×

Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

# Porsche 911 reflash tuning, airflow calculations / VE logic

### Tech Articles

Discussion and questions related to the course Practical Reflash Tuning

There are a few curiosities and questions I have regarding Porsche 991.1 GT3 / Bosch MED17.1.1 ECU logic. I am using HPTuners MPVI2 and Beta VCM in order to have access to all the mass airflow correction tables.

If anyone familiar with Porsche's fueling logic has time to read and answer that would be helpful.... I aspire to reciprocate once I'm more familiar with this platform.

The load scaling strategy in this ecu is proving to be a bit harder to grasp than traditional VE strategy, some of the axis labels in HPTuners are hard to comprehend, and to be fair it looks like many of the VE related / airflow tables have been moved exclusively to the Beta version of VCM editor.

I have been attempting to understand the various Mass Airflow Correction tables by modeling in excel alongside vvt targets and building conditional datalog functions to better understand the relationships.One of the things that's still a bit confusing to me is the axis description on "Fill up efficiency" and "Fill up conversion" tables being labeled with "exhaust valve average closing angle" as an axis with a 50* range from 223-273* when the exhaust camshaft is only physically capable of 30* retard. The intake camshaft indeed has 50* of advance, so I am wanting to confirm that the axis is labeled correctly as exhaust

it makes more sense intuitively to have this table be intake adv (-50 - 0) since the intake range fits the axis much better than exhaust range.

Perhaps the extra range 223-273 is just padding and not used? - if this is the case, where on the axis does 0*-30* exh represent upper and lower table bounds in the 223-273 range? Either 223-253, 233-263, 243-273 or somewhere in between?)

The "Valve Overlap" Airflow characterization tables represent 85* of total relative motion (-30 thru +55* overlap) out of a possible 80* of actual possible camshaft relative motion between int+exh; so just 5* of padding which makes perfect sense.

I have defined valve overlap as a math based logging parameter and will be experimenting with which commanded valve timings correspond to which areas on these tables, but so far my attempts to tweak the mass-airflow model have not resulted in predictable outcomes in terms of achieving tighter fuel trims in the targeted RPM/Valve motion range. Searching for learning resources that might assist in better understanding the logic of Porsche's fueling strategy (pressure on filling conversion tables etc) that might save me some trial and error but have not had any luck. If anyone has anything please let me know!

There is also an odd behaviour that I've observed even when running on 100% stock calibration and 100Oct fuel, where only one cylinder is showing intermittent spark retard at certain loads and rpm's.

When I logged the car on stock calibration + pump gas, there were occasional spark retard events distributed across all cylinders as you would expect, but this single cylinder in particular would always register more retard than the others. On 100Oct, none of the other cylinders will register knock besides the single problem cylinder. I have reduced ignition timing across the timing map and get the same behaviour, thinking there might be some vibration or perhaps internal damage, but oil analysis comes back clean.

I am wondering if there is some undefined per-cylinder timing retard that's correcting for something other than the presence of knock. I have yet to attach det-cans and listen to the engine while it retards this cylinder.

Porsche 991.1 GT3 HPFP and ethanol fuels

I am not finding much information on the long-term compatibility of the OEM equipped HPFP and ethanol containing fuels. If I have enough injector headroom (might need to rig up an oscilloscope as there is no injector PW logging parameter in VCM scanner) I'd like to run the car on E85, but I am concerned about the lack of lubricity and fuel delivery headroom on these engines.

Homogenous DI and soot formation at specific AFR's

Is there any general rule on specific AFR's that we should avoid to help prevent the formation of soot with a homogenous strategy DI engine? It seems that Porsche's factory fueling targets start off very lean and stay as lean as possible until an exhaust gas / catalyst temperature model intervenes and targets a far richer AFR than one would think is ideal for a DI N/A engine.... without spending much (if any) time in the middle. I am positive that targeting a more sensible best-torque AFR in the primary fueling target tables will bring the power up a bit, but scratching my head as to why porsche would utilize this somewhat odd fueling strategy and the only thing I can think of is that certain, specific AFR's might form soot at a much higher rate than a leaner or richer afr. Is this a thing?

Appreciate any response, knowledge, feedback. Knock on wood someone here has familiarity with Porsche ECM!

Bump:

I am still seeking more knowledge about the air charge model that Bosch uses to calculate airflow. The pulse compensation tables make sense in theory, but the changes I make to these tables do not produce expected results when logging the car. Anyone with experience altering AirCharge parameters feel free to chime in.

You are the bleeding edge. Your best bet is to get hooked up with the folks at HPTuners that are decoding the tables. I'm sure they would appreciate having an interested and knowledgeable tuner assisting figuring out the ECU behaviors.

Good Luck!