I know the use of an A/F meter(while dyno'ing) after a high flow cat is unreliable. And I assume using an open 3" exhaust w/ A/F meter at outlet is like having an A/F meter/reader in DP(ie pretty acurate readings). So, should it mater if I have a MP but say w/ a semi-restrictive CB? Will this affect A/F radings after the CB?
I have 3"MP w/ N1 duals now. Too loud. So should I dyno tune it properly now w/o restriction, then add CB, or can I wait until I get a more restrictive CB and still dyno w/ A/F meter getting proper readings?

Steve

 

Someone correct me if I'm wrong, but the reason you get incorrect readings after a cat is because the exhaust goes through the catalyst and is changed... therefore hosing up the A/F. I don't see any catback giving you a bad reading as long as there is no cat in the picture.

But, we all know the best place to put an o2 sensor is after the motor and before the turbo... anything else will get you less accurate readings... how much less accurate? Who knows... ask the owl in the tootsie roll commercial, he might.

 

Thanks, thats whay I thought.
Any idea which way A/F readings might be wrong(too rich or too lean)? If they are wrong, reading after the exhaust. It does not seem they would be too far off, but maybe alittle, now which way? Anybody know where that owl is, I think he might have passed away.

 

You sure about this? Won't the heat kill the sensor if it's before the turbo? I've herd that you want to place your WB sensor at the end of the DP or in the MP.

 

Narrow-band sensors (like the stock one or most of the A/F gauges you see) are only accurate at 14.7:1, so they aren't much use in tuning. They can tell you if you are lean or rich, but not by how much. Since you need to be a specific amount of rich, the narrow-band sensor is of little use no matter where you put it.

For accurate readings, you need a wide-band sensor like one of these:
http://www.techedge.com.au/vehicle/wbo2/default.htm
http://www.fjoinc.com/automotive/WBO2details.htm
http://www.rx7.com/cgi-local/3catalog.cgi?cat=12&part=6 (Pro Race setup)

-Max