Checking Afrs Using Wideband In Tailpipe

[Wacky Dee]

reading another topic recently made me think about this as I'd never considered it before .. most tuners seem to stick a wideband sensor into the tail pipe when tuning the AFRs.

How accurate is this method compared to having a wideband stuck inside the dump pipe directly eg. throguh the o2 sensor hole. Does the cat affect AFRs readings or would you get the same readings from tail pipe as you would from the dump pipe ? Cheers

[toddlls]

Not really, ideally each exhaust port should have a sensor tapped into it for an accurate description of exactly how the motor is performing, what it does give is a generalised reading across the board to get the mixtures within an acceptable range & considering every tuner I've ever used has done this method & i have neva had a motor go bang due to incorrect fuelling levels when winding up the wick so-to-spk it seems to work ok.

ps. Better if an actual tuner responds so you can get more accurate info-but this is what i have read when investigating fuel mapping & turbo charged applications & they all recommend sensors at each port for big hp numbers & huge dollar spends

[Duncan]

The 02 sensor is designed to work a certain distance from the ehaust ports, normally about 50-80cm. Best to have it arund the cat somewhere but that just isn't reasonable for a shop to weld bungs on your exahust just to tune ti

[The Dan]

Not really, ideally each exhaust port should have a sensor tapped into it for an accurate description of exactly how the motor is performing, what it does give is a generalised reading across the board to get the mixtures within an acceptable range & considering every tuner I've ever used has done this method & i have neva had a motor go bang due to incorrect fuelling levels when winding up the wick so-to-spk it seems to work ok.

ps. Better if an actual tuner responds so you can get more accurate info-but this is what i have read when investigating fuel mapping & turbo charged applications & they all recommend sensors at each port for big hp numbers & huge dollar spends

An even better method is to use thermo sensors for each manifold runner. You can more accurately tune this way as AFR sensors can be a bit laggy or problematic with readings when high flow and temperature is involved

[zebra]

I thought it was EGT probs near the ports, not o2 sensors

Edit: beaten to it

[JCaSs1001]

can EGT sensors be used not near the ports, or wont it be effective??

[Swiper the Fox]

egt is how the big drag cars are tuned...thats how Mark is tuning the Wedlock Camry. The initial tune on the dyno using wideband in the dump pipe then perfected on the track using egt's that are logged and are checked after each run.

My car is tuned using a dump pipe mounted Bosch sensor with a tailpipe mounted one to cross reference the readings.

Dunc's ive mounted my sensor about 200mm from the turbine outlet...not good for longevity but the best for accuracy when tuning this way. Techedge recommend mounting the sensor much further down the dump so it is not affected by the heat as much, this is only recommended to make the sensor last longer.

Edited July 24, 2009 by DiRTgarage

[Duncan]

My car is tuned using a dump pipe mounted Bosch sensor with a tailpipe mounted one to cross reference the readings.

yep same, to me this is the safest way to do it.

Dunc's ive mounted my sensor about 200mm from the turbine outlet...not good for longevity but the best for accuracy when tuning this way. Techedge recommend mounting the sensor much further down the dump so it is not affected by the heat as much, this is only recommended to make the sensor last longer.

yeah I think we are using the same kit then. I've just replaced my sensor after 5 years which I reckon was a pretty good life

I'm sure EGT is the best way to do it but you need 6 bungs in the exhaust ports, 6 sensors, 6 controllers. All too hard for your average street car, but probably worth it when you need that last 2% by tuning fuel in individual cylinders

[_Ryan_]

always wondered if a cat would effect the AFR's that a sensor at the exhaust tip reads...

Dirt what cat do you run?

[Swiper the Fox]

always wondered if a cat would effect the AFR's that a sensor at the exhaust tip reads...

Dirt what cat do you run?

good point Ryan...but i cant comment. The cat in my car is long gone...i do have a magic cat from Magic Performance in Sydney to run on the street, but these days i rarely drive the car on the street.

[The Dan]

always wondered if a cat would effect the AFR's that a sensor at the exhaust tip reads...

No, it does not effect the readings. As long as the cat is not blocked, but then again, if it were blocked, you'd have trouble starting the engine

[The Dan]

yep same, to me this is the safest way to do it.

yeah I think we are using the same kit then. I've just replaced my sensor after 5 years which I reckon was a pretty good life

I'm sure EGT is the best way to do it but you need 6 bungs in the exhaust ports, 6 sensors, 6 controllers. All too hard for your average street car, but probably worth it when you need that last 2% by tuning fuel in individual cylinders

It's probably not so much to get that extra 2% but to ensure that the engine lasts longer than 2% of the time. When you have high temps in one cylinder, you can find out why before you melt a piston. An 02 sensor in the tailpipe will only tell you a combination of all cylinders.

Most factory tunes are done by individual EGT's when the engines are run in. It is the most accurate way to tune an engine.

Even if you only have it attached when you are tuning, it's going to save a lot of time, money and headaches.

I'm pretty sure they only cost about $800-$1000 to set up completely so it's not that much when you consider how many dollars go into some engines.

[Swiper the Fox]

It's probably not so much to get that extra 2% but to ensure that the engine lasts longer than 2% of the time. When you have high temps in one cylinder, you can find out why before you melt a piston. An 02 sensor in the tailpipe will only tell you a combination of all cylinders.

Most factory tunes are done by individual EGT's when the engines are run in. It is the most accurate way to tune an engine.

Even if you only have it attached when you are tuning, it's going to save a lot of time, money and headaches.

I'm pretty sure they only cost about $800-$1000 to set up completely so it's not that much when you consider how many dollars go into some engines.

engine lasting 2% of the time...unfortunately Duncan knows exactly what you mean.(not a dig)

yes EGT's showed up a faulty injector very quickly in the Wedlock car when the AFR's only appeared slightly rich. Using methanol this could have quickly hydraulic'd(sp*) a cylinder and ended in an expensive mess

Edited July 24, 2009 by DiRTgarage

[Sydneykid]

reading another topic recently made me think about this as I'd never considered it before .. most tuners seem to stick a wideband sensor into the tail pipe when tuning the AFRs.

How accurate is this method compared to having a wideband stuck inside the dump pipe directly eg. throguh the o2 sensor hole. Does the cat affect AFRs readings or would you get the same readings from tail pipe as you would from the dump pipe ? Cheers

It slows down the response, obviously takes time for the exhaust to travel from the engine to the tail pipe. No big deal there at full throttle, but it can be a problem at low exhaust gas speeds. Plus you need to be careful with large diameter tailpipes that outside air doesn't sneak in and dilute the readings.

Cheers

Gary

[DCIEVE]

I'm sure EGT is the best way to do it but you need 6 bungs in the exhaust ports, 6 sensors, 6 controllers. All too hard for your average street car, but probably worth it when you need that last 2% by tuning fuel in individual cylinders

There are plenty of kits available come with everything you need, you can have one all installed and running for ~1000-1500 (roughly the cost of a good wide band o2 sensor). I'm baffled why more people don't do it.

I'm not sure that its for that last 2%, my only reasoning was to ensure everything is safe - even with a standard plenum I have very large corrections so you can be reasonably sure most people have a few cylinders running up to 10% leaner than the average number the o2 sensor is telling you - and the lean cylinders aren't the ones everyone around here blindly claim.

[Duncan]

well...wide band 02 set is $256 over here http://wbo2.com/2j/default.htm, and I still think 1500 is understating the cost of 6 sensors, controllers, display, manifold installation etc.

but,....no doubt if you have spend over $10k on a motor, 1500 is only a little more for safety.

in practice....almost everyone tunes a car with a wide safety margin in o2 ratios to deal with the risk....how many dyno graphs on here are 11.2-11.7 at full load. Like I said unless you are after the last %% in performance you will just accept this margin...I certainly do and have never had a motor die with a tuning problem , and the old girl still makes enough power to keep up with the 6l commodores

[unique1]

i run 6 egts and 2 dataloggers setup to log them and it cost around $1000 when the US dollar was really good so around the $1200 mark now i would say. They are a damn good investment and as dcieve says its showing alot of different readings to the so called hottest cylinders being claimed on here, i think people underestimate the difference is cylinder temps across the board. A rebuild from melted pistons cost me $4000 im sure $1200 isnt much to ask when your pushing a motor pretty hard.

[DCIEVE]

Check out the innovative stuff... the complete egt set-up set me back roughly 1k a year or so back and a mate welded bungs into the manifold. The benefit is you can run the innovative o2 in series with the egt and datalog the whole lot. The only downside is I can't get it to speak to the ecu so egt & o2 are logged seperately to everything else in the ecu.

I was prompted to go with egt's after watching friends destroy expensive motors with detonation running 'safe' afr's and conservative tunes (stuff all timing).

[STATUS]

always wondered if a cat would effect the AFR's that a sensor at the exhaust tip reads...

Dirt what cat do you run?

yes it does, BUT most cars get tuned via the tailpipe as it is perfectly accurate for power pulls etc as the velocity of the gasses many inaccuracies. Idle cannot be checked properly at the tailpipe without a myriad of tricks and experience.

Any big power setup gets a specially placed bung for tuning @ my shop, and careful egt monitoring if the customer has the budget.

To be honest experience is more important than placement on 95% of tuned cars.

Edited July 24, 2009 by URAS

[The Dan]

yes it does, BUT most cars get tuned via the tailpipe as it is perfectly accurate for power pulls etc as the velocity of the gasses many inaccuracies. Idle cannot be checked properly at the tailpipe without a myriad of tricks and experience.

Any big power setup gets a specially placed bung for tuning @ my shop, and careful egt monitoring if the customer has the budget.

To be honest experience is more important than placement on 95% of tuned cars.

If you took measurements from a car from the tailpipe, then from the bung before the catalyst, do you actually notice any difference in AFR? I didn't think any o2 sensor is that sensitive that it could measure the difference?

The catalyst removes oxygen from the oxides of nitrogen and then combines the oxygen with the carbon monoxide to create carbon dioxide. So it really only takes the oxygen from one place and puts it in another and both before and after the cat, the wideband doesn't recognise the gases before they are split with their other particle.

Or are you referring to it effecting the result in that it is slower, not so much changing the reading?