O/2 Sensor location

[Tom Goldman]

Kris , you are correct .
you can smooth out the O2 graph so it makes sense on the time line of the run.
Having read and interperted data recordings made for repairs on street vehicles at the JEEP dealership I worked for made it easier for me to use the RacePak O2 graph, but you can get a lot of data with a very few runs, and lean to interpert it .

[Signman]

It probably is better on a carburetor car to have the O2 in the collector if only one. Intake manifold can make fuel distribution uneven cylinder to cylinder. If in the collector you need to have an extension with the O2 as close to the convergence of the four primary as possible. One in each primary within 20 inches of the exhaust valve is best. In fuel injected cars because fuel distribution is pretty equal based on the location of injectors one in primary tube can work well. It does for me.

Understand that everyone has their own opinion /experience and different O2 locations work good or not so with varying assemblies. What is important is that what ever data reviewed is understood for what it really is.

O2 in the primary tube will see less fresh air than when installed in the collector. Am convinced with the cams we run O2 will see some fresh air no matter where located and more so in the collector.

In the collector AF will read more lean than if in primary tube. Check plugs and exhaust ports / headers. They don't lie. Be careful when helpful people say it should be this or that AF. My last motor was lifting the head trying to run it as lean as was being advised. They had O2 in collector while mine was in primary.

If you would like to get in the ballpark quickly spend a day on a chassis dyno with a good tuner. Review sheets from your the best runs. Those AF numbers are real for your assembly. Maintain and test variations on those.

In Div 1 there is a good tuner in Danbury CT.

Good Luck and Have Fun!

[MOTORSPORTS Innovations]

Lot of good info here.

I recommend the bung in a primary tube AND a couple of bungs elsewhere. Like Tom says once you find a primary that "speaks for the whole engine" go with that.

I have had a lot of different O2's on my car (including 2 different brands in the same tube) and really like the Racepak. Having said that, any of these tools should be balanced with what the time slip says and your gut or a second source of info like plugs etc.

To get the average AF with Racepak data link:

1. activate the AF channel
2. select the AF channel in the file/grid box at the top of the graph area.
3. place the cursor on the start point and left click, then push the [ key on the keyboard
4. place the cursor on the end point of the time of interest and left click, then push the ] key on the key board

other help & tips: http://www.motorsportsinnovations.co...-help-tips.htm

[older racer]

hi, we ran aO2 sensor in collector, reading was within .3 whole run. I also, look up in collector with a light, if its white, =lean, black =rich, dark grey,= about right .

[art leong]

I have my O2 about 8 inches from the end of the collector. In order to get a proper reading at idle I have to put on a 24 inch extension made from flex pipe.
I can't reley on the O2 reading below 4,000 rpms without the extension on. After 4,000 or so it reads fine.
One thing I have noticed though is that the O2 reading is higher (leaner) in first and second gear, than in high at the same rpm's.
I've been tuning off of the high gear readings. And it seems to work.

[Alan Roehrich]

We locate ours right after or right before the minor diameter in the merge, preferably before, so it is as far from the end of the collector as possible. If not using a merge, 4-6" from the ends of the primaries. Also, between 10 and 2 o'clock, if possible, so as to prevent moisture from condensing in the sensor when it is off. The sensors aren't real happy lighting off with water in them. You may see some fluctuation at idle, or rolling along in the pits or staging lanes, due to fresh air being drawn back into the collector at low RPM, but when it really matters, going down the track, it will be fine.

[art leong]

Originally Posted by A56

I put them anywhere between 10" - 14" out on the primary tubes, try to find a good average for all eight and stick with that # of inches away from port. If you have a step in that area, put them right after the step, this helps because you just added some area to the primary tube, and if you do it just after a step the area change isnt as critical. Make sure you use a long O2 weldment, so the O2 dosent protrude into the tube excessively. In the collector I put them in the choke if the choke isnt excessively small, or just before the choke as to not change the area but get all the gasses. Though lots of people say not to put them in the collector, I dont agree, if your collector isnt short, they work fine there. I have not tried them on a straight collector, but can only assume you will get outside air at low RPM.

Mark Lelchook
F/SA

Mine shows excessively lean at low rpms. I once tried to tune the idle before I knew about the extension trick. And it was smoking black and still showing lean.