[Diy_efi] pic based afm -> maf conversion

Wed Jan 18 17:38:25 UTC 2006

MAF has 2 other disadvantages.  

One is sensitivity to pre-MAF intake modifications.  This changes the
flow profile (flow vs. position within the pipe).  Given your engine is
consuming the exact same, if the flow profile changes, the MAF reading
does as well.  Obviously, pre-MAF turbulence will heavily effect this
sensor.  

The other drawback is with long-duration cams, reversion means the same
chunk of air passes through the MAF twice and gets measured twice, which
obviously throws the readings WAY off.  

MAP systems can have issues with long-duration cams as well, but that
problem is fixed with a vacuum manifold.  

  _____  

From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
On Behalf Of Tom Visel
Sent: Wednesday, January 18, 2006 10:25 AM
To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] pic based afm -> maf conversion

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

		are confidential and may also be privileged. If you are
not the intended
		recipient, please notify the sender immediately and do
not disclose the
		contents to any other person, use it for any purpose, or
store or copy
		the information in any medium.  Thank you.

			_______________________________________________
			Diy_efi mailing list
			Diy_efi at diy-efi.org

http://lists.diy-efi.org/mailman/listinfo/diy_efi

		_______________________________________________
		Diy_efi mailing list
		Diy_efi at diy-efi.org
		http://lists.diy-efi.org/mailman/listinfo/diy_efi

		_______________________________________________
		Diy_efi mailing list
		Diy_efi at diy-efi.org
		http://lists.diy-efi.org/mailman/listinfo/diy_efi

  _____  

	_______________________________________________
	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/c1a1f5d1/attachment.html 