Commanded AFR ≠ {B3601}

[Steve Bryant]

I have a related question about {B3601} values. Some stock tunes use 14.63 and some use 14.68. Why the difference? Most truck tunes use 14.68 and most Car tunes use 14.63. However, if you'll look at the attached image from a 2002 ZO6 Corvette (downloaded from HoldenCrazy.com), it's 14.68.

[Steve Bryant]

TTT, I'm still curious. Does anyone have an idea about the 14.68 versus 14.63 that I posed above?

Thanks,

Steve

[WeathermanShawn]

Steve:

I caroused the Internet for about an hour after you posted your question. I was curious too.

I could not find a definitive answer. You had some difference with emission qualifications that year..No EGR, Corvette-pup cats were moved..but no real answer.

Its interesting looking at a 2002 Camaro vs 2000 Corvette ZO6. You will see subtle differences in O2 switch-points and Commanded fuel. Essentially everything is a little 'leaner' in the ZO6 vs Camaro..

Whether that was an EPA difference or the ZO6 H/C combo..it would be nice to know.

So, I could not find any definite information either. But, I have noticed the same thing. Perhaps one of our GM engineers can help us out.

[mr.prick]

Maybe because the fbody and ybody are supposed to use 93 octane
and trucks use 87 octane.

It doesn't matter what {B3601} is, all it does is set an AFR value to EQ1.
As far as the PCM is concerned it only knows EQ.

{B3601} should match your WBO2's Stoich AFR if you are using AFR & BEN as a tuning reference.
See this thread.

[TFZ_Z06]

TTT, I'm still curious. Does anyone have an idea about the 14.68 versus 14.63 that I posed above?

Thanks,

Steve

Just a guess, but in 2004, the Very Low Emissions standard was phased in. Some cars already had this status and I believe the 2002 Z06 was one of them.
Maybe this leaner mix was part of meeting that requirement??

[mr.prick]

Lean AFR=higher emissions
One of the reasons we don't have lean cruise in the US.

[joecar]

I have a related question about {B3601} values. Some stock tunes use 14.63 and some use 14.68. Why the difference? Most truck tunes use 14.68 and most Car tunes use 14.63. However, if you'll look at the attached image from a 2002 ZO6 Corvette (downloaded from HoldenCrazy.com), it's 14.68.

I have been curious about this for a long time and have never found an answer...

[joecar]

Lean AFR=higher emissions
One of the reasons we don't have lean cruise in the US.

More specifically: leaner AFR typically means higher NOx emissions and lower HC/CO emissions...

The EPA is willing to raise HC/CO levels a little to keep NOx levels low.

[Steve Bryant]

Thanks for the responses guys. Most citations of AFR for gasoline/petrol round to 14.7:1. It appears to me that {B3601} as well as some parameters like O2 Switch Points are trying to model Stoic for the PCM to properly reflect the O2 sensors so that various AFR/Lambda/EQ values are in harmony with the O2 sensor. It's always been a point of confusion for me and evidently for others too.

Thanks,

Steve

[TFZ_Z06]

Lean AFR=higher emissions
One of the reasons we don't have lean cruise in the US.

leaner mixtures increase gas mileage. As you approach stoich, the cats are supposed to work their best. Who said GM creates cars to reduce greenhouse gases? Are we trying to use less fossil fuels??