Emission Target A/F?

[Eticket]

Hello,

With a catalytic converter installed:

When I tested my car in Texas last year on the emissions dyno, it barely did not pass the NOX measure. This is with a FAST system with cruising target A/F at 13.4 I believe.

Two years ago, I was using a stock ecm and it DID pass emissions.

I'm thinking of trying again with the FAST and Cat and setting the target A/F to 13.7? I've heard of our cars not running correctly with lean A/F's so I didn't want to hurt anything.

this is a 270" Champion headed stage motor....yada yada.

Thanks,
John Nguyen

 

[ijames]

You want the afr to be 14.7 with a catalytic converter. This will raise your coolant temp a few degrees over an afr of 13.4 but won't hurt anything.

 

[norbs]

well it might not run at 14.7 at idle so you may have to raise the idle rpm a bit. This chart might help you a bit. Keep in mind the chart is for NA applications

 

[Eticket]

Looks to me that to reduce NOX, the A/F should be in the 13.8-14.1 range?

 

[ijames]

Looks to me that to reduce NOX, the A/F should be in the 13.8-14.1 range?

As far as producing less NOx at the expense of slightly higher CO and HC, compared to 14.7, yes. However, the catalytic converter needs the afr to average 14.7 so it can efficiently handle all three.

 

[norbs]

Carl is correct the converter only has a very narrow band of operation to be efficient.