Just built a 408 and had tuned by a local tuner. Afterwards I installed a new autometer wideband and at WOT its reading about 13.4. Is that too lean? I know they where measuring a/f at the tailpipe, and was tuned at about 12.9. Would there be that much of a difference from the header to the tailpipe??? Any help please...

 

There can be, but in my experience the results are usually opposite... You may wanna give em a call, a change like this is simple and takes little time, they will prolly cconsider it a touchup if it was recent.

 

In addition to what Frost said...I take it you don't have cats? Furthermore, WB's are very picky about power and ground. Your WB could be right, or wrong. I'd take the setup back to the shop and ask them to help you verify that your setup (the WB02) is in agreement with their setup and vice versa. In absence of the catylic action, the WB's (properly setup) should be really close, if not identical.

 

Its common to be leaner by 0.5 on the street than dyno. So for you 12.9 on dyno is the same as 13.4 on the street/strip - but the engine might not be happy with 13.4 - the answer is that it needs to be richened up to compensate for the shift.