MAF v SD

[robert joseph dingli]

Hi all,

I returned from a short hiking trip to find lots of interesting articles
on EFI algorithms.  Anyway, this is the first of my contributions for the
week.

Steve wrote
> 
> The advantage to MAF is that the computer can automatically adapt to engine 
> modifications like a less restrictive exhaust or heads that flow better, 
> right?  SD requires that the volumetric efficiency table be updated any time 
> mods are done to the engine.
> 
> --steve

I've never used a MAF sensor and would guess that you are quite correct here.
There are a couple of important points to be made though :

Firstly, I presume that in the context of DIY EFI one will be aiming to
design a system which is adjustable and thus any major change such as an
engine mod will simply require some recalibration.

Secondly, the hardware required for SD system requires one less component
(the MAF meter) which are regarded as fragile at the best of times.  

Lastly, the SD map between speed/load and fuel output doesn't just reflect
volumetric efficiency.  It also reflects desired air fuel ratio which is
also a function of speed and load position.  When I drive down the highway
tuning my car, I'm not aiming to estimate volumetric efficiency, but the
output of the whole system which includes the way the engine performs from
accelerator feel and the output from an EGO sensor in the exhaust.  I aim 
for a very lean cruise, rich WOT and near WOT, and a stable idle.  (I don't
have to worry about emmisions of course.)  Any similar MAF system would 
require a similar map and similar programming.

Robert
-- 
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             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 344 7966                           (+613) 344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
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