MAF Conversions

[SRavet at bangate.compaq.com]

RABBITT_Andrew at mv8.orbeng.com.au Wrote:
| 
| 'Everyone' talks about MAF conversions of existing EFI systems but can 
| anyone answer me a few questions about the whole exercise?
| 
| 1- what does a MAF sensor offer that a MAP and inlet air temp sensor 
| don't?  (or what do people think it offers?, ie what are the main 
| reasons for the conversion?)

MAF adapts better to engine mods.  SD systems use a pre-calculated 
volumetric efficiency for your engine, while a MAF system actually measures 
the air entering the system. An SD system can compensate somewhat for 
changes like headers or a new intake, but only when it is in closed loop 
mode.

Someone else asked:
| But you can calculate Mass Airflow from manifold temp, air density and 
| engine speed.  Why is this so inferior?

The engine speed part is the limitation.  If you make an engine mod that 
increases your rev limit, or changes your VE at any rpm, you have to 
recalibrate the look-up table.  A MAF based system would just measure the 
increased flow.  Closed loop operation will see a lean condition after 
these mods, and adjust accordingly, but that won't help your WOT, when the 
lookup table is used by itself.


| 
| 2 - are analogue (voltage) output devices used more commonly than 
| frequency output?
| 
| 3 - how are they normally sampled in these conversions, synchronously 
| at a determined crank angle, synchronously at any angle at all, or 
| asynchronously?
| 
| 4 - how do you know that the airflow you're measuring is actually 
| there?  Do people just slap them on and hope, or is some science 
| applied to make sure inlet manifold resonances are not upsetting the 
| signal?
|
| 6 - what kind of manifold filling compensation do people use?

I think usually they are put far enough upstream that they don't see any 
intake effects.  Isn't that one purpose of the plenum?  Some of the Ford 
people here had talked about modeling the intake using differential 
equations or something, but that seems a little complex for a DIY project. 
At least, it is for *my* DIY project.

Can anyone here recommend books about control system theory?  Books aimed 
at the experimenter, that is, not textbooks.  I had a controls class once, 
I won't mention what my grade was.  Let's just say that I barely didn't 
have to repeat it.  Surely some has written an easier-to-understand book on 
the topic.

| 
| Andrew Rabbitt
| Orbital Engine Company
| 
| 
| 
| 

--steve


Steve Ravet
sravet at bangate.compaq.com
Baby you're a genius when it comes to cooking up some chili sauce...