[Diy_efi] Speed-density vs. MAF/MAP...

[Alexei Pavlov]

> Why don't we take 32..64 MAP samples per revolution?
> > (at least to get datalogs to support the
> > pre-intakevalve-opening theory).
> 
> I am working with someone who is going to be doing
> some significant datalogging, and we are going to
> outright test a lot of the ideas that have come up in
> this threat to find strengths and weaknesses, useful
> and less useful methods of doing things.  I've become
> immensely curious, and it's time to find out the
> correct answers.

Very interesting thread. I'm a little late :-)

I'm currently working on the same kind of system. I've
finished a ST7 based circuit connected via RS232 to a Linux
based laptop. I just need 1-2 days to install all that on my
car (1.8L atmo 4cyl). 

The measures I'll do will be:
- hot film MAF (the stock one from my car)
- Bosch flap MAF + temp sensor (to understand the flap MAF)
- 100kpa MAP
One sample set per induction phase (2 per revolution).

I know that I have big oscillations around 2500rpm (to improve torque),
I've already logged MAF data in a wav file.

I'm still hesitating how to sample the MAP sensor. I'm sure that must
be done synchronously to the engine revolution, as this allows efficient
digital filtering with always the same 'virtual' time constant (the
sampling
instances are attached to the crank position).
The problem is that intake air pulsations evolve with RPM and with the
air density (thus pressure and temperature), as sound speed is density
dependent.

If I do 1 sample per induction phase the danger is to sample sometimes
at max of waves, sometimes at mins (undersample) as sound speed does not
depend
(unfortunately) on the RPM.
With 2 samples it's better, but still not enough.
The higher is better. If I decide to sample at a 8 s/phase rate I can
hope
to oversample (and thus filter) biggests oscillations. Where is the
reasonable
limit of oversampling ?
Research articles never go above 4s/phase, but don't explain why.
And I have just a poor 8bit 8Mhz uproc that must sample 4 sensors
through
the only ADC :-)

Any opinion ?

Alexis

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi