ox sensor on sequential efi,high overlap cam....

[Bruce Plecan]

-----Original Message-----
From: Jemison Richard <JemisonR at tce.com>
To: 'diy_efi at efi332.eng.ohio-state.edu' <diy_efi at efi332.eng.ohio-state.edu>
Date: Wednesday, November 25, 1998 8:49 AM
Subject: RE: ox sensor on sequential efi,high overlap cam....

I maybe wrong here, but I've seen data logging showing what appears to be
the O2 responding to individual cylinder firings on a v-6 at 5,600rpm.  The
O2 still looks to be reading the exhaust pulses as they pass by the sensor
very well.  What happens between exhaust pulses would have little effect on
the
max O2 voltage.  Accuracy would be more a matter of the response time of the
O2 your working with.
  While I've never dealt with a realllllyyyyyy large cam with EFI, most of
the
headaches I've had are at idle, where the big cam bounces the MAP all over
the place.  I've heard rumors of cures by changing the idle MAP filtering,
but
have no first hand experience with that.
Bruce


>Wow,  if this isn't an opportunity to make a fool of myself I don't know
>what is.  Overlap is introduced by the cam designer to improve scavenging
of
>the cylinder and maximize fresh charge (new fuel / air) into the cylinder.
>To do this, the concept of overlap sacrifices fuel economy and an orderly
>intake/exhaust processing - rather muddling both processes together.  The
>idea works generally in a narrow rpm band (the more scavenging, the
narrower
>the band - thought this is also influenced by valve lift and assymetrical
>cam lobes, etc).  BTW, this can be fine tuned with intake and exhaust
>lengths (that's another story).
>
>The point of all this (and I'm very new to efi so take this for whatever
you
>feel it's worth); but from a newbie's point of view, O2 sensing
specifically
>and air/fuel measurement in general are pretty much worthless in this
>situation just because of the lack of process (intake/exhaust cycle)
>control.  Everything is sort of happening at once, so trying to "tune" the
>mixture based on a test sample of burnt fuel along with some fresh charge
>seems pretty worthless.  This is why those ultra simple constant flow
>injection setups worked so good!  FWIW, carbs also have some problems with
>cam profiles like this.
>
>Actually, might be worth the effort to forget the sequential efi (unless
you
>want to impress everyone in the staging area with your flawless idle
>quality) and just batch it (I just found out about this and it has changed
>my whole outlook on efi!).   You have that much cam, you're not idling
>anyway!
>
>rick
>
>> -----Original Message-----
>> From: Espen Hilde [SMTP:mwichstr at online.no]
>> Sent: Wednesday, November 25, 1998 3:08 AM
>> To: diy_efi at efi332.eng.ohio-state.edu
>> Subject: ox sensor on sequential efi,high overlap cam....
>>
>> I have a question that I have been thinking about lately.
>> In a engine with high overlap cam and sequential efi,how to measure air
>> fuel ratio?
>> At certain points in the rpm scale the engine is scavenging air right
>> trough the engine.(I presume)
>> At overlap.The sequential efi will not inject fuel to this amount of
>> air.(not supposed to....)
>> The result as I see it,is that air is pulled trough to the exhaust
>> system.The ox sensor (if it sensors 02)
>> will say this is a lean condition.
>> Am I worthy of a coned shaped hat?
>> Espen Hilde
>