AFR's with CAT
 

Hi all, a friend of mine wants me to check the fueling on his subaru, the car is stock but has just been rebuilt.

my wideband is used with a tailpipe sniffer, so am wondering how the stock catalytic convertor affect afr readings?

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Come on man you know its going to look crazy lean out the tail pipe with a cat on it.. Slap a test pipe on it or your not going to get the correct readings.

I dont know what the readings are going to be like.....hence the question.

have heard a tuner here in the uk say it was about 0.6 (afr) different.........don't know if that was a constant though through the rev range.


.....pain in the arris to put a decat (test pipe) on the scooby downpipe....specially with rusted turbo bolts.
(but surely this also wouldn't give a correct reading as it is being run with the restrictive cat)

Its going to be consistently high if the cat is functioning.

If its a major problem maybe goto an exhaust shop and have them weld in a bung?

Sorry to hear its a scooby i know those exhausts can be a bugger! What kind of scooby is it?

the scoob is a stock '98 uk wagon (bar a fuel reg), car is running fine at the moment after the rebuild but was wondering if I could check the fuelling at the tailpipe without too many issues.

I was wondering if anyone has done any logs with a wideband pre and post cat, is there a constant calculation I could use to get a semi-accurate reading.

don't really know how a cat works, will readings vary from one cat to another?

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just found this on google

http://www.innovatemotorsports.com/f...ad.php?p=12691

I think you would have to many variables to use a constant.

A cats efficiency can change over time and I believe that would mess up your readings as well.

Have a bung welded in pre cat, take it to the dyno and when done, use a bolt to block it up.

precat would be right next to the turbo, isn't too much heat bad for the o2 sensor.

....will be checking car on the road (not a fan of rolling roads/dynos)

You'll need to use a heatsink. Innovate includes super simple instructions in their manual which you can get online.