Corvette 6E bin with 4+3 transmission(1987)

[gta324]

Very interesting! What MAF sensor is used?

But the owner just wanted a "stock" chip modified for bigger injectors.

[tequilaboy]

Very interesting! What MAF sensor is used?

But the owner just wanted a "stock" chip modified for bigger injectors.

Fair enough. A light re-tune for the injector swap should be sufficient in this case.

The MAF sensor shown is from Blowerworks (including aluminum housing and meter). The tuning is based upon a collaborative effort between Blowerworks and myself to take advantage of the new meter's capabilities and to adapt it for use with the TPI 165 ecm.

The meter itself is similar to an SCT BA5000. At the current power level (480 rwhp at 9 psi), the system is hardly stressed. At peak flow, the meter's ouput is only about 4 volts. With a boost-safe 11:1 AFR target, 63# injectors are running around 60% duty cycle. The system has plenty of range to support more power assuming both the injectors and fuel pump(s) are up to the task.

[gta324]

Sounds great!

Is the spark tuning done in rpm vs load table? and does it allow you to tune SA vs boost in someway? I mean how does it calculate LV8 with that MAF and boost?


Anyhow...great work, should kill the 255gr/sek limit debate :)

[RobertISaar]

LV8 is essentially an early and more primative version of the "mg/cyl" value that you see referenced so often in OBD2.

in the end, it's an "airmass in cylinder" value with no specific scaling, since there is a scalar to adjust it to skew it to a higher or lower range in the calibration.

[tequilaboy]

LV8 is essentially an early and more primative version of the "mg/cyl" value that you see referenced so often in OBD2.

in the end, it's an "airmass in cylinder" value with no specific scaling, since there is a scalar to adjust it to skew it to a higher or lower range in the calibration.

Exactly. With appropriate scaling, LV8 can cover the entire possible range of gm/cyl and also serve as at least an indirect indicator of boost. In my case for example, the LV8 is scaled for 150% of the normal range which is sufficient. So, conceptually, my LV8 ranges from 0-382.5 instead of 0-255. LV8 values above 255 are typically in the boosted region. This approach provides 3 columns of spark advance adjustment in the main table to cover the boosted region.

Boost, no matter how interesting to discuss is somewhat irrelevant from a control standpoint. What is important is the flow, rpm, LV8 and air charge temperature. With these inputs, you can determine appropriate spark and fuel requirements for all conditions.

On a related note, to ensure sufficient fueling for boosted conditions, I typically set the PE AFR target as a function of LV8 instead of rpm. The spark advance can also be further compensated according to the air charge temperature which is available from the MAF's integrated IAT, however this is only effective if the MAF is installed in a blow-through configuration and is down stream of any intercoolers if present.

So to summarize, spark advance can be tuned at least indirectly for boost and also for air charge temperature.

[RobertISaar]

i'm somewhat unfamilar with 6E, so i took a look at one of the XDFs i have. from the looks of it, it uses multiple MAF tables and a scalar for each table, but no offset for the tables as would be found in the later MAF stuff. someone correct me if i'm wrong.

it also looks like the code is hard limited to 255 grams/sec without messing with other items to fool the ECM into delivering the correct PW.

[tequilaboy]

it also looks like the code is hard limited to 255 grams/sec without messing with other items to fool the ECM into delivering the correct PW.

Its simply a matter of scaling. Instead of grams/sec, what if we could rescale the airflow and fuel calculation into something else? Maybe kg/hr, lb/hr, kg/min? Hey, how about something like myriagrams/hr? WTF is a myriagram?

1 myriagram = 10 kg.

So we could now have a range of 255 myriagrams/hr. Converting from 255 myriagrams/hr to grams/sec gives us the following:

255 myriagrams * (10,000 grams/myriagram) / 1 hr * (3,600 seconds/hr) = 708.3 gm/sec. Roughly a factor of 2.778 to convert between grams/sec and myriagrams/hr. That's interesting.

Since 708 grams/sec is enough airflow for about 1,000 hp depending upon BSFC and AFR, 255 myriagrams/hr is plenty of range.

Adjust the MAF tables for the new units of myriagrams/hr, convert the other flow dependent values appropriately and we have enough signal range for about 1,000 hp.

Of course, we could always use a more convenient scale factor, but myriagrams/hr would be certainly sufficient.

Despite all of this, I'm sure the debate will still rage on.

[RobertISaar]

probably be significantly easier just to work in grams/sec.... just not the original code that's limited to 255(or 255 and 255/256, assuming 16 bit math).

converting it to work with up to 512 grams/sec is dead simple since the code already exists to do so in later PCMs. beyond that, it still wouldn't be that difficult to mess with.

[EagleMark]

WTF is a myriagram?

That would be an EFI headache! (migraine)