[Diy_efi] pic based afm -> maf conversion

[Tom Visel]

Manifold pressure vs. RPM (speed-density) gives you a very handy way of 
giving fine control over fueling in known areas where a MAF interpreter 
would not.  MAF lets you play without paying as much, but if the 
playing's over, the keenest edge will be found with a speed density 
system tuned using a wide-band O2.  Either way, you would have to 
eliminate or make constant the ECM's barometric pressure input, as this 
would be compensated for twice otherwise - once in your black box and 
once when the computer tries to figure it into what it thinks is the VAF 
(vane air flow or volume air flow) sensor's output.

BTW, the reason for the ubiquity of MAFs on modern vehicles is for 
tighter emissions controls: to allow for the measurement of EGR flow, 
and to allow for a MAP sensor as a redundant system and for rationality 
checks to see if the MAF's calibration is drifting.  Almost every 
vehicle has both a MAF and a MAP these days (at least in North America.)

TomV


Ashley Evans wrote:

> Interesting.  I'd not considered the engine volume aspect of MAP (as 
> I'd not considered MAP at all)  but you state "MAP is the way to go" 
> if engine design is finalised, which it is...  Is this judgement based 
> purely on the fact that MAP has no intake restriction?
>
> As it's a PIC system changing parameters such as sensor voltage maps, 
> or volume "constants" wouldn't be an issue.
>
> Thanks,
> Ashley
>
> p.s.  no puns in *my* emails ;-)
>
> Tom Visel wrote:
>
>> With both MAP and MAF systems, you will have to map the new sensor's 
>> readings (and also RPM in the case of the MAP sensor) to correspond 
>> to the old sensor.  The advantage - if this applies in your case - 
>> with the MAP setup is that there is NO inherent restriction.  The 
>> advantage with the MAF setup, once mapped, is that it will compensate 
>> for changes in volumetric efficiency - cams, intake and exhaust, head 
>> work and such - simply by measuring the change in flow through the 
>> sensor.  With the MAP sensor (speed density) setup, you will have to 
>> reprogram for such changes as you make them.  If your 
>> engine/intake/exhaust system is fully developed, MAP is the way to 
>> go.  If not, then MAF gives the flexibility of...wait for it...
>>
>> breathing room.
>>
>> Sorry!
>> Tom "driveability technician" Visel
>>
>>
>> Ashley Evans wrote:
>>
>>> Thanks Richard,
>>>
>>> My application will never reach anywhere near 500bhp :)
>>>
>>> For what it's worth, I'm going to be using it two-fold.  one for 
>>> getting the mixture right, and running lean on light cruise.  Two, 
>>> for actually adding fuel when needed by fooling the ecu into 
>>> thinking there's more air than there really is.  I'm led to 
>>> understand that this will have an effect on the timing so I will be 
>>> paying extra attention to the knock sensor, and WBO2 when tuning to 
>>> find out what's really going on. We do have the advantage in the UK 
>>> that our cheapest grade fuel is 95RON, and 98RON is readily available.
>>>
>>> The MAF in question here is a Bosch unit commonly found on Vauxhall 
>>> Vectras/Astras and similar.  The cross section is slightly large 
>>> then the TB and quite a reasonable amount larger then the square 
>>> inlet of the original AFM.  Hopefully this will yield some WOT gains.
>>>
>>> My choice for using a MAF over anything else was based on the 
>>> experience of others,  I just wanted to do it home-brew style.  I 
>>> think it's easier to do than MAP from what I've read.  Less code, 
>>> and easier physical install.
>>>
>>> I guess what I really want to know is, can I get significantly more 
>>> power using MAP in my application?  It seems even if I could, I 
>>> would lose the finesse of MAF.
>>>
>>> Thanks again,
>>> Ashley
>>>
>>> Frey, Richard K wrote:
>>>
>>>>Sounds like you understand the merits of each.  I think the application
>>>>might determine the need.  Personally, I would not be married to a maf
>>>>unless I was wanted to run right at stoich or leaner in a gas mileage
>>>>attempt.  The map is an easier install and works fine, GM has used 'em
>>>>for years but in the end fleet gas mileage is important so the switch
>>>>will (has?) occur(ed) because if you want super control over your
>>>>mixture a maf will work better.  Yes, a maf is more restrictive but is
>>>>the difference significant?  A common choice of maf in custom
>>>>applications is the one from a 5.0L mustang as it has a bigger bore and
>>>>will flow more air and is readily and cheaply available.  I think the hp
>>>>limit of that maf is about 500 or so hp so if less than that I think it
>>>>would be a good choice.
>>>>
>>>>But then again, I am no car expert,
>>>>
>>>>Rick frey
>>>>
>>>>      
>>>>
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Diy_efi mailing list
>Diy_efi at diy-efi.org
>http://lists.diy-efi.org/mailman/listinfo/diy_efi
>  
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.diy-efi.org/pipermail/diy_efi/attachments/20060118/9efbc6fd/attachment.html