Fitting dual wideband 02 sensors
Turbo Mini Forums

Understood I have flow but I would be very surprised at 70mm for so little heat in a dead leg.

Conduction in stainless isn't much different to steel - at the end of the day stainless is only Fe with a few different alloying elements to mild steel.

But, as I've always said, people can predict what they want but only a few of us actually try to measure things.

So, yes, please keep the testing going.

Schrödinger's cat - so which one am I ???

Good info. I think I'll be ordering a pair of LSU4.9's...... Sorry I can't input on this topic as I've got a full compliment of ports, but I already have a wideband pre and post turbo with a Delta P (DPF) sensor. It'll be a bit yet before I have any data for comparison though.

Just in case you didn't know, you have to have a controller that explicitly supports the 4.9. It's not a simple plug in replacement for the 4.2. That requires different hardware and different code in the controller.

http://www.jbperf.com/

Cough...............

http://www.jbperf.com/

When welding stainless, I've always read that you need slightly less current as it doesn't wick the heat away, and when you weld Aluminium you can struggle to get enough heat into it because it conducts away so easily. To put some numbers on it, see bellow, but I can't remember what on earth the units mean.

http://www.engineeringtoolbox.com/thermal-...vity-d_429.html

Thermal Conductivity at 25 degrees C - k - W/(m.K)

Copper 401
Aluminum 205
Iron 80
Steel, Carbon 1% 43
Stainless Steel 16


I'm grateful for all the input so far, even you're comment about the DPF sensor Sprocket (I've never heard of one before, but just looked it up and realise I need one for another project)

I'm also glad of any "that can't be true" comments. I am pretty much making this up as I go along, so challenge me and I'll try and justify it.

Edited by PhilR on 18th Oct, 2014.

http://industrial.boschautoparts.com/Techn..._0281002772.pdf

Edit, the daasheet above is a 100kpa sensor so not much use, sorry but you get the gist.

Edited by Sprocket on 13th Oct, 2014.

I think you'd be much better off with 2 absolute pressure sensors. Having a differential pressure gives you no indication if the post turbo sensor is seeing any significant pressure or not.

Or it might be that I'm not seeing what you're actually using it for.

http://www.jbperf.com/

I was interested in something like that for a completely unrelated project - to continually check the balance of a pair of carbs. I don't actually think that one would work now that I've seen the specs, but good to know.

Edited by PhilR on 13th Oct, 2014.

Schrödinger's cat - so which one am I ???

I've just gone back to my old TechEdge units and it is both change jumpers and load alternative firmware with them - easy because they provide the firmware on their website and from what I remember when I first built them and they recommended an immediate upgrade it was just as easy as, say, updating the firmware on an MS2/3.

And thinking a bit deeper it is probably more than just the resistor on the SLC Free. Although the PCB is the same and the instructions say install or omit the resistor depending on which LSU, the kits are sold specifically for one or the other so I guess, although the microcontroller is physically the same, they most likely have different code pre-loaded. EDIT, not that there is any label or marking on the one I have to say it is coded for 4.2 only but I still suspect it is the case.

Edited by Rod S on 14th Oct, 2014.

Schrödinger's cat - so which one am I ???

I've just ordered two of the SCL Free with 4.9 sensors. I had a quick look on their forum and there was one post that seemed to suggest the firmware was different between 4.2 to 4.9. I couldn't really find out much other info on them, but for the price, I'll be happy if they just work.

Would be interesting to see if there have been any other changes. I saw pictures of another unit that had longer board spacers to clear the caps that were a problem on yours. It looked like screen pins were then raised up and not seated fully in their socket. I'll get a better idea when they turn up.

Edited by PhilR on 14th Oct, 2014.

On 13th Oct, 2014 PhilR said:
Quick experiment with stainless tubing...



This is 10mm stainless tubing that I've heated to 800-900 degrees C , 30mm from the left hand end, using Mapp gas. The camera goes mad for infra-red light so it's not actually white hot, but it's bright red.


In a minute, the temperatures seemed stable and at 5 minutes of heating the temperatures were a steady 70 degrees over ambient at 70mm from the centre of the flame.

The maximum working temperature of silicone tube is perhaps 250 C, so assuming an under bonnet temperature of 100 C and temperature change from conduction at 70 C , I think you could plumb a sensor in with a 70mm pipe welded directly to the exhaust.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

On 14th Oct, 2014 Paul S said:

I agree:

Schrödinger's cat - so which one am I ???

On 14th Oct, 2014 Rod S said:

You complain about me using electrickery and here you are, running a simulation rather than getting a blowtorch out
It does confirm lack of gas flow means sod all heat transfer along the tube, surprising to me at least.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

On sample chambers, do you use any other restriction? What if you used a shorter length of 6 or 10mm tube to keep the strength, and had a restrictor at the end of the tube.

I've been thinking about how to make the o2 boss for the non sample tube version. I've seen some EGT logs that Paul posted in 2008, that showed temperatures around 700 C. Would you say these are typical temperatures? Do you remember how far into the exhaust flow the probes were positioned?

Edited by PhilR on 14th Oct, 2014.

Edited by Paul S on 14th Oct, 2014.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

To confirm, there is definitely a difference in the code in the SLC Free between the 4.2 and 4.9 versions. At a minimum, there are some different PID settings and a different temperature target.

http://www.jbperf.com/

Schrödinger's cat - so which one am I ???

A simple sticker on the board that says "4.2 only" or "4.9 only" and a short notice about it somewhere would go a long way towards making it obvious that you have this limitation.

http://www.jbperf.com/

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

For SCL Free, there are different firmwares for 4.9 (B) and 4.2 ©. In the SLC Free manual it states "SLC Free B displays a sensor temperature range of 740C to 820C, SLC Free C displays a sensor temperature range of 670C to 828C"

That means when the sensor is cold or disconnected, SLC Free B firmware will show 740C and SLC Free C firmware will show 680C. That is the way to tell which firmware you have in case you forgot what you ordered.

With regards to the 4.2 vs the 4.9, in terms of operating temp and max temp the 4.9 seems to be rated for ~25-50C higher. It is not a huge advantage but it is an advantage nonetheless. In terms of pressure dependency they look identical to me, it is hard to say for sure as the 4.9 datasheet has more information about pressure dependency where as the 4.2 datasheet just makes a 1 sentence reference to it. In terms of temperature dependence the 4.9 has roughly half the temperature dependency as the 4.2, so the 4.9 has an advantage there.

A lambda sensor in any installation is subject to heat and exhaust pressure. It would be good if ontop of lambda you had sensor temperature and exhaust back pressure.

The lowest hanging fruit on the tree is showing sensor temperature, it does not require any additional sensors and during the normal course of controlling a lambda sensor the controller will need to know sensor temperature in order to properly control it. Most of my lambda controllers display temperature, next to AFR/Lambda sensor temperature is the most important metric, exhaust pressure is generally less important than sensor temperature atleast for the Bosch sensors.

Bosch sensors are more prone to temperature effects than NTK sensors, NTK sensors are more prone to exhaust pressure effects than Bosch sensors. If I had the choice between a bosch sensor and a NTK sensor for a typical performance installation, I would pick the Bosch over the NTK because temperature can be controlled (as long as you know the sensor temperature) by where you place the sensor. Exhaust pressure can not be controlled generally.

There is one brand of lambda controllers that suggests you should put a heatsink on the lambda sensor, however that brand never shows sensor temperature so it is like a doctor telling you to get chemo without showing any data to support that you have cancer. That brand of lambda controllers does not properly detect sensor temperature in the first place, so I would take whatever they suggest with a big grain of salt.

For my controllers, if you see the temperature constantly above 750C for the 4.2 and 780C for the 4.9, then you should either put a heatsink on the sensor or move the sensor farther away from the engine outlet, there is no room for imagination or interpretation when you know the sensor temperature. Also if you notice that the sensor is constantly below 750C for the 4.2 and below 780C for the 4.9, then you need to move the sensor closer to the engine outlet, there are other things that can cause a lambda sensor to be too cool such as low battery voltage or poor wiring or if you run a race car with small or no alternator.

I always wanted to put in exhaust pressure compensation in my products, but my strength is in electronics and developing a back pressure monitoring kit is too far outside my area of expertise. If anyone here wants to put together a kit for exhaust pressure monitoring, I will happily buy kits off you for resale or direct my customers to you.

something else that occured to me is does the combination of temp and pressure have an effect ?

eg , if the sensor hits 700c and 30 psi back pressure ,would it be as accurate as 700c and 20 psi , or 800c and 10 psi .?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Good to see some input from an expert in the field.

Those of you contemplating putting a wideband sensor on the centre branch of a Metro Turbo manifold should be aware that even at moderate boost, say 0.8 barg, the average cycle EGT at the head flange is around 1000 Deg C. Also the average pressure will be around 3.0 barg, peaking at around 5.0 barg.

On an LCB style manifold, it will come down to around 2.7 barg and 850 Deg C at about 0.5m from the head.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."