A/F ratio's before and after Chip.

[08snake]

I just received my Amazom Racing Diablo Delta Chip from Rick and was wondering what change in A/F ratio I can expect. There is only one dyno on Island that has Wideban Sensors so my next dyno wont have that. The chip should be setup to the mods in my sig. Any ideas?

 

[CWCobra]

ttt

 

[Smrgol]

Here's what the chip did according to some Autotap data logging:

I need to do it again with my new exhaust. Also, the wideband at the dyno I use, which sniffs at the tail pipe, shows the same shaped curves but about 0.5 to 0.9 leaner.

 

[08snake]

I'm obviously a rookie at this. The lower the number the richer?
Ideal would be around 11 or 12:1? All I have is exhaust and CAI.
Should I expect curves close to this? Sorry about so many questions, just concerned about A/F ratio since I dont have the ability to check it on a dyno.

 

[Smrgol]

Yep, the lower the number the richer the mixture.

Just some background fyi. You'll hear the term "stoichiometric" occasionally. That is the ratio of air to fuel at which all the air and fuel are consumed completely leaving only by products. That ratio for gasoline is 14.7:1. This ratio is optimum for fuel economy and emissions because you are, theoretically, leaving no unconsumed fuel nor creating any extra byproducts from excess air. The PCM in closed loop mode attempts to maintain the car at this ratio, on average.

The best power, however, is actually found with a richer ratio, due to buffering and other chemical engineering issues that I'm still figuring out. Every car is different and every motor design different, but for Mustangs with 4.6's optimal power is actually found between 12:1 and 13:1. I think I saw a chart once that put the average at 12.2:1 but I've lost that link.

I think the max is 12:1. Depending on altitude and other factors you could go leaner but you are at the mercy of the fuel, timing, and intake systems. For that reason most folks I've talked to tuning reliable street cars typically stay well below 12:1 just to provide some safety margin in case something wierd happens, like a hose gets loose and lets unmetered air in. It's easy to find and fix things like that but at the ragged edge it can cause massive detonation. With a little safety margin built in the PCM has time to warn you and you have time to fix it before breaking something major.

On the pre-'03 motors with stock internals I think most "safe" tunes are between 10:1 and 11:1 to be really on the safe side of detonation.

 

[ronreid03]

DWTALSO,

How did you use Autotap to generate that graph?

Thanks,

Ron

 

[Smrgol]

OBDII provides an output for the O2 sensors that is percent lean/rich with respect to stoichiometric. The value is negative if the sensor reads leaner than stoich. and positive if the value is richer than stoich.. So, a little math produces the measured AFR:

AFR = 14.7 * (1 - (P/100)),

where P = the percent lean/rich.

 

[Rick@Amazon]

Hey Bo, You should see around 11.1 to 11.4 with the chip. As far as using a 02 sensor voltage to monitor a/f please be carefull for it is very inacurate. The sampling speed of the EEC is not fast enough to get a quick enough reading before damage accures. This is why cars that run lean don't last because the EEC can't react fast enough. This is why you should always use a wideband 02 with a high sampling rate (20 times a sec or better). I have use a Autotap and the are they very nice for the money.
dwtalso another good way to keep tabs on the A/F is to watch the long term and short term fuel trims on your Autotap. These can be very helpfull with tuning. It tells the tuner at what point he needs to add or subtract fuel. You can see some interesting things when you datalog it on your Autotap.
Hope I could help
Rick

 

[Smrgol]

Originally posted by AmazonRacing
Hey Bo, You should see around 11.1 to 11.4 with the chip. As far as using a 02 sensor voltage to monitor a/f please be carefull for it is very inacurate. The sampling speed of the EEC is not fast enough to get a quick enough reading before damage accures. This is why cars that run lean don't last because the EEC can't react fast enough. This is why you should always use a wideband 02 with a high sampling rate (20 times a sec or better). I have use a Autotap and the are they very nice for the money.

Good points. I use data like this to see trends and large changes. For example, in my chart above it's pretty clear what the chip did to the overall AFR curve. Diagnosing smaller transient signals requires a different device for sure.

dwtalso another good way to keep tabs on the A/F is to watch the long term and short term fuel trims on your Autotap. These can be very helpfull with tuning. It tells the tuner at what point he needs to add or subtract fuel. You can see some interesting things when you datalog it on your Autotap.
Hope I could help
Rick

Yep, I've got my Autotap config files set up to grab those data too. The LTFT are especially interesting since the PCM uses those to modify that AFR curve during WOT. So far, my LTFT's have remained fairly close to zero since the chip went in. I need to check that now that the new exhaust components are installed .

 

[ronreid03]

Thanks for the response. That's what I like about this forum: seems for every issue, someone's got experience and an innovative approach. I've got the autotap but it never dawned on me to use (I assume) the STFT's this way.

Ron