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

Jemison Richard JemisonR at tce.com
Wed Nov 25 13:14:46 GMT 1998


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 



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