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This is a breakdown of the A/F ratios to millivolts for standard O2 sensors provided by Matt.

"Jeff Meager wrote:

I have a Westech A/F ratio guage as used in Aircraft etc....which shows you very roughly - but is dampened....the ratio's..... according to the guage, 750 upwards is around 12.5 heading towards 12.0:1.  I have all my maps running 750-800mv and have no detonation etc.... pulls well and according to the westech guage - it is running around 12.5 - 12.0:1 AF.  Yes I know that these sensors are very sus, but it has worked very well for tuning over the past three months.....  You can see when you do, and should get detonation from lean.....if you head down into the 13:1 range....  Jeff


Here is a rough guide to what the mV reading will be for the Haltech (NTK/NGK) 4-wire sensor, as well as most OEM 1V sensors.   I have found these over the years from using good AF Meters , and also what the Engine Data reads after the tune.

500mV -   15.0:1
600mV -   14.5:1
700mV -   14.0:1
830mV -   13.5:1
900mV -   12.9:1
925mV -   12.7:1
950mV -   12.5:1

This is only a rough guide but should get you close.  It is by no means an accurate way to tune your car as your sensor may read slightly different.     Generally most engines develop best torque at around 12.6:1 - 12.8:1 , but for economy and emissions the engine may be run leaner.
--
Matt
The HITman - Haltech Injection Tuning "