Mixture Control at Wide Open Throttle (WOT)?

[magnuman]

I just finished a mixture control mod. for the Hemi, but am not absolutely sure it will work. It should work any time the fuel injection is in the open loop mode, but I am primarily interested in open loop at WOT. At WOT the fuel injection is in the open loop mode and the oxygen sensors in the exhaust are not monitoring the mixture. In the closed loop mode they do, and force maintain the mixture at 14.7:1, which is chemically perfect for combustion and near optimum for emissions. Between 12-13:1 is optimum for performance. My mod. is a linear potentiometer that is adjustable from 0-50,000 ohms(which is the approximate range of the IAT) and is hooked up in series with "signal lead" of the intake air sensor (IAT). When in the "0" position (and in normal driving) it reads the sensor at face value, which is true intake air temp. Crank it all the way on (or somewhere in between) just before you're going to do a WOT blast, and the PCM computer thinks the intake air temp. is around 10 degrees F, and should then richen the mixture at WOT.....hopefully to the 12-13:1 air-fuel ratio. Right after the WOT run, the pot. must be turned back to "0" or the PCM will start tracking the readings and begin its adaptive corrections. My "Holley Bible" says that there is about a 4% difference in mixture requirements for every 11 degrees F change. I think it will work better in hotter weather than when cool, because of the larger temperature difference. My preliminary figures indicate that it will have to be set 43 plus or minus 7 degrees of true ambient to get the correct mixture. I have taken resistance readings of the IAT at 32, 40, 60, 80 and 120 degrees, so I will have some idea what to set the resistance at. Any comments or input on whether members think it will work are appreciated.

[JMatt]

It works. See my track results in the SRT-8 forum. Use a 10K pot though. 50K is too much.

[magnuman]

JMatt,
Since we had discussed this I have added a switch to mine to go rich or lean. My adjustments with the 50K pot. are obviously not as "fine tuned" as yours Which way are you going....richer or leaner?? How much different from ambient are you going to get your best results. (I know it will vary from day to day) I've still not done enough runs with mine, but have also gained about two tenths last fall. As I recall, I was going leaner...set about 20 degrees hotter than ambient. Let me know, as I am headed to the races in a couple weeks.
Also, did you try it without using the pot??

[JMatt]

I have headers and Magnaflow cat-back. This made my system lean out. I'm adjusting the temperature down, in order to richen the mixture. With a 10K pot, I lower the temps from 20-30 degrees depending on the initial reading. Also, I relocated my IAT to the air box from the intake, in order to get consistently lower readings (i.e. closer to real world and not affected by engine temp) before engaging the pot.

I only ran one time without using the pot, and the time was slower, but still in the 12.9's. I didn't do enough testing with and without.

[magnuman]

How much difference did moving the IAT sensor to the airbox make in readings? I would think that might help a little also. Good idea.

[JMatt]

The big difference is the sensor "recovers" to reading real world intake temperature much quicker than when its sitting practivally on the intake manifold soaking up heat. This makes a big difference in the staging lanes. With outside temps around 50, I would read 75 in the staging lane. The other SRT-8 would read 110.

[vvv90]

Originally Posted by JMatt

The big difference is the sensor "recovers" to reading real world intake temperature much quicker than when its sitting practivally on the intake manifold soaking up heat. This makes a big difference in the staging lanes. With outside temps around 50, I would read 75 in the staging lane. The other SRT-8 would read 110.

JMatt you're the first person to give the REAL reason for IAT relocation! Most people think it will increase HP across the board. The coupling around my IAT in my 'Vette was made of thick steel . I immediately replaced it with a plastic one.

[magnuman]

Where on the airbox did you mount it and did you drill a bigger hole and use a rubber grommet?? Is it still in the airflow? I think I feel another mod. coming on....real soon. Any pictures?

[artichoke]

Originally Posted by magnuman

... In the closed loop mode they do, and force maintain the mixture at 14.7:1, which is chemically perfect for combustion and near optimum for emissions. ...

I thought that the mixture in normal driving (non-WOT) was supposed to be too rich, in stock configuration.

[vvv90]

Originally Posted by artichoke

I thought that the mixture in normal driving (non-WOT) was supposed to be too rich, in stock configuration.

It's the other way around. In closed loop 14.7:1 is the best anyone should see no matter what car, but the wide band output I've seen on WOT passes on dynos show 11-11.5:1 AFR's which is PIG rig for an N/A motor.