Jump to content
LegacyGT.com

Air / Fuel Ratio's and you... Equiptment/Options/Opinions


cryo

Recommended Posts

Here are some helpful details related to AFR, Lambda, Wideband 02 sensors, Narrowband 02 sensors and such. Please provide opinions,experiences etc.

 

Air Fuel Ratio is a very commonly misunderstood concept and I didnt see anything like this posted so figured I would see if its helpful.

 

As simple as it sounds it is the amount of air to fuel ratio you are seeing inside/come out of the engine at any given point of time. This is measured from the factory 02 sensors all the time and the signal is then sent back to the ecu for processing. The 02 sensors are what are used to send the ecu signals to determine short term and long term fuel trims. The computer trys its best to stay at a preset AFR *air fuel ratio* to conserve gasoline during cruise and idle situations *light load*. This targeted afr is 14.7 for gasoline although with the 10% ethanol content in current gasolines the "total burn effect" occurs at a slightly richer mixture according to what some believe. This cruise and idle situation is called closed loop and is a process used to keep the vehicle constantly in the most effective range for emissions. The factory 02 sensors are called "wideband" sensors because of thier output capability but unfortunatly in terms of reading output at full throttle they are actually quite useless for a few reasons including the pressures created in the manifolds. They are designed to be very accurate within about 1.5AFR around idle and cruise situations *ie 13.5-16 afr*. Most Subaru 02 sensor readings from the computer peg at 11.XX since thats as rich as it will read regardless or true afr. It should be noted that the fuel mixture can actually be leaner than 11.XX and the factory sensor may still read 11.XX because of its lack of ability to produce true afr numbers that far away from stoich. *example: Factory sensor reads 11.14 when true wideband reading may read 11.3-11.6.*

 

It should also be noted that subaru targets richer idleing mixtures for different situations so its not uncommon to see swings from 14.2-14.7.

 

Well enough about closed loop fueling lets talk about open loop and wide open throttle afr. Openloop is a term used for when the computer stops making adjustments based on the stock 02 sensor readings and starts referering only to the primary openloop fueling table *+compensations*. Openloop basically occurs when your putting your foot in it in simple terms, the thing to note is there is a "delay" in the changeover between closed and open loop and can cause fueling issues for a modified car without changes in the tune to accomidate things like quicker spoolup and earlier peak boost/torque.

 

AFR is a term used as a ratio but changes depending on fuel being used. Because of this most tuners use a term called Lambda instead. Lambda is when all of the "fuel" in the cylinder has been burned and used as energy or for cooling causing a complete burn and nothing left in the cylinder. The biggest benifit with using lambda instead of afr is different fuels burn at different rates and will need different afr targets to acheive that perfect burn while lambda remains the same targets regardless of fuel. Although lambda is what I reference more I will base my details and explanations on AFR in this write up. Lambda is an easy conversion once you understand afr.

 

First off there is NO perfect afr or lambda to set and forget for any car, each car will want a little different afr but for the most part you dont have to reinvent the wheel. This is where doing a lot of research about your vehicle and what others have done come into play. Nothing will replace a dyno when truly calibrating afr or timing but knowing your "safe zone" can be extreamly helpful until your trying to wring out every last hp. AFR really doesnt change hp levels all that much when dialed in closley and comes down to safety more than anything else. The rule of thumb is to always start off rich because its a lot harder to hurt things quickly with an overly rich mixture although its very possible. Fuel is used to make power but at the same time is just as important in cooling the cylinder temps and keeping pre ignition and knock at bay. Thats the tricky part to finding an optimum AFR, rich best torque is key but many cars like a much richer mixture and would have a serious issue running that lean under all situations. Most subaru maps are set from the factory at a 12ish afr at the onset of boost tapering down to 10.3-10.5 which is safe but on the rich side during peak torque and high rpm on thier turbo motors. There are different theory's to making power with afr and as a personal opinion I feel power should never be made with lean mixtures but overly rich mixtures can be just as much of a power robber and must be leaned out to provide smooth power delivery. A overly rich mixture can feel sluggish and non responsive while a lean mixture can feel great but can easliy cause more damage. Contrary to the old saying "lean is mean" power actually starts to fall off on either side of rich best torque and lean best torque. Its a happy medium.

 

On to the Tools and Equiptment

 

Wideband 02 sensors used to be extremly expensive and were not an option for anyone other than high end shops and tuners. Now there are quite a few options that offer different formats to work with. The biggest thing to keep in mind is you have to be able to trust your equiptment so if you decide to buy used or cheap it may come back to bite you. Many times I have seen people try and save money on widebands and cost them motors or tons of time chasing thier tails tuning because of improperly working equiptment. Look at the features and benifits of each Wideband 02 kit and choose which ever suits your needs best. I chose the Zeitronix Datalogging software and am very happy with it. Most units work with romraider and Accesstuner Race now days. Something to note is the further away from the engine the Wideband 02 sensor is mounted the more of a "delay" you have to account for in your data. Some standalones will allow you to configure that but always something to keep in mind. If mounted behind a catylitic converter expect to see leaner values as well.

 

LC1 Wideband 02 sensor- One of the most common options for people right now, Bosch sensor, logworks software and cheap guage options as well.

 

Zeitronix wideband datalogger - Somewhat expensive but nice software,lots of options for display guages, Same bosch sensor

 

AEM wideband - works with guage but not actually sure if it has software availible. Never seen it advertised and only seen it used with AEMpro

 

PLX devices - works with guages, series of sensors or standalones. decent reviews as well. Make sure to purchase the usb adapter if you plan on logging to a laptop

 

These are a few of the name brand options but do research to see which will work best for what you are looking for. AFR should ALWAYS start at lambda *14.7 or 1.0* and steadily drop to your target afr in the primary openloop fueling table as long as the CL - OL settings have been tripped. Any bumps,divits or deviation from the target show changes might need to be applied to the scaling.

 

any questions,comments or opinions are more than welcome. Just figured I would try and post a little helpful information.

 

Dave

[sIGPIC][/sIGPIC]

Providing unmatched customer service and a Premium level of Dyno/E-tuning to the Community

 

cryotuneperformance@yahoo.com

facebook.com/cryotuneperformance.

Link to comment
Share on other sites

  • Replies 68
  • Created
  • Last Reply
PLX devices - works with guages, series of sensors or standalones. decent reviews as well. Make sure to purchase the usb adapter if you plan on logging to a laptop
If you are handy with a soldering iron, you can build a USB adapter yourself for about $45, which is roughly half of what PLX charges. I posted instructions at RomRaider:

 

http://www.romraider.com/forum/viewtopic.php?f=7&t=4299

 

I'm a big fan of PLX, mostly because of their graphical gauge. I have the gauge set for a seismograph-style display, so a glance will tell me what my AFR has been doing for the last 5 seconds rather than just what's doing right now. The scrolling display makes tip-in fueling issues easy to see in real time.

Link to comment
Share on other sites

Good write up. Just to go a lil off topic : what's the average output for AFR Circuit voltage? I'mchasing some crazy afr learning and correction issues. I'm wondering if my front o2 sensor needs replacing. It ranges from -1.2 to 1.8 Ma ( or whatever term is used). Any insight will be helpful.
Link to comment
Share on other sites

I use the LC-1 for my tuning. I have great results but you can buy aftermarket sensors that will plug into this unit. Be sure you buy an Bosch sensor or one from Innovative or you may not get consistant readings. Also, I made a calibration box to calibrate the unit and mounted it under the hood. I used a momentary push button switch, and two LED's (one for power on and one for calibration). It is compatible with RR but I prefer to use the standalone Innovative software.
Link to comment
Share on other sites

I use the Zeitronix ZT3 right now and like the software options *displaying graphed AFR and Lambda on 2 different lines*.

 

I use to use the ZT2 untill it went out on me, I really liked the features of it as well as the options of what could be datalogged *rpm,tps,boost,egt plus 2 inputs aux inputs etc*

 

I like to resize my wideband window and locate it in the lower right corner of the romraider logger or ATR, graphing the data is VERY usefull like NSFW mentioned.

 

I own a LC1 as well and think it does a great job for the money.

 

Both units use a bosch 17014 LSU 4.2 sensor.

 

Dave

[sIGPIC][/sIGPIC]

Providing unmatched customer service and a Premium level of Dyno/E-tuning to the Community

 

cryotuneperformance@yahoo.com

facebook.com/cryotuneperformance.

Link to comment
Share on other sites

Shell- i normally watch the stock 02 sensor and compare it to a wideband to see if they are pretty close or way off as well as look at a few other things. Pm me with your situation and i can see if i can give you any insight as to your af learning issues.

 

Dave

[sIGPIC][/sIGPIC]

Providing unmatched customer service and a Premium level of Dyno/E-tuning to the Community

 

cryotuneperformance@yahoo.com

facebook.com/cryotuneperformance.

Link to comment
Share on other sites

  • 2 weeks later...

Just purchased a Innovate wideband clamp used for $45 for when I rent the dyno. Still cannot believe they charge $79 new but the clamp is more sturdy than I expected.

 

Dave

 

http://forums.pelicanparts.com/uploads20/clamp1338738902.jpg

[sIGPIC][/sIGPIC]

Providing unmatched customer service and a Premium level of Dyno/E-tuning to the Community

 

cryotuneperformance@yahoo.com

facebook.com/cryotuneperformance.

Link to comment
Share on other sites

just make sure the o2 sensor is point down in that. a local tuner here used that clamp for a while and was pissing through o2 sensors since our tailpipes and bumper dont leave room to mount the sensor upright, the thumbscrew hits the bumper, so we'd have no choice but to mount it upside down and clog up the sensors with soot.
Link to comment
Share on other sites

just make sure the o2 sensor is point down in that. a local tuner here used that clamp for a while and was pissing through o2 sensors since our tailpipes and bumper dont leave room to mount the sensor upright, the thumbscrew hits the bumper, so we'd have no choice but to mount it upside down and clog up the sensors with soot.

 

Based on the design i kind of agree but i cant say its an optimal setup rightside up or upside down. All flow going to the sensor will be forced into it instead of being plumbed into the exhaust where flow goes past it.

 

Either way it seems to work ok so far and i have 4 different bosch sensors and two different wideband options on hand just incase one fails mid tune or gives me readings i question.

 

Dave

[sIGPIC][/sIGPIC]

Providing unmatched customer service and a Premium level of Dyno/E-tuning to the Community

 

cryotuneperformance@yahoo.com

facebook.com/cryotuneperformance.

Link to comment
Share on other sites

it's not the flow, it's gravity and where the carbon settles. upside down o2 sensors don't last long, period. that's why certain wideband manufacturers suggest mounting the sensor at no less than a 15* angle in the pipes.

 

Actually some manufactures recommend a specific mounting position and to make sure the sensor does not face up as it can damage the ceramic heating element from moisture since its more likely to hit it. Like I said, I'm not a huge fan of the design since it forces all flow through the sensor *carbon,moisture,etc* and my look for something else down the line. I know of a few different dyno shops using them currently without issue so who knows.

 

I'll report back with my personal findings in a few months.

 

Dave

[sIGPIC][/sIGPIC]

Providing unmatched customer service and a Premium level of Dyno/E-tuning to the Community

 

cryotuneperformance@yahoo.com

facebook.com/cryotuneperformance.

Link to comment
Share on other sites

  • 2 months later...

So far i have determined the wideband holder works well, its not ideal and the condensation will cause issues and eventually burn out sensors regardless but its a good piece.

 

I think i may eventually build my own with a little different design down the road just for testing purposes.

 

Dave

[sIGPIC][/sIGPIC]

Providing unmatched customer service and a Premium level of Dyno/E-tuning to the Community

 

cryotuneperformance@yahoo.com

facebook.com/cryotuneperformance.

Link to comment
Share on other sites

  • 1 month later...

I don't think o2 sensor mounting really matters for a temporary install such as tuning a car on the dyno.

 

You don't want a sensor installed facing up for a permanent install.

 

Water is a byproduct of combustion. When the water leaves the combustion chamber it is in vapor form. Problems with o2 sensors occur when you shut your car off and the exhaust cools. The water vapor condenses and collects in liquid form on the bottom of the pipe.

 

Ever seen a car with water dripping from its tailpipe? That's a sign it hasn't been running very long and the exhaust pressure is pushing the water out the tailpipe. Once the pipes heat up all the water vaporizes.

Link to comment
Share on other sites

Just a little input 14.7 PSI is the pressure pushing against Earth all the time. Yes if it wasn't for that pressure we would all explode from nothing holding the body together. Which 14.7 is considered a perfect combustion of what ever carbon you might be burning. If it wasn't for us wanting to run dinosaur liquids through engines your oil wouldn't turn black. Your exhaust wouldnt have carbon build up. Just some knowledge. Soo how you you tune for other fuels. Propane, Coal, Diesel, E85 is being used and is understood how to tune.

 

14.7 is a stoichmetric ratio that has NOTHING to do atmospheric pressure. It just happens that 14.7 is the appropriate ratio for gasoline. For E85 is 9.76, so it has everything to the fuel you're burning. Atmospheric pressure doesn't magically drop if you run your car on E85.

Link to comment
Share on other sites

^^ on top of that, 14.7:1 is just the stoichiometric AFR, and gives the most efficient burn in the combustion chamber and results in the lowest emission of hydrocarbons and NOx gases. I believe the most powerful ratio is on the rich side, closer to 13.xx:1, but theres multiple variables to account for.
Link to comment
Share on other sites

Just a little input 14.7 PSI is the pressure pushing against Earth all the time. Yes if it wasn't for that pressure we would all explode from nothing holding the body together. Which 14.7 is considered a perfect combustion of what ever carbon you might be burning. If it wasn't for us wanting to run dinosaur liquids through engines your oil wouldn't turn black. Your exhaust wouldnt have carbon build up. Just some knowledge. Soo how you you tune for other fuels. Propane, Coal, Diesel, E85 is being used and is understood how to tune.

And to be pedantic, our bodies would not explode at zero atmospheric pressure. Our bodies are very good at maintaining equal pressure inside as out so the difference in pressure is always near zero.

 

Now breathing would be another matter as zero pressure would mean no air...

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.




×
×
  • Create New...

Important Information

Terms of Use