efi conversion - o2 sensor question

[zane]

I just ordered a set of headers and had them weld in a bung for a wide band o2 sensor. I thought it strange that they welded the bung into the number 2 pipe only 3" downstream from the exhaust port. Is there a minimum distance that the o2 sensor should be placed downstream? I posed the same question over on the megasquirt forum and can't seem to get an answer.

[Mike87]

That sounds like it would be for an exhaust temperature guage rather than an O2 sensor. Typically an O2 sensor would be welded into the collector where it would get exhaust from all cylinders.

[zane]

That's what I thought; down at the collector.

[TobyB]

(at least for VW!)

I'm using a VW sensor, and it's max temp is 900f- you'll have 1400- 1600f at the flange.

I actually have my sensor in the pipe after the headers- so far, I've had to replace it once, but I'm running leaded fuel... It works fine until it gets contaminated- I was saving the contaminated one to run in the street car to see if it would recover. Just out of curiousity...

t

[BAhyow02]

Zane,

Yeah Toby is correct. Way too close for the 02 sensor. It will overtemp and then either shutdown or give erronous readings (depending on the electronics reading the 02 sensor).

The s14/e30 m3 guys run the sensor down at the collector as far away as they can get it before the cats. Some still have minor overtemp issues but that is with a 320+ hp gruppeA/rally engine on the track.

Toby, geez if you are at 1400 to 1600 F EGT that's pretty extreme--what's your A/F?. The engines I've seen will only tolerate 1550+ for a few seconds before parts start failing. Maybe you could use a tad more timing? Are you running AV gas...that stuff has a really slow burn which could explain the problems.

At work we used to run AVgas (110 LL) in a turbo engine, then we switched to race gas and EGT's dropped significantly with less timing needed. That and parts started lasting longer due to the lower EGT temps.

Goodluck,

Bernard