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The mkiv Supra Owners Club

Trouble with understanding Air to Fuel Ratios


Carl_S

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Okay,

 

A ratio is the amount of different items in a mix. In this case Air and Fuel. 14.7 parts of air and 1 part of fuel is the theorical ideal (I believe), however it isn't the safest and that ratio only applies to petrol. Methanol and other fuels have a different ideal ratio also known as stoic.

 

Running lean will result in very high tempreatures and detonation, running rich will rob power and eventually borewash. Neither is ideal,but rich is better.

 

AFR gauges are a must have on any modded car IMHO. They aren't very difficult to fit, hole drilled in the exhaust near the engine, and a unit is welded on so the AFR sensor can be screwed in.

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Okay,

 

A ratio is the amount of different items in a mix. In this case Air and Fuel. 14.7 parts of air and 1 part of fuel is the theorical ideal (I believe), however it isn't the safest and that ratio only applies to petrol. Methanol and other fuels have a different ideal ratio also known as stoic.

 

Running lean will result in very high tempreatures and detonation, running rich will rob power and eventually borewash. Neither is ideal,but rich is better.

 

AFR gauges are a must have on any modded car IMHO. They aren't very difficult to fit, hole drilled in the exhaust near the engine, and a unit is welded on so the AFR sensor can be screwed in.

 

 

Very useful. So an AFR gauge would not use an existing O2 sensor? In an AFR fitting kit, what's in the fitting kit part? How involved is it for a newb to fit?

 

 

 

 

wow this reminds me of the old Open University programs with skinny bearded guys with massive glasses.

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Very useful. So an AFR gauge would not use an existing Oz sensor? In an AFR fitting kit, what's in the fitting kit part? How involved is it for a newb to fit?

wow this reminds me of the old Open University programs with skinny bearded guys with massive glasses.

 

Depends how adept you are with a set of spanners, a drill and a welder. Judging from the questions you've asked, I would recommend getting a pro to fit it for you as it's not the easiest thing to do as you need to weld a boss onto the exhaust for the wide band oxygen sensor to. (Wideband oxygen sensors are accurate over a wide range, usually 10:1 through to 19:1. The stock "narrow band" sensor is only accurate at 14.7:1.

This isn't a problem as the ECU only needs to know if it's at stoichiometric - 14.7:1 or leaner or richer. It doesn't need to know the exact value, which is what a Wideband Oxygen (WBO2) sensor will tell you)

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Very useful. So an AFR gauge would not use an existing Oz sensor? In an AFR fitting kit, what's in the fitting kit part? How involved is it for a newb to fit?

 

The stock O2's are a narrowband and can only measure within a very small area (13.0 to 15.0 or somthing like that) so are not suitable.

 

The AFR gauge kit will come with a O2 wideband sensor which can measure a much wider range (typically 10.0 to 18.0). This sensor needs to be mounted into the exhaust pipe around 30 inchs from the turbo. most aftermarket cat back exhausts come with an O2 boss welded into the 2nd cat back where the wideband sensor can be mounted. If you don't have one then you need to get a boss and have the 2nd decat drilled and the boss welded to it to fit the sensor. Most kits contain the boss too (if not I have one here you can have).

 

If you already have the boss welded on it's a pretty simple job to install the gauge and sensor provided you have a good set of axle stands and basic electrical skills (e.g can use a soldering iron)

 

Edit - bugger, too slow as normal!

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Depends how adept you are with a set of spanners, a drill and a welder. Judging from the questions you've asked, I would recommend getting a pro to fit it for you as it's not the easiest thing to do as you need to weld a boss onto the exhaust for the wide band oxygen sensor to. (Wideband oxygen sensors are accurate over a wide range, usually 10:1 through to 19:1. The stock "narrow band" sensor is only accurate at 14.7:1.

This isn't a problem as the ECU only needs to know if it's at stoichiometric - 14.7:1 or leaner or richer. It doesn't need to know the exact value, which is what a Wideband Oxygen (WBO2) sensor will tell you)

 

Damn thats well explained. I get it now.

 

what about the actualy unit? What manufacturers do you recommend? I will need to mount a gauge on a pillar right? Or have it mounted. What makes do people have on their cars here?

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The stock O2's are a narrowband and can only measure within a very small area (13.0 to 15.0 or somthing like that) so are not suitable.

 

The AFR gauge kit will come with a O2 wideband sensor which can measure a much wider range (typically 10.0 to 18.0). This sensor needs to be mounted into the exhaust pipe around 30 inchs from the turbo. most aftermarket cat back exhausts come with an O2 boss welded into the 2nd cat back where the wideband sensor can be mounted. If you don't have one then you need to get a boss and have the 2nd decat drilled and the boss welded to it to fit the sensor. Most kits contain the boss too (if not I have one here you can have).

 

If you already have the boss welded on it's a pretty simple job to install the gauge and sensor provided you have a good set of axle stands and basic electrical skills (e.g can use a soldering iron)

 

Edit - bugger, too slow as normal!

 

Thanks Homer, thats kind of you, I know I have a double decat and a greddy racing exhaust but, even though I can solder, I would not be comfortable with Jacking car up and doing the work. Will look into getting some one to help , after I have purchased an AFR, and the fitting kit.

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Thanks Homer, thats kind of you, I know I have a double decat and a greddy racing exhaust but, even though I can solder, I would not be comfortable with Jacking car up and doing the work. Will look into getting some one to help , after I have purchased an AFR, and the fitting kit.

 

No problem Carl. As you're fairly new to this it's probably best you get it professionally installed. As Tony mentions, the AEM and Innovative ones are the most popular, and for good reason.

 

I would recommend Phoenix in Watford or Whifbitz in Enfield for the installation.

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No problem Carl. As you're fairly new to this it's probably best you get it professionally installed. As Tony mentions, the AEM and Innovative ones are the most popular, and for good reason.

 

I would recommend Phoenix in Watford or Whifbitz in Enfield for the installation.

 

 

Thanks Homer, I'll bear that in mind. Any one had the PLX DM100

installed with the AFR sensor module? Thought it would be good as I can set up warn zones, and I can focus on the road, and check out values later. Not sure if its as accurate as a traditional gauge though.

 

http://www.plxdevices.com/products/dm100/

 

 

Hi Carl where abouts in Herts are you?

If not too far from me, then you are welcome to pop over or we can meet somewhere and you can have a look at my 'Wideband' install and set up.

Also get a first hand demo and I can help you get it done if you like.

 

Wow, thanks. I'm in Watford. Where abouts are you? That would be great.

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Have to jump in here and put in my preferred wideband setup, any of the Innovate range LC-1 being the simplest install, and the LM-1 if you want data logging, all very useful and the Innovate gauges have a better range when things go really rich, the AEMs wont go that low;)

Just to add that oxygen sensors, be it wideband or narrow band, which has already been explained, work by measuring the amount of unburnt oxygen in the exhaust gasses, and the AFR reading reflect this, people have already mentioned the figures etc, but what they haven't said is the air/fuel mix is used to make power but also adjusted by the ECU to be economical and emission friendly, ie the 14.7 AFR but also to cool the combustion process in high boost areas ie 9.0 -10.5 AFR readings that the Supra commonly produces, but unfortunately this is not so good for power, hence all the fuelling tweaks that are commonly used.

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Have to jump in here and put in my preferred wideband setup, any of the Innovate range LC-1 being the simplest install, and the LM-1 if you want data logging, all very useful and the Innovate gauges have a better range when things go really rich, the AEMs wont go that low;)

Just to add that oxygen sensors, be it wideband or narrow band, which has already been explained, work by measuring the amount of unburnt oxygen in the exhaust gasses, and the AFR reading reflect this, people have already mentioned the figures etc, but what they haven't said is the air/fuel mix is used to make power but also adjusted by the ECU to be economical and emission friendly, ie the 14.7 AFR but also to cool the combustion process in high boost areas ie 9.0 -10.5 AFR readings that the Supra commonly produces, but unfortunately this is not so good for power, hence all the fuelling tweaks that are commonly used.

 

Enlightening. Looks like this one is the one you have and may be all I need:

 

http://cgi.ebay.co.uk/Innovate-G2-or-G3-Gauge-with-Wideband-controller_W0QQitemZ330178453673QQihZ014QQcategoryZ72205QQcmdZViewItem

 

I've looked into the PLX range of devices, and while I've not tried them, they do use the a bosch wideband sensor which is very similar if not the same as the aem version.

 

Hmm, then maybe PLX is the one I need becuase theres not much difference in price and it seems to be so flash, and upgradable.

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Enlightening. Looks like this one is the one you have and may be all I need:

 

http://cgi.ebay.co.uk/Innovate-G2-or-G3-Gauge-with-Wideband-controller_W0QQitemZ330178453673QQihZ014QQcategoryZ72205QQcmdZViewItem

 

 

 

Hmm, then maybe PLX is the one I need becuase theres not much difference in price and it seems to be so flash, and upgradable.

 

The main reason I like the PLX range is because of the modular approach as well as the simple display options, I personally don't want a dash full of gauges, I'd rather just have one or two that display all the info.

 

The PLX OLED is great for that, DM-200.

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The main reason I like the PLX range is because of the modular approach as well as the simple display options, I personally don't want a dash full of gauges, I'd rather just have one or two that display all the info.

 

The PLX OLED is great for that, DM-200.

 

Gav does the supra have an OBD II port? It says the DM-200 needs that, or the one that I was thinking of getting...

 

Thanks,

 

Carl.

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Gav does the supra have an OBD II port? It says the DM-200 needs that, or the one that I was thinking of getting...

 

Thanks,

 

Carl.

 

No point in getting the OBDII version, the supra doesn't have anything like this (well not the the pre-facelift). There is a DM-200 which doesn't have an OBDII connection.

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