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View Full Version : High-flow cat effecting AFR's?

redline
11-11-2007, 12:35 PM
Is their a rule of thumb on how much a HFC will effect AFR's measured at the muffler. I have searched around and found nothing solid. Maybe the tuners here can shine some light on this for me. I don't have a bung for my WB yet and would like to reference my dyno sheet.
SovXietday
11-11-2007, 12:58 PM
Put your bung BEFORE the cat. It should be within 10-18" after the turbine.

I don't believe that the cat will make a difference in your AFR readings, as the oxygen sensor reads just that, oxygen. However, you want to place your oxygen sensor in the downpipe for most responsive readings.
redline
11-11-2007, 01:13 PM
Put your bung BEFORE the cat. It should be within 10-18" after the turbine.

I don't believe that the cat will make a difference in your AFR readings, as the oxygen sensor reads just that, oxygen. However, you want to place your oxygen sensor in the downpipe for most responsive readings.

I know this, I was asking what the Dyno sniffer was seeing was effected by my HFC, and if thier is a calculation to see what my true AFR's are.
redline
11-12-2007, 01:22 AM
Ok I just did a tone of searching on this and found that AFR's after your cat will be around .4 to .7 leaner than before your Cat. So a 12.0 reading on a tailpipe sniffer would actually be around 11.3 to 11.6 AFR. Anyone varify this?
SovXietday
11-12-2007, 12:18 PM
I know this, I was asking what the Dyno sniffer was seeing was effected by my HFC, and if thier is a calculation to see what my true AFR's are.

Ah ok. I don't have any experience with a post cat wideband so I couldn't tell you for sure.

Try PMing one of the vendors who have a dyno.:wink: