AFR's with CAT
Thread Starter
Evolving Member
Joined: Aug 2007
Posts: 104
Likes: 0
From: wales
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?
my wideband is used with a tailpipe sniffer, so am wondering how the stock catalytic convertor affect afr readings?
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.
Thread Starter
Evolving Member
Joined: Aug 2007
Posts: 104
Likes: 0
From: wales
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)
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)
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)
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)
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?
Thread Starter
Evolving Member
Joined: Aug 2007
Posts: 104
Likes: 0
From: wales
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?
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?
Thread Starter
Evolving Member
Joined: Aug 2007
Posts: 104
Likes: 0
From: wales
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.
