[Diy_efi] pic based afm -> maf conversion

Wed Jan 18 17:24:40 UTC 2006

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
>>
>>-----Original Message-----
>>From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
>>On Behalf Of Ashley Evans
>>Sent: Wednesday, January 18, 2006 10:26 AM
>>To: diy_efi at diy-efi.org
>>Subject: Re: [Diy_efi] pic based afm -> maf conversion
>>
>>Yes AFM is the flap device.
>>
>>It's not Airflow that's required anyway.  It's air mass.  I'll rephrase 
>>my question.
>>
>>Does anybody have any comments on the relative merits of MAF vs. MAP, 
>>given that calculation is required to generate the correct information 
>>for the ECU?
>>
>>Personally I would have thought that the calculation is prone to error 
>>and the MAF will give a more accurate reading.  Having said that, MAP 
>>will mean there's no restriction on the intake which would obviously be 
>>more efficient.
>>
>>But, I'm no car expert... hence my original question.
>>
>>Ashley
>>
>>
>>Steve Ravet wrote:
>>  
>>
>>> 
>>>
>>>
>>>________________________________
>>>
>>>	From: diy_efi-bounces at diy-efi.org
>>>[mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Ashley Evans
>>>	Sent: Wednesday, January 18, 2006 7:38 AM
>>>	To: diy_efi at diy-efi.org
>>>	Subject: Re: [Diy_efi] pic based afm -> maf conversion
>>>	
>>>	
>>>	It's 5 (or actually ~4.9)  at WOT.  This goes for the MAF and
>>>AFM.  What differs are the idle outputs and the voltage curve to WOT.
>>>	
>>>	I'll post full details here once I get an operational version.
>>>As I'm sure there are many system that could benefit from this kind of
>>>thing.
>>>	
>>>	Never really considered MAP.  I'm not planning on FI atm. and
>>>many others on the e30zone (or which I'm a member) have done MAF
>>>conversions costing upward of 800+ , I was sure that there was a
>>>    
>>>
>>cheaper
>>  
>>
>>>way.  I'm expecting my conversion to cost under 100.  50 or so for the
>>>MAF, and under 50 for the PIC.
>>>	
>>>	For my application I can't think of a reason to go for MAP.
>>>	
>>>	Do you guys have any comments as to the pros and cons of MAP/MAF
>>>?  For naturally aspirated.
>>>
>>>
>>>MAP and MAF aren't interchangeable like that.  MAP by itself doesn't
>>>give enough information to do fueling, it has to be combined with RPM
>>>    
>>>
>>at
>>  
>>
>>>least in order to calculate airflow.  MAF gives airflow directly and
>>>    
>>>
>>so
>>  
>>
>>>already has the RPM term in it.
>>>
>>>Is AFM the flapper door flow meter?
>>>
>>>--steve
>>>
>>>-- IMPORTANT NOTICE: The contents of this email and any attachments
>>>    
>>>
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>>  
>>
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>>
>>
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