark PID did appear to be tracking the calculated airflow PID's. I guess I need to throw in some load on the injector circuits to see if that helps with getting reasonable IPW data.

[antus]

yeah if there is a DTC set on outputs they wont be operating.

[turbo_bu]

This is probably another stupid question, but if this cylinder volume variable is not used, then what value for engine displacement is used for the SD calculations? FWIW, I re-ran my little test with making a change to the engine type variable (found in most XDF files, but not in EFI Live), and again it didn't change the airflow results. Making the change to engine type did show up in EFILive under the Calibration screen though .... so it at least did something!

I guess that there might be another variable that gets used, or maybe GM decided to pick an average displacement and just adjust the VE ???