Red rooster

The MAF unit scaling is done by a simple software calibration in good old Motronic M5.2 .
This can be changed to accomodate the required airflow within reasonable levels.
The OBDII data simply outputs what it has been told and need not be 100% accurate.

Maybe this discussion has to start from a different point ?



Geoff

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KS400200 , the oldest 964 on Rennlist , unless you know differently !

Jean

I personally I am totally confused by this MAF discussion in the last few posts and how it relates to engine HP

Jussi

You can't be confused after you understand that 8.5 or 9.5 hp / lb/min thing.
You can measure engine's air flow with MAF - that's what it is for.
Flow times efficiency is power..
Engine is an air pump and powerful turbos help that flow

Geoff: There is a fixed converting table for air flow (MAF), totally 256 values, max is 4.98 V= 1546kg/h value. Motronic 5.2 uses that(+few others) for fuel supply calculations.

Red rooster

js-911,

Please excuse me if I seem rude but what you are describing is a basic , alterable calibration .
Production MAF maps are routinely reset in DME control functions for different calibration requirements. Perhaps the most trivial example is the use of the same DME hardware used for different motor size / power requirements .
It is not a "cast in stone " situation that a MAF calibration map is unalterable !

I only raised this ,as debate on bhp seemed to being linked to OBDII MAF flow rate numbers . These can and probably will be altered for motor performance
but can be organised to give apparently standard OBDII numbers .

I will leave you guys to your debates !!


Geoff

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KS400200 , the oldest 964 on Rennlist , unless you know differently !

TB993tt

So are you saying that a MAF reading from the Hammer can be artifically altered to suit ?
ie it reads 1546kg/hr but in reality is 1555kg/hr

We are not arguing about the limits of flow rate (yet ) I think YOU are the one confused maybe ?

Red rooster

TB993TT ,

Sorry , but I must stop this now . I have direct DME development experience for vehicle manufactures. The M5.2 system you are talking about, is by now ,
relatively pretty old and well kown.
The statements you are challenging are well known and I could bore you with examples.
I was far more interested in how you guys were arguing other points .

Sorry to have intruded your lightly technical discussion.

Geoff

Jean

Red Rooster,

I was hoping I would get some objective scientific input from yourself concerning the BMEP discussion above. Namely on two fronts:

1- N/A engines:

Would you agree that there are no two ways around this. If an engine is showing a much higher BMEP (5%+) than its sibling engines (964 vs 964, 993 vs 993, 996 vs 996) or race engines with some similar mods, then the dyno measurements must be optimistic. I am assuming that someone like yourself who has worked extensively with these cars recognizes that Porsche factory numbers are not pessimistic but rather realistic and in any case they consitute THE bench.

2- Turbo engines:

While the calculations by going back to atmospheric levels might not be spot on due to heat, stress, etc.. it does however provide an accurate indication when one compares turbo vs turbo engine. Probably as I mentioned earlier comparing BMEP for a turbo vs N/A engine might need some adjustments for heat and load vs a straightforward calculation, but it cannot be very far off, as numbers are pretty much in line with differences in air flow and BSFC between those engines. i.e a turbo engine at atmospheric pressure is 10-20% less efficient (at atmospheric levels) than its N/A counterpart as a result of lower compression, no twin plug, differences in heads and intake/exhaust etc.

I would be interested to hear your POV, and if not in line with the thinking , why not.
Thanks.