The Mustang Forum for Track & Racing Enthusiasts

Taking your Mustang to an open track/HPDE event for the first time? Do you race competitively? This forum is for you! Log in to remove most ads.

  • Welcome to the Ford Mustang forum built for owners of the Mustang GT350, BOSS 302, GT500, and all other S550, S197, SN95, Fox Body and older Mustangs set up for open track days, road racing, and/or autocross. Join our forum, interact with others, share your build, and help us strengthen this community!

Ideal Air/Fuel ratio?

Sesshomurai

Hi,
When I got my car dyno tuned, the side exhaust was open and it had off-road H-pipe and muffler deletes.
The tuner showed me the A/F hovering around 11.5-11.9:1

I closed the side exhaust and put the GT500 muffs back on and my Torque app is reading 14.5-15.0:1 from the ECM.

Here's a log entry from Torque

http://www.gogridwave.com/boss-log.html

I was under the impression that A/F ratio above 12 is generally bad. Any ideas what might be going on here?
Also, is it bad to drive it under this condition?


I have larger longtubes too.

D
 

steveespo

Lord knows I'm a Voodoo Child
Moderator
3,752
1,223
Exp. Type
Time Attack
Exp. Level
10-20 Years
NY Metro
Darren
Your log is all idle and no load low rpm, the car will try to keep it in a 14.7 ratio for emissions during low load condition for emissions, this is normal. When you were on the dyno you were in WOT full load condition, 11.9 is good and safe, 11.5 is a little too rich but won't hurt anything. I wouldn't want to run the car on track leaner than 12.0, some drag racers tune leaner like 12.3-12.5. Not good for road racing where cylinder temps go to max and detonation is a problem. Also please run 50/50 93/100 octane on track for safety. 93 on the street is fine.
Steve
 

Sesshomurai

Thank you Steve. That is a great relief :eek: because I wanted to try the new tune with some spirited country road driving today (for the first time), but was worried.
I will head back out and take more logs.
 
2012Boss302 said:
Sorry for the ignorance but, what is "Torque?"
It is an Android (smartphone) application that allows you to datalog, view information from the OBD2 port (with a cheap Bluetooth attachment), record video and overlay data, view data on "gauges", and do a bunch of other stuff. I highly recommend trying it out if you have an android phone.
 
My A/F stays at 13.5 - 14 almost all the time, but I don't "Race" the car.. its around town and a few Spirited runs... I always figured, that the car is smart enough to know if the A/F gets out of wack and will throw up a warning on the display... But since I don't race the car, and only use 93Oct (since I have the track key), then I figured I don't have much to worry about in the A/F department...
 

steveespo

Lord knows I'm a Voodoo Child
Moderator
3,752
1,223
Exp. Type
Time Attack
Exp. Level
10-20 Years
NY Metro
rpm3dinc said:
My A/F stays at 13.5 - 14 almost all the time, but I don't "Race" the car.. its around town and a few Spirited runs... I always figured, that the car is smart enough to know if the A/F gets out of wack and will throw up a warning on the display... But since I don't race the car, and only use 93Oct (since I have the track key), then I figured I don't have much to worry about in the A/F department...

rpm,
Your car is stock correct? When tuned the tuners increase spark advance and richer the mixture to increase power. Also a CAI and headers/free flow exhaust increase the amount of air flow into the cylinders which is how more power is made. Ford tries to keep the mixture as lean as possible under most driving conditions for fuel economy and emissions, but at wide open throttle a different set of calibration tables are used. Try logging a true 10 second full throttle run and I think you will see A/F ratio of 12.5 or so. The Track Key does some funny things with spark timing and fuel curves to get the lopey idle and engine braking, I think they run it too lean and that's why some people notice detonation with it. The good thing is the ECU will pull timing back when knock happens but that kills power. A good tuner will zero in e spark and fuel curves to make optimum power all across the RPM range, email tuners will do this for the most part and then back off timing a bit and richer the mixture a bit for safety.
Sorry for the long rant, but there is no "magic air fuel ratio" for all Boss engines, operating temperature, fuel quality, ambient air density and intended track use all play a part in a tune.
Steve
 
Yes its stock with exception to the Borla ATAK exhaust and MGW Shifter... so I should have nothing to worry about... I do need to reset the PCM as I drive with the Track Key 99% of the time and have noticed that its not a "Responsive" as it used to be.

Just gota disconnect the negative terminal for 10 minutes, then connect it back up, and let it idle with the Silver key for 5 minutes and all should be good again...
 

Sesshomurai

steveespo said:
.... Try logging a true 10 second full throttle run and I think you will see A/F ratio of 12.5 or so.

...
The Track Key does some funny things with spark timing and fuel curves to get the lopey idle and engine braking, I think they run it too lean and that's why some people notice detonation with it. The good thing is the ECU will pull timing back when knock happens but that kills power. A good tuner will zero in e spark and fuel curves to make optimum power all across the RPM range, email tuners will do this for the most part and then back off timing a bit and richer the mixture a bit for safety.

Steve, you are a sage. I'm learning quite a bit on this. I was monitoring my A/F from Torque while driving and when I slammed the throttle (for only short bursts) I did see the A/F go down to 12.4946. I saw 11.9 on the dyno, but I suspect that at higher RPMs and speeds perhaps this number creeps down further.

However, your comment earlier about not running on a track leaner than 12 as me worried my A/F is still too high and I'm told running lean under hard conditions will hurt this motor beyond repair. Since I can't test on a track until I get there I'll have to get my tuner to assure me that the ranges I see now won't pose a problem when I get there. Will visit them in the morning.

Here's my final log with some brief full throttle runs: http://www.gogridwave.com/boss-log3.html

I only pushed the pedal to the floor for 5-10 seconds at a time but I don't see real high numbers in the throttle position PID. Not sure how to interpret that metric still.
 

Sesshomurai

If you have an android device (if not, get one), then get Torque pro:
https://play.google.com/store/apps/details?id=org.prowl.torque&hl=en

I use this OBD2 device:
http://www.amazon.com/gp/product/B006NZTZLQ/ref=oh_details_o00_s00_i00
 
I asked this question a few month's ago. I used to use hp tuners on a Ls2 gto before the boss. 14.7 used to be where you wanted to be but now that we are useing e-10 things changed.Shaun from AED gave me the beat answer. With e-10 you need to run just alittle bit richer than a few years ago. That is one reason we have widebands up front,not o2 sensors.
 

TMO Supporting Vendors

Top