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Discussion Starter · #1 ·
Has anyone compared the a/f readings measuring from a bung welded before the cats oppossed to the end of the tailpipe on a catted car?

Most dynos with a/f insert a probe into the tailpipe. how accurate the a/f could be going through the cats?

thanks, Marlon
 

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When I tune I prefer a bung welded right after the header in the cat pipe. This takes out many variables: cats. leak in exhaust, poorly maintained 02 on dyno( dirty filters, pluged tube etc.) At alot of dynos the do so many cars with leaded race fuel and this also deteriorates the w/b 02 sensor. Plus I feel that 7 & 8 are the cylinders that go lean first so the drivers side is where I like the bung. Plus you can drive down the road and check the a/f. To me this is very important because at wot in 4th gear you are only in so many load tables. On the road I can check to see if the car goes lean at tip in, and in 6th gear where it will go in the highest load tables at low rpms. I can also datalog the a/f to see the curve going through every gear and adjust a/f at cruise for some milage increase. Hope I could help bud.

Rick
 

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I found the difference is about .06-1.0 from being in the bung compaired to the tail pipe. They all will vary. Nitro :)
 

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Got to be lean I would think.
 

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DD2000GT said:
Got to be lean I would think.
Thats what I was thinking......so.....in other words if you are running at 11.6 at the tailpipe......you may only be running 10.6-11 at a welded in bung.

Anyone with me on this??
 
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