Topic: O2 sensor

[Don R]

Has anyone tried an O2 sensor on a sohc? I just installed one on my dragster V8 and am amazed to see the wide swings from a good ratio to way lean as the engine idles. I can see every time the cyl fires and then goes extremely lean as air rushes back into the tube. There is obviously much reversion even 12" away from the cylinder head on a tuned header with step tubing sizes and a merge collector. I can't wait until there is time to insert it in the bike header. (After we do some racing)

[turboguzzi]

not sure if it answers your question but came across quite a few articles that say that O2 sensors are quite irrelevant in tuning slide carbs due to these immense variations in mixture.

A pretty good tuner friend, builder of some championship winning bikes here, welded a connector to one of th exhaust pipes and goes by EGT (exhaust gas temperature), seemingly much more relevant than a lambda prove to our type of enigne/carbs.

my 0.02

TG   

[Bamboozler]

Don R, wondering if you are using a narrow band O2 setup (0-1v signal) or a wide band (0-5v signal) in your dragster? 

I can see extreme swings with the narrow band.  Works good enough for a auto's fuel computer to determine stoic during closed loop operation, but not very accurate for a tuning tool when a expensive motor could be on the line. A wide band would open up the data point range and smooth out the erratic swings. 

For what its worth I have a wide band on my CB that's measuring all 4 pipes and the resolutions is pretty good.  An example, when wide open throttle using #120 main jets I was seeing ~12.3-13.0:1 A/F ratios.  Changing the #120s out for #130s moved that down to ~10.2-11.0:1 (depending on where the boost is at). Reasonably good resolution and very repeatable with the stated numbers always coming up at the same speed/rpm/boost..  Steady idle bounces around a range of 1/4 to 3/4 of a point with the gauge scale that displays 10 points (8-18:1).  Not a end all have to have tool, but a seems to work well to tell you where your fuel changes are going and tune sits.