Just double checking here.

The O2 sensor voltage should be between 890-910mv for a naturally aspirated car correct?

 

ttt

 

That is a pretty narrow range, but sounds close to what I have seen from my NA car. Perhaps that is the optimum range. I'm sure Fred or others would know.

 

I'm surprised you would ask that question after all the posts that have explained why the OEM narrow-band O2 sensors are NOT accurate at the A/F ratios you need at WOT. The sensors are extremely sensitive to operating temperature once you get richer than about 14.5:1, and a very tiny change in operating temperature will cause more of a mV change that a major change in A/F ratio.

In a stock/bolt-on engine, I seemed to get the best results at 880mV. But if you are running long tubes, with relocated O2 sensors further from the engine, the sensors are going to run at cooler temps and produce different results. I remember someone, maybe it was Keith at WS6.com who liked 820mV, which seems way low to me, but worked for him. There are also problems with some scanners that cause inconsistent mV readings... the HPP scan cartridge was notorious for showing 800mV readings for cars that would show 900mV on a more reliable scanner.

Point is stock O2 sensors aren't reliable.... get it tuned on a dyno, with a wide-band analyzer. Anything else is just guessing. You put a lot of $$$ into the engine... why not finish the job with a "professional" tune..... .

 

What fred said is correct, but just to throw some numbers out there, mine with longtubes liked 02s in the 870ish range. Also you will more than likely that the two sensors will read slightly differently.

To correct for this i wrote a basic program that averaged the o2 readings at WOT, and then graphed them vs RPM. Made tuning at the strip cake.

 

Please don't use O2 sensor voltage at WOT to get any indication of a/f ratio.
I've had a couple of cars on the dyno in the last 2 weeks, and they both seemed to make good power at 13:1. If I added any fuel the curves wouldn't move and the car wouldn't pick up anything torque or horsepower wise.
Now after looking at the datalogs on those 13:1 pulls, BOTH cars have O2's in the 940-960 range.
So I went back and looked at some of the earlier pulls that were made when the car was much leaner. If I remember right a/f ratio was around 14.5:1 and bouncing around quite a bit.....looking at the datalogs for both cars the O2 voltages were between 880-900.
SO, please don't use O2 voltage for a reference....
On both of these cars 880 was way to lean for me to be comfortable.