Wideband O2 Question

[nickpohlaandp]

I've used wideband O2 sensors many times in the past for tuning vehicles, and I'm about to do it again, but this vehicle is going to be a bit different in regard to exhaust setup. In all of the vehicles that I've done before, they have had a full exhaust system installed. This vehicle I'm about to start working with (1970 Cobra Torino 429) is getting a new set of long tube headers and the sensor will be mounted at the collector, same as all of the other vehicles I've done, but this one will NOT have any exhaust off of the end of the reducer... at least for a while. The owner want's to run open headers. I've already told him it's going to be obnoxiously loud and really have no benefit to do so, but I think the "obnoxiously loud" is something he wants... at least until he gets a ticket for it.

Without having any exhaust (well, maybe 3-4") aft of the wideband O2 sensor, will that throw off the readings? Should I get something like a 12" pipe just to put on the end of the collector or will it be fine as it? Thanks for your input.

[David Redszus]

Yes, it will. Any leakage of ambient air into the exhaust stream will affect the readings.
However, if you are only interested in relative readings, then it won't matter.

[adam728]

As said, you'll take in fresh air and skew readings if too close to the end of the pipe. I think the typical recommendation from wideband suppliers is 18-24" from the end of the exhaust. In our testing it's best to stay pipe diameter times 5 (or more) from the outlet on a single cylinder. More critical at lighter loads with less exhaust gas volume.

[nickpohlaandp]

This is kinda what I was thinking. In the past I've never been concerned about getting accurate readings with putting it at the collector because there'd be a complete exhaust system behind it. This nincompoop wants to have his car loud as hell, so I won't have that option. I'm thinking he doesn't know exactly how loud it's going to be though, so hopefully he'll rethink his decision once I fire it up for the first time.

[Rick Finsta]

Once you get above a certain RPM you'll see the reading stabilize. Basically once the flow is such that fresh air isn't getting back into the pipe. You should be able to see it in datalogs by making changes and then slowly revving the engine. Whatever RPM you see the changes consistently read (lean if you leaned it out, rich if you richened it) that's the point at which you can start trusting the sensor.

Scatterplots are nice for this, but not necessary.

Hope that helps.

[nickpohlaandp]

Once you get above a certain RPM you'll see the reading stabilize. Basically once the flow is such that fresh air isn't getting back into the pipe. You should be able to see it in datalogs by making changes and then slowly revving the engine. Whatever RPM you see the changes consistently read (lean if you leaned it out, rich if you richened it) that's the point at which you can start trusting the sensor.

Scatterplots are nice for this, but not necessary.

Hope that helps.

I figured it'd be ok for checking cruise and WOT, but getting idle isn't going to be very accurate. I'm just going to be tuning the new Holley that I'm putting on it, so it's not like I'm relying on it for fuel injection. I just prefer to use a wideband vs. checking plugs and guessing. That said, I'm more comfortable guessing with idle mixture than I am with WOT. I don't see the engine doing any damage to itself if its running a little fat or a little lean at idle.

[Belgian1979]

Maybe put some length of pipe on it so that it has volume behind the O2 sensor before it exits into the atmosphere. Remove the pipe when done.

[nickpohlaandp]

Maybe put some length of pipe on it so that it has volume behind the O2 sensor before it exits into the atmosphere. Remove the pipe when done.

That's what I was talking about, maybe putting a 12-18" piece of pipe from Auto Zone or something like that on the end of the collector. I'm not going to get too bent out of shape about it, this was just more of a curiosity thread, confirm what I suspected kinda thing. I'm hoping he hears it, get's his hardon, drives it for 5 minutes, and realizes that you can't drive a car around like that without begging for trouble.

[Belgian1979]

Maybe put some length of pipe on it so that it has volume behind the O2 sensor before it exits into the atmosphere. Remove the pipe when done.

That's what I was talking about, maybe putting a 12-18" piece of pipe from Auto Zone or something like that on the end of the collector. I'm not going to get too bent out of shape about it, this was just more of a curiosity thread, confirm what I suspected kinda thing. I'm hoping he hears it, get's his hardon, drives it for 5 minutes, and realizes that you can't drive a car around like that without begging for trouble.

I have a middle muffler and end muffler on my car (straight through types) and I even find it too loud at times. Can only imagine what a straight out the header system will create. Like you say a couple of minutes a hardon and then the fun is gone.

[turbo2256b]

Many builds will even run best with a collector extension. Many times in the 18" range give or take. Would get a long extension use some cheep paint to run a stripe down the extension then cut the pipe were it burns the paint first.

[nickpohlaandp]

Many builds will even run best with a collector extension. Many times in the 18" range give or take. Would get a long extension use some cheep paint to run a stripe down the extension then cut the pipe were it burns the paint first.

I've read about this in the past. What initially spurred my interest is when I was doing dome day-dreaming web-surfing looking at high dollar stuff that I'll never need and I noticed a lot of high end headers come with quick-interchange collectors (lengths, shapes, etc.). Pretty cool stuff once I started reading about it. This is so NOT the case with this car though. This car is just really a "daily driver" cool old 429 Torino. Personally I think it'll run better with a full exhaust, but if he wants to run it with open headers, then he can run it with open headers. I give him two days tops before he gets a ticket for it though.

[cv67]

running a real long length, like the others would seem a safe bet. You know he will put exh on real quick like. Its fun for about 10 minutes if he doesnt die of carbon monoxide poisoning. Dont get the alluyre of driving open headers or with cutouts, your car either sounds nasty or it doesnt but seems to be the trend today (esp with stock ones ugh lol)

[nickpohlaandp]

...Dont get the alluyre of driving open headers or with cutouts, your car either sounds nasty or it doesnt but seems to be the trend today (esp with stock ones ugh lol)

Agree 100%. I think it sounds like CRAP unless it's a high compression motor at the drag strip. On the street it's just annoying, especially if it's your car and you're stuck with listening to it.

[MadBill]

Just tune low load/low RPM by ear until a full system is in place. a.) Unless it's wash the cylinders/pig-rich,it can't do any harm. b.) as mentioned, it will likely be run for minutes, not hours with open exhaust.

[nickpohlaandp]

Just tune low load/low RPM by ear until a full system is in place. a.) Unless it's wash the cylinders/pig-rich,it can't do any harm. b.) as mentioned, it will likely be run for minutes, not hours with open exhaust.

Agreed. I can get idle where I'm comfortable by ear and (dare I say it) smell. I'm more concerned with cruise (2500-3000) and WOT being good. It's going to change anyway once he puts a full system on, so I'm not going to tear my hair out over it. I'll err on the side of rich until then. I'm not going to waste a ton of time tuning for an open exhaust on a street car.