MAFS vs Speed Density TPI

[Tuck]

>Yet, a MAFS sensor based system is supposedly more forgiving of 
>performance modifications, and allows the use of a hotter cam.  The speed 
>density system requires a good vacuum signal to calculate air flow, and 
>hot cams don't lend themselves well to big, stable vacuum signals.

Ther eis a reason for this that I think I should point out, fortunately I
can give a real world example while making my point.  I was recently talking
with Peter Farrell at PFS about fuel and boost management stuff with a
product he sells for the third generation RX-7 and we got onto the topic of
the earlier second generation RX-7 Turbo's.  He told me that he was able to
run 14 psi of boost using only a voltage clamp on the MAP sensor (to prevent
the overboost fuel cut built into the stock ECU) because the computer could
tell that volumetric efficiency had improved through the MAF.  This is a big
advantage of an MAF EFI system on a car that normally has positive manifold
pressure under load.  If you increase volumetric efficiency without
increasing boost pressuse on a turbo equipped engine the EFI computer wills
till get the same information from the MAP sensor, so there is no way that a
speed density system can know that the actual volume of air moving through
has changed and adjust fuel delivery accordingly.

Justin "Tuck" Cordesman
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