Fitting dual wideband 02 sensors
Turbo Mini Forums

As far as measuring pressure pulses in the turbo manifold are concerned, this is very difficult due to heat. The sensor will need to be very close, if not directly connected to the manifold otherwise the pulses will be lost due to the damping by the connection pipe. As far as I am aware, no such sensor is available. On the 1293 we had to put in quite a length of pipe to get the temperature down enough to stop it melting a rubber hose.

Also, the sample rate of the o2 sensor will be nowhere near high enough.

Whilst this sounds like a very interesting electronics project, I can only see it getting us back to where we were with sample tubes 5 years ago.

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."

What would be useful information is the offset caused by heat and pressure on a particular type of installation.

The easiest way, as I see it (practical without electrickery), would be to put 2 O2 sensors at the same point of the manifold, upstream of the turbo. One connected by sample tubes and the other directly connected. Simples.

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."

In that scenario, it wouldn't be a fixed offset though as the sample tube one "should" read the actual AFR as it would be unaffected by pressure/temperature variations whereas the directly installed would have a variable offset with varying pressure, and a varying offset with temperatures above 750C (if it proved impossible to limit it to 750C).

Anyway, you know I like electrickery

I found the data on temperature, don't know how I missed it before as it's on the same page as pressure....

6-7% on cell current per 100K (which is per 100C as we are talking relative to 750C).

@Phil, it's also worth mentioning that if you can't maintain a 750C maximum, you won't be able to be able to datalog or do any real time calculations involving temperature with an SLC Free. So far as I can see from it's schematic there is no I2C bus (which is what the SLC OEM uses) to export that data, it is limited to displaying it locally only.

EDIT - just looked again at the schematic and the physical PCB I have and, although the user connectors have no access to I2C, there is an unused "prog header" which is marked SCL and SDA so there is a slim possibility - if the firmware is similar enough to the SLC OEM - that the digital data may be available.
I'll try asking on his Forum.

Edited by Rod S on 13th Oct, 2014.

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

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

Although I used the singular "offset" in my head I was thinking "offset map"

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."

The Arduino CAN board I'm looking at is £8 so I might as well trial it. I would use a Proto Shield (veroboard) for basic components , stacked onto the CAN shield, stacked onto the Arduino. I like the idea of the Arduino shields/boards all having the same form factor and header pin-outs, so should stack nice and neatly inside the ECU case and minimal soldering / wiring to do.

I'm not too bothered about the 0-5V outputs. Digital would be nice, but considering most other sensors are analogue (with a few exception such as hall sensors), I think as long as you're aware that you should calibrate them first (just as you would for a TPS), it's no longer an issue. In Scott Clark's presentation he mentions the problem, and it's something I noticed early on when comparing the AFR dial on my laptop screen to the my AEM dial. If I get the SLC Free, I may try to make the screens removable (if they aren't already?) and consider rearranging capacitors if they're a problem, so that I can get them in the ECU case.

With regard to pressure pulses, even if the LSU hardware is fast enough to be affected by an individual pulse (maybe on an single runner of a slow idling V8), I'd expect the sesor / controller to filter this out. I found that the AFR reported by the AEM unit pretty fast, but couldn't see any AFR jitter in phase with the engine revs (and I did try idling as low as 600 RPM at one point). My gut feeling is that an LSU and controller handle, or are immune to errors due to individual pulses, or we'd know about it from tuning NA engines. The problem then, is that if I combine a clean AFR signal and the raw, jittery pressure signal, I end passing a jittery AFR signal to an unsuspecting MS. I know that MS2 and MS3 each have settings that let you schedule where in the engine cycle you take a MAP reading (because of induction pulses), but there's no reason to expect MS to handle an AFR sample in the same way, because it wouldn't normally expect AN AFR to vary depending crank degrees.

I'm not trying to solve a problem that I don't yet know exists yet, but just pointing out that the results could be very strange, and Arduino is an extra tool to tackle problems if needed. When you start to ask those questions like "do I pick the peak or the average or some sort of time weighted average", you start to think that you may need something more than discrete components or a simple formula in MS.

I like Robert's idea about the boss. I think it has more in common with sample chambers and may be a way to simplify the sample chamber construction but only if the washer hole was much more restrictive than the brake pipe. I assume the pipe would join back onto the exhaust otherwise the MOT would have a fit. I think I will drill a 1mm hole directly in the exhaust then fix a long boss directly over it. I think pressure pulses should be able to pump fresh exhaust in and out the hole easily . If the sensor response was too sluggish, I imagine think I could open up the hole a small amount without introducing much more heat.
As for the boss itself, I will use stainless as it's slightly worse at conducting heat, notch the end and position 1mm off the exhaust surface. I can TIG a small radius all the way around, instead of just filling the gaps as you would do with MIG. My theory is that less surface area at the weld joint will mean a smaller path for the heat to soak in. Alternatively, I could drill the hole then weld the boss to an exhaust U-clamp and tighten it over some kind of insulating gasket. I will make a simple heat shield / heat sink, but for simplicity, I'll would test whether I can get away without.

LSU 4.9 sensors for £38 --> http://www.ebay.co.uk/itm/141419753894
At the moment, there's only one seller at that price (and the cheapest LSU 4.2 is a higher price), but it makes me a bit less worried about melting a sensor.

Pictures of the SLC Free here when I played with it
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=561905

Looking at later pictures by others, he has supplied longer spacers. Better answer would have been tantalum caps but he went for cheap.

The LCD display just plugs in, just replace the header with a 16 way ribbon cable if you want them remote.

Alan only increases the kit price by US$50 to include the LSU so that's pretty comparable to your eBay one depending on whether you get stung for import duty from 14point7 - he used to ship from homeland Canada but now routes via US postage so higher risk....


EDIT - also need to find a genuine Bosch datasheet for the 4.9
In the eBay listing it says exhaust gas pressure <4bar
Don't know where he got that from but, if true, it's a lot more than the 4.2 graph goes to.
Hmmmmmm....

EDIT 2 _well I found the datasheet (possibly not the full one but a good starting point)
http://www.bosch-motorsport.de/media/catal...79147659pdf.pdf
and it is way more tolerant to pressure and temperature than the 4.2

Definitely worth a rethink...


EDIT 3 - but anyone else reading this, the 4.9s are only compatible with certain controllers, you can't just swap a 4.2 with a 4.9 unless the controller is switchable (like my old TechEdges) or has the option of different components like the SLC Free. My SLC OEMs will only work with a 4.2

Edited by Rod S on 13th Oct, 2014.

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

Edited by PhilR on 13th Oct, 2014.

See my edits above re. the 4.9

Re the pulses on a long tube, I have to disagree with your thoughts.
EDIT - no, hadn't read it properly.... (end edit)
A long narrow tube is perfect for damping out pulses with a compressible fluid (exhaust gas).
A closed end system will only record the pulses with an IN-compressible fluid.
EDIT - so if you want to see/measure pulses, a short large tube, if you want to damp them out physically, a long small tube... (end edit)

Otherwise I agree with what you say.

Edited by Rod S on 13th Oct, 2014.

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

A better datasheet that confirms the absolute maximums of the 4.9 and where it's accuracy starts to drift - way higher temperature and pressure than the 4.2
http://industrial.boschautoparts.com/Techn...ambdaSensor.pdf

Enjoy.

EDIT - obviously designed for lean combustion engines, hence the higher temperature limits, the higher pressure is probably just a side effect.

Edited by Rod S on 13th Oct, 2014.

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

Edited by PhilR on 13th Oct, 2014.

phil,i dont think an mot tester would really react to two bit of brake pipe hidden away somewhere , also you could work out a ratio between the brake pipe area and the inlet hole area ,and just up the inlet hole dia towards parity .

....although, with rod finding the things may take 4 bar 60 psi ,you could almost make the inlet hole any size !

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

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."

Exactly like that. Is that one long enough to stop it melting the hose?

It never got ran in anger before the project was shelved. Going back in a car soon though

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."

That looks a little bigger than "brake line"...
Do you guys think Kunifer brake lines will allow a sufficient supply of air?

Yes, that's 6mm stainless. I don't believe that brake pipe should go anywhere a hot turbo manifold.

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."

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

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.

You'd have to ensure that no actually flows through the pipe (as it would with a sample chamber) as that's a completely different model. Stainless work well in this model as it (and the gas inside) has poor heat conductivity.

The only question is whether the heat transfer would be aided by the pressure waves in the exhaust gas even though there's no flow overall. A reasonable precaution would be to partially seal the end nearest the exhaust to damp down the pressure pulses - either weld up the end then drill a small hole through the weld, or crimp it to cause a restriction.

Edited by PhilR on 13th Oct, 2014.

Duplicate post

Edited by PhilR on 13th Oct, 2014.

Is the 70mm a typo (ie, it should say 700mm) or is the thermocouple pushed all the way down the tube to be within 70mm of the flame ?

If so I think it's because you are heating externally.

The exhaust gasses will pulse and heat far better from the inside.

The ultimate test will be an LSU read by the 14point7 stuff or a K type thermocouple in a dead leg on a real manifold under boost.

Not being negative but what you have shown seems too good to be true.

Tomorrow I'll try to get a photo of one of my K type where the outer fibreglass sheath was destroyed just by it accidentally touching one of the wideband sample chamber sample tubes.

Edited by Rod S on 13th Oct, 2014.

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

in the past i have measured ex pressure before the 1st turbo ,and between turbo's on a compound twin stage turbo sytem .

i just used a brake pipe connection welded to the exhaust tube ,then about 20 inches of kunifer brake pipe ,then a flexible black rubberish tube to inside the car and a pressure guage.

never had a problem.

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

No not a typo - 7cm.

In the photo, the probe ie 3cm inside the right hand end, with a small piece of paper wedged in the end, after a lot of heating I realized it wasn't going to go 1 degree over ambient, so I kept moving it in unit I got a decent reading. At 90 degrees actual I kept heating for several more minutes to make sure it had stabilised, then pulled the thermocouple to see how fat it was in. The wire is rigid so it went all the way in and can't coil inside, and I touched the pipe about 10cm from the flame and that was hot but easily bearable - maybe 50 /60 degrees actual

Rod, With a sample chamber you're sending the hot gas right through the tube. For a sample chamber, the stainless would work against you as it's a poor conductor of heat it won't radiate the heat effectively, and the exhaust gas gets from one end to the other at almost the same temperature.

When using the pipe to transmit pressure changes, not gas movement, the pipe is (almost) blocked at both ends. The only way for heat to get through is conduction. Stainless is a now an ideal material now, as the only way heat can get through is to conduct through the air (very bad conductor), or conduct through the stainless (also a pretty bad conductor).

I know it's counter intuitive based on what you've already seen yourself. It only took a few minutes to set this up, so if anyone can suggest improvements to this experiment, I'm going to try it again tomorrow and get some more figures.

Edited by PhilR on 13th Oct, 2014.