[Diy_efi] Intake manifold flow testing

Dave Dahlgren ddahlgren at snet.net
Wed Feb 12 11:23:12 GMT 2003


The whole point about logging it is to see if the problem is real or imagined..
A lot of tribal knowledge is just that chicken bones and voodoo....
Dave

Grant Beaty wrote:
> 
> >From the things I've seen with my own car and read about others, 35C is
> about 1 entire a/f point (ie 11:1 to 12:1) if everything else is equal. Of
> course, everything else is rarely equal (especially timing w/ active knock
> control), so YMMV.
> 
> Grant
> 
> ----- Original Message -----
> From: "Geddes, Brian J" <brian.j.geddes at intel.com>
> To: "List for general do-it-yourself EFI talk" <diy_efi at diy-efi.org>
> Sent: Tuesday, February 11, 2003 6:17 PM
> Subject: RE: [Diy_efi] Intake manifold flow testing
> 
> How different would the A/F ratio in the cylinders need to be in order to
> create a 100F difference in EGTs?  Are we talking about a tenth of a point,
> or a point, or a couple points?  My concern is the EGT may be too coarse a
> measurement.
> 
> - Brian
> 
> >
> > I would never use it for any kind of absolute numbers as it
> > is as much timing
> > related as anything else. With that said you are only looking for a
> > differential.. If the timing is the same in all cylinders and
> > the fuel is the
> > same then the egt ought to be as well if you allow a little
> > 'windage' for
> > cooling system issues. If they are different then I would bet
> > the only thing
> > that is different is the airflow.. It might be worth a little
> > fuel tweaking to
> > even them up if they are a lot different.. Over 100 deg F
> > would be my threshold
> > to play a little.
> > Dave
> > "Geddes, Brian J" wrote:
> > >
> > > Is there a close enough correlation between EGT and A/F to
> > use EGT to estimate the relative airflow differences?  I
> > thought that the EGT-A/F connection wasn't very exact...but
> > I'm certainly no expert.
> > >
> > > - Brian
> > >
> > > > -----Original Message-----
> > > > From: Dave Dahlgren [mailto:ddahlgren at snet.net]
> > > > Sent: Tuesday, February 11, 2003 12:15 PM
> > > > To: List for general do-it-yourself EFI talk
> > > > Subject: Re: [Diy_efi] Intake manifold flow testing
> > > >
> > > >
> > > > The sad part about this problem is that it most likely
> > > > changes with rpm as well
> > > > that is to say they can move around. a rich one at 4500 might
> > > > be a lean one at
> > > > 6000.  You could probably verify they stay the same by using
> > > > some egt probes and
> > > > data logging them along with rpm map and tps..Above all i
> > > > think i would only
> > > > want to add fuel.. Best idea is get a better intake manifold.
> > > > Dave
>


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