Mike Z28

Installed the BW MAF, new bin, and some rewiring (not a big deal). The documentation that came with the MAF was easy to follow and all the necessary parts (electrical) came with the unit. The engine started right up and I took the car out and put some heat in the engine and drivetrain. This car is an animal, it has no traction in first and second and pulls very hard through 4th (didn't have enough road or ***** for 5th and 6th). The kit came with an Ostrich emulator and BW wanted some data after it was installed and E-mailed a new bin after looking at the data. I am impressed with this product and their expertice.

bcollid

Now that sounds pretty cool.

I'm curious what kind of changes they made to your MAF tables

Is Blower Works MAF the same diameter as our stock MAF

did you take any readings or data logs before the blower Works MAF

Specifically do you have any data on increased airflow through the engine.

I like their approach of providing you a new BIN to go along with their MAF.

I've been skeptical of other MAF bolts on

Mike Z28

my first attempt at doing anything with the ecu was loading in the new bin from BW so I can't even attempt to answer any MAF table questions. info from the last data log was 340 gm/sec @5750rpm 9.72 ms bpw 972 mv on the o2. The MAF is made for blower applications and BW is working on a plug and play for Bosh conversions. They make 3" and 4" MAFs, I'm using the 3" unit. Mike

tequilaboy

Since the new sensor has much more range than a stock MAF, the tables are adjusted to fit the new sensor's transfer function for the intended housing. The ecm's control range is also extended to suit the increased range capability of the sensor.

In this case, the range has been doubled to provide 510 gm/sec measurement capability with fuel control over the entire range. Since he's flowing around 340 gm/sec now, he will have plenty of reserve capacity for future mods.

No absolute flow comparisons can be made in this case, since the stock MAF and calibration can only support 255 gm/sec. The actual flow of 340 gm/sec as measured by the new sensor is beyond the range of the stock sensor.

bcollid

A couple of questions for you:
1) Do you know/suspect that the stock MAF can actually only flow 255gm/sec or is it that the stock MAF might allow more actual airflow but just can't report over 255 gm/sec to the ECU

2)As you move to WOT and Power Enrichment mode takes over, does it really matter if the MAF can report something like 340gm/sec

3) Wouldn't you suspect a simple test could be made to compare airflow between the stock MAF and the BlowerWorks MAF say at some Rpm and/or engine load.

tequilaboy

Unknown. The Bosch sensor may continue to ouput a useable signal above the current 255 gm/sec value at 4.71 volts and above.

PE mode only alters the target AFR. This method can be used to accomodate excess airflow to a point, but it has its limitations, and will only provide so much fuel.

It is not flexible for changing conditions or variations in throttle position within the valid PE range. You basically need to set the target AFR for worst case conditions, and run rich under all other condtions while in PE.

More MAF range simply means more accurate fueling over a wider range of airflow, with less reliance on PE and/or AE modes to provide suplemental fueling.

Sure, scan data could always be compared under similar conditions, but it would be difficult to separate calibration differences from actual differences in airflow. Too many variables to be conclusive.

bcollid

I'm Curious how Blowerworks could extend the ecm's control range. I thought the 256 or 255 max value was tied to the 16bit nature of the ecm
Any ideas?

tequilaboy

By scaling.

The standard airflow signal is a 16 bit value with a resolution of 0.00389 gm/sec.

So 255 gm/sec is normally represented by an internal value of 65535.

Now think of the airflow signal instead with a resolution of 0.00778 gm/sec, or even 0.01167 gm/sec. The same internal maximum value of 65535 can be made to represent any airflow value, dependent only upon the choice of scaling factor.

Lemme

255 is 8 bits. Isn't the ecm an 8 bit one?

tequilaboy

The fuel bpw calculation is done with 16 bit math using the 16 x 16 multiplication subroutine. This calculation uses the airflow, injector constant and AFR target (which are all 16 bit values) to arrive at the appropriate bpw value.

Pete K

Interesting.

Lemme

From what I can see Tunerpro RT won't let the g/s go over 255 even when you change the MAF table scalar constants.

On the schematic for the 165 it can be seen that the data bus is only 8 bit (D0 - D7):
http://www.exatorq.com/ludis_obd1/1227165schematic.html

I think I remember reading that the ecm is a motorola (6800?)

tequilaboy

The MAF tables contain values ranging from 0 to 255 in order to represent the airflow which corresponds to the voltage output of the sensor. The sensor's output voltage is expressed internally as A/D counts ranging from 0-255. Each count is equivalent to 0.02 volts.

To arrive at a useable airflow signal value, the raw A/D counts are multipied by a factor and then input to the appropriate 2d lookup table, the result is interpolated and filtered to form a 16 bit value that represents the airflow for the number of A/D counts (or voltage).

The MAF table and scalars themselves are 8 bit values and are limited to 255.

A value of 255 has a different meaning in each table depending upon the scalar. In table #1, with a scalar of 23, a value 255 would represent 23 gm/sec.

In table #6 with a scalar of 255, a value of 255 would represent 255 gm/sec.

Taking this variable scaling concept a step further, consider changing the scaling so that a table #6 value of 255 (with a scalar of 255) could represent 510, 765 or even 1020 gm/sec.

If the sensor has sufficient range for the airflow, and the bpw calculation is rescaled accordingly, then the appropriate bpw can be calculated over the extended flow range. It all boils down to the sensor's range, and the scaling of the signals involved.

The 8 bit A/D converter is the only real limitation in the system, but this still provides plenty of signal resolution for idle and cruise airflow and is sensitive enough for accurate fuel control at elevated airflow, even with large injectors.

bcollid

Got it. PM me your email address and I'll buy you a beer from yougotbeer.com!!!

The beer is a bribe for just a couple of more questions. You seem to be the guy with the answers!!!!

1)I run a good breathing 383. My stock MAF is pegged and I've been using PE fueling to keep from going lean at WOT. Sounds like I should get an aftermarket MAF with an extended range. No scaling is going to help me. Does this sound right? If the MAF signal is pegged.. not much else I can do. Sounds like I should look into this blower Works MAF Sensor.

2) Now here's a curveball. There's also a table called Maximum Airflow vs. RPM which shows an upper limit of 255 and no option to scale this value so how does this work?

Say I have a new MAF sensor that can report 300 gms/per sec as a voltage range that's acceptable to the computer. Isn't this Maximum Airflow vs. RPM table going to override all the other cool stuff that was done with Scaling?

What gives???

Lemme

Just another thought. Can the existing MAF be recalibrated to read say up to 350 g/s instead of 255 g/s?

bcollid

I'm pretty sure the only way to do this would be to change the electronics in the MAF sensor so that 255 gms /sec sends a voltage of say 3.2 volts instead of 4.7 volts

hey, thanks for jumping in on the 16 bit and 8 bit stuff. That really cleared up a couple of points.

Lemme

If the existing MAF does actually read past 255 g/s then it could be possible to scale the readings down a bit at the MAF. Could mount a little black box on the outside of the MAF which scales down the voltage signal.

Lemme

The limit of 255 still remains. It just means something other than 255 g/s. For example, 510 g/s (multiply what you see by two). Therefore the a/flow vs rpm table still operates as per normal. The fuel tuning (AFR) ensures more fuel (approx double) is injected via the base injector pulse width (bpw) I am assuming.

Here is my maf mapping. It can be seen that after 4.71 volts the signal is capped at 254 g/s. If the 254 limitation wasn't there potentially it could be measuring over 300 g/s.

bcollid

Yeah I think you are right.

Also on the stock MAF.... I bet a guy that knows what he is doing could put a resistor or something on the stock MAF for like .39 cents and that's all it would need......

See ya I'm going to sleep