Where would you say the optimum placement for my O2 sensor would be? 4” exhaust routed out the fender. Can you be too close to the the turbo? I’ve heard you don’t want it to close to the end due to air scavenging and throwing your reading off. #ad

 

Usually mfg calls for something like 6-8" after the collector (turbo in your case) but not closer than 18" to the exit. Your wideband should have some documentation about it. You might get away with it being a little closer to the turbo, it ought to homogenize things a bit.

 

is that a fender exit exhaust? Maybe 3-4” back from the first bend after the turbo

 

It’s a Bosch sensor that came with my holley terminator x kit, I’ll look into if they mention anything.

Yes it’s a fender exit setup.

 

It’s 28.5” total length from the turbo flange. The blue circle is 10” from the turbo. Kind of thinking of placing it there.

Next question, can the sensor be at a 45° angle or must it be 90° to the flow? #ad

 

Well that’s where it’s going haha. #ad

 

The danger of being close to the turbine is temperature. When typical in-car widebands get hot, they start to read rich. By 1600*F it could say 11.5:1 even if the true a/f is 16:1. Its a chicken and egg situation where only lean engines run hot enough at full power to overheat the wideband so you get both worst possible outcomes at the same time, operator thinks its rich engine is really lean, toasted chicken and egg.

Conversely near the exit they will not function correctly.
Usually we take it at least 15-18" From the turbine.
The position needs to be such that water does not accumulate, mostly pointed down is ideal. Instructions show angle of mounting possibility but the more down in gravity the better.

 

No being towards the end of the pipe, say if I moved mine closer to the fender and only 10” from the end. Would this only operate incorrectly at part throttle and cruising due to fresh air being introduced? But under WOT it would operate fine as the amount of flow from the turbo is. Or going to let any fresh and air back feed into the exhaust. Thoughts on this?

If this is true, I understand the problem with mounting it towards the exit, but in my case going with a blow through carb…wouldn’t only WOT be my main concern reading correctly?

 

Well that is a difficult question to guess because turbines tend to smooth out the exhaust pulses of an engine but they do not completely eliminate them. Its not like a hose jet of water laminar flow, it can be chaotic/turbulent and really mixing up with outside air in the last distance of the exit.

There is always some pulling air into the exhaust, it could be farther up than we realize and it could adversely influence your readings. You are correct at WOT it SHOULD be less of an issue and if you don't plan to do any part throttle tuning it would just make the wideband useless at part throttle and you unable to really tell if the engine is tuned properly or not I guess. Does that make a difference to you? To me, it would. I don't want to pull out spark plugs to know whether an engine is tuned or not, I just wana look at the wideband and leave the plugs alone.

In the picture it looks like you did the best you could, its probably fine if the EGT doesn't get crazy. Like using alcohol fuel 1/4 mile at a time is prob fine. Gasoline things get a bit hotter. In this type of situation the best thing to do is
1. compare results with dynometer wideband at the same time compare them, dyno setup will keep the gas much cooler and sample it more effectively
2. when tuning use circumstances that guarantee the EGT hasn't skyrocketed yet. Like making wot pulls on a recently warmed up engine and be more wary as the day goes on temps get higher and higher, give the engine a rest
Worst scenario is, If you are doing a extended wot pull on a hot engine and notice the a/f starts climbing into the 12's and then suddenly drops into the 11's... watch the f out it just leaned out and got hot enough to !@#$% the sensor

 

That’s good advice. As I won’t be chasing big boost or power levels anytime soon with this engine it is the end goal for it. I will get some dyno time once I feel like I have tuned it the best I can on the street. It will be good to compete afr readings then. For know I won’t be doing any longer pulls on the street than I’d see in a 1/4 mile, but like you mentioned cruising around for an hour on a heat soaked setup and doing a 2-3 gear pull is different than a just warmed up engine doing a pull.
Just out of curiosity, what are the temp limits of these sensors? Or is that manufacturer specific? It’s a Bosch sensor if that helps. Mainly curious if checking that location with a pyrometer would help worst case.

 

It is based on the sensor. Widebands are actually narrowbands with a pump. The cheap in-car units are probably far more susceptible to deviation than professional gas analyzer.

The document or instructions may say somewhere what the temperature ranges are, personally I've had one go crazy rich around 1600*F the a/f on the dyno was 15:1 and the wideband showing 11.5:1 in my datalog.

 

I would of put it in the same spot you did. I didnt have much overall length on my fender exit setup either and it was fine.