Side effects

[SSpdDmon]

I've been talking with a few people lately regarding the 'old school' way of tuning and the 'new school' way. In other words, the fudging the commanded fueling tables, injector tables and what not to get the desired reading through the WB vs. tuning the VE/MAF and all.

Personally, I don't think one way is any more wrong than the other. But, what I'm curious about is....what are the side effects of either way?

If we use the new way for example, what are the side effects of rescaling the VE/MAF? Don't A4 cars use the MAF's readings for trans calculations?

I guess what I'm getting at is.....what are the things going on in the background, that we don't see (burried in the source code), that may be affected?

[redhardsupra]

send me an email, i got a new paper i'm working on describing the tuning process mathematically, so you'll know exactly what's missing when ignoring x sensor or y table...

[SSpdDmon]

send me an email, i got a new paper i'm working on describing the tuning process mathematically, so you'll know exactly what's missing when ignoring x sensor or y table...

saj79 at aol dot com

[dc_justin]

When tuning the "old" way, calculated airmass/air flow is incorrect, yielding inaccurate spark reference, inaccurate torque calculation, inaccurate shift pressure lookup.

The "new" method, when done properly, yields a set of tables that closely describe the engine's ability to pump air. Assuming an accurate IFR table, everything else will fall in line properly and there will be no side effects.

The MAF isn't used for torque calculation any more than it is used for spark reference. The dynamic cylinder air calculation/measurement is where the air mass number comes from that is referenced against the Optimal Timing table and used to calculate torque.

[SSpdDmon]

When tuning the "old" way, calculated airmass/air flow is incorrect, yielding inaccurate spark reference, inaccurate torque calculation, inaccurate shift pressure lookup.

The "new" method, when done properly, yields a set of tables that closely describe the engine's ability to pump air. Assuming an accurate IFR table, everything else will fall in line properly and there will be no side effects.

The MAF isn't used for torque calculation any more than it is used for spark reference. The dynamic cylinder air calculation/measurement is where the air mass number comes from that is referenced against the Optimal Timing table and used to calculate torque.

The thing that's tripping me up is, if you stick a MAF sensor on a calibrated flow bench with the lid/bellows/filter to get an accurate representation of our intake setup while measureing MAF frequency, those numbers are going to remain consistent when airflow changes. So why, when we change the airflow or velocity of the air coming into the engine with things like camshafts or blowers, why would those numbers be any different?

[redhardsupra]

the air tract is different so the airflow's path is differnent. remember that the maf sensor has one tiny element in a relatively large area. airflow in a pipe is not uniform, so if the airflow will not take the same path as on the calibration bench, then different amount of air will go around the actual hot element cooling it differently, causing different numbers to show up.

[zapp168]

I seemed to have missed the memo somewhere, what is this "new" vs. "old" you speak of? Yes, I am new, but at least getting more and more confused with each new day.

[SSpdDmon]

I seemed to have missed the memo somewhere, what is this "new" vs. "old" you speak of? Yes, I am new, but at least getting more and more confused with each new day.

The old way is using something like the injector flow rate table or the commanded fueling in open loop table along with the PE table to get the desired AFR without changing the MAF or VE tables. Granted, the numbers in those tables will be innacurate. But, the goal is getting the WBO2 to read what you want while spending as little time fussing over perfecting tables. It's how shops continue to tune to this day, even with all of the discussion regarding SD and VE tuning that's been going on for the past 3+ years.

My question is merely to focus on the source code and how the PCM interacts internally. I hear of GM engineers laughing at those who use the VE table as a way of creating a SD tune. I don't necessarily believe everything I hear. I was just hoping those who have the ability to crack the source code and create a brilliant piece of software (like EFI Live) might be able to chime in and clarify a little for me.

[joecar]

Regarding the MAF and what it sees...

My simple-minded understanding :
the air path into a motor behaves in a manner consistent with waves and pulses;
when a valve opens and closes, the airmass at the valve is interrupted, while the airmass upstream continues on due to it's momentum, and some time later it hits the closed valve and relfects back;
the back reflection is "modified" by the stopped airmass (they mess with each other), and it looks like a "shaped" pulse;
the back pulse interferes with the forward air, so resonances (various local spots of high pressure, like waves interfering) show up (and the intake length can be tuned to spread these high pressure points to promote cylinder fill).

Meanwhile, the MAF sees forward air pulses, backward air pulses, steady air, oil from the K&N, oil from reversion (back resonances) caused by cam and valve events...
there's a lot going on...
reminds you of AC + DC + standing waves (AC going both directions), VSWR...

So the MAF in a live operating environment behaves alot differently than one in a lab environment.
The MAF isn't the simple device it appears.

And I am tired now...

Only my $0.02...