Do headers lean out the A/F Ratio too much?

I found a short write-up on Mopar Performance's website at the link below which explains that the increased scavenging abilites of headers can possibly lean the A/F ratio out too greatly on fuel injected engines.

http://www.mopar.com/muscle/tech1003.htm

Is this the case with RENIX and HO 4.0s? Would the installation of a long tube header (Borla or Pace Setter) require the installation of an adjustable MAP sensor or something else which could compensate for the headers increased scavenging ability and introduce more fuel to maintain a correct A/F ratio?

To play devils advocate - wouldn't increased scavenging in the exhaust result in slightly lower intake manifold pressure that would be sensed by the MAP and communicated to the ECU?

In most cases, any modification that increases power output means its gonna burn more air and fuel, and on a map style efi system in WOT they don't use the o2 sensor for fuel mixture correction, so yes there is the potential for air/fuel ratios to be leaner, and potentially too lean which increases the chance of pre-ignition/knock/detonation (whichever you'd like to call it today).

That said, you can usually get away with a header and exhaust on a Jeep without worrying too much about it.

You could get yourself a piggyback fuel computer, bigger injectors, and a wideband oxygen sensor/gauge and try to get into manually tuning your engine, but you're really starting to get a little over most people's realm of ability.

I'd think you'd only really see a LEAN condition if you start moving more air than the OEM fuel injectors can support.

Yes, the HEGO is ignored at WOT, and the system will usually guess for a "best power" mix (~13.0:1? I'd have to check) and the HEGO is ignored at startup for "Open Loop" operation. However, how many of us run for a long time at WOT? With the HEGO in circuit and in "Closed Loop" operation, the system should be able to compensate for the increased air throughput of the engine (caused by the improved scavenging of the header.)

Didn't we just go over this in PMs? You're getting me thinking - I've got to build that run stand I've been thinking about... It would be interesting to compare various headers with an eye toward this (and other!) facts...

5-90 said:

"best power" mix (~13.0:1? I'd have to check)

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correct.

WheelinJR said:

correct.

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I knew it was down around there, I just couldn't recall the specific number offhand. Don't suppose you know, do you?:eyes:

13:1 - best power
14.7:1 - best fuel efficiency
http://books.google.com/books?id=ze_w0i3xZmAC - best possible learning tool for understanding EFI (well, one of the best)

WheelinJR said:

13:1 - best power
14.7:1 - best fuel efficiency
http://books.google.com/books?id=ze_w0i3xZmAC - best possible learning tool for understanding EFI (well, one of the best)

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I knew I could Google it. I've also got the numbers in about six books on engine theory around here... I just didn't feel like digging any of them out at the moment, and I didn't want to switch gears on the searches I'm running...