AFR & Boost...
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AFR & Boost... This has probably been covered but I didn't find anything in the search so here it is.....
What kind of AFR do you guys shoot for when in boost? I am mostly looking for people who are running 91 - 93 octane on the street.
What kind of AFR do you guys shoot for when in boost? I am mostly looking for people who are running 91 - 93 octane on the street.
I run 93 octane. At between 10-15 lbs of boost I keep it between 11.0:1 and 11.5:1. I will also be curious to see what others say, since I have never been on a dyno and tune my truck myself.
11.5/1 above 5000 rpm is pretty much standard. Bob
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I also target 11.5 but feel good about a log if the entire pass is 11.0-11.8. Your AFR reading also depends on how far back the sensor is in the exhaust system. Typically the further forward it is, the richer it will read. So if you see 11:9-12:0 with a sniffer in the tailpipe, that should be 11:5-11:6 up by the turbo.
I personally would never get a tune at a place that sticks the air/fuel sniffer in the tailpipe. The sniffer in the tailpipe can be very unreliable. If an exhaust system is not 100% welded, air can suck in at the joints under wide open throttle and will throw off the readings, and you just never know how much it is being thrown off. Bob
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I might have to get a extra wideband, install it in one of the rear O2 ports and compare the 2 readings........
Lean or rich? I've had the wideband in both locations and didn't see a difference, I also question how accurate the common widebands are when you get into the 10.0-11.5 afr range. Not disagreeing with you just questioning if what we use is that accurate. My wideband was $300 range and I here about the pro's using $3000+ setups.
i use an AEM, and my best Friend with similar setup uses INNOVATE LC1 , and we have an LM1 hooked up also.
When under part/normal throttle conitions when the exhaust was actually flowing somewhat like it was supposed too, i noticed ZERO differences, when WOT, i would consistantly read between 1.0 and 1.3 RICHER when the wideband was placed in piping PRE turbo. This is not good. So, when i was thinking i was in the 11.0 range i was actually closer to the 12.0+ range.
All three rearmount cars i have been around and had a hand in building or help build have done this. so i see 3 out of 3 as a sign that it should be placed in the tailpipe POST turbo.
Not to mention the numbers are very inconstant and not steady when the wideband was place pre turbo, it was very difficult to get the afr to settle into a consistant area, the reading wanted to jump around alot more when preturbo.
When under part/normal throttle conitions when the exhaust was actually flowing somewhat like it was supposed too, i noticed ZERO differences, when WOT, i would consistantly read between 1.0 and 1.3 RICHER when the wideband was placed in piping PRE turbo. This is not good. So, when i was thinking i was in the 11.0 range i was actually closer to the 12.0+ range.
All three rearmount cars i have been around and had a hand in building or help build have done this. so i see 3 out of 3 as a sign that it should be placed in the tailpipe POST turbo.
Not to mention the numbers are very inconstant and not steady when the wideband was place pre turbo, it was very difficult to get the afr to settle into a consistant area, the reading wanted to jump around alot more when preturbo.
Last edited by JAX04; Sep 17, 2010 at 09:38 AM.
It would be nice to hear an explanation on why and how different pressure ratios affect the wideband. I run mine in the midpipe (rearmount) but I also run 10.5afr's and spray 100%meth starting at 4lb's.
I tuned my WOT by richening up the car to the point it started breaking up or just ran flat and than leaned it out to get my 10.5afr.
It's a geat tool I just like to verify that when the WB says pig rich the car runs pig rich and pull fuel from there.
I tuned my WOT by richening up the car to the point it started breaking up or just ran flat and than leaned it out to get my 10.5afr.
It's a geat tool I just like to verify that when the WB says pig rich the car runs pig rich and pull fuel from there.
The explanation is that wideband O2 sensors are affected by pressure, period. You want them in the pipe that doesn't have high pressure for the most part which is after the turbo.
If that's the case then every wideband is affected, anytime a gas has velocity there is pressure.
Air and fuel compressed you will have a greater density of fuel.....fuel dont compress just air does. So if your reading the amount of air and fuel in one space.. I dont think the wideband knows that the air is compressed, it just see the volume of space it is taking up....so you will see more fuel than air, even though you technically have more air there.