Ford Focus Forum, Ford Focus ST Forum - Reply to Topic
Ford Focus Forum
HomeContact UsAbout UsGalleryDiscussion ForumsMarketplace

Go Back   Ford Focus Forum, Ford Focus ST Forum > Ford Focus Tech Discussions > Focus Tuning Chat > question regarding A/F theory

Focus Tuning Chat Discuss performance tuning options for your Ford Focus.

Search This Forum | Image Search | Advanced Search    
Ford Focus Tire & Wheels FocusFanatics Merchandise

Thread: question regarding A/F theory Reply to Thread
Post Icons
You may choose an icon for your message from the following list:

Register Now

In order to be able to post messages on the Ford Focus Forum, Ford Focus ST Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Additional Options
Miscellaneous Options

Topic Review (Newest First)
09-24-2009 03:32 PM
thenorm to the OP. you should read up on lean burn engines. quite interesting in my mind. lean burn enginer run hotter. and hotter = more efficient from a thermodynamic point of view. however normal fuel injected engines run into detonation problems if its too hot. one way they get around this is fuel stratification. ie. the area around the spark is closer to stoichiometric and it gets leaner the further out and the area where the fuel is is cooler because of that fuel. the areas with little fuel can be hotter because there is nothing to ignite. this can be done by direct injection and theyr'e are other proprietary means the differ by manufacturer.
but, even these engines tend towards stoichometric when under heavy load, and lean out at cruising
09-24-2009 02:35 PM
1turbofocus I have made good TQ with them in the low 11`s and no issues , have found many respond to the added fuel very well

Now the Mazda just needs a good tuning solution like Diablo/SCT

09-24-2009 11:45 AM
Originally Posted by 1turbofocus View Post

The MS3 guys are learning the hard way that 12.6 isnt the safe AF as I told them that a few years ago , I build a few engines for the MS guys as well and play in them some

yes they do need to run meth to keep 12.6 safe. but that is indeed where best torque is made.
09-24-2009 11:38 AM
mlbbaseball ok, cool, that answers my question then, thanks!
09-24-2009 08:49 AM
Originally Posted by mlbbaseball View Post
makes sense, so if cylinder temp could stay at an ideal temperature, it would be safer to run a bit leaner?? i guess thats actually the gist of what i'm asking.
Yes , If that is what your asking then yes , If you could controle Cyl temp in another way other then adding more fuel then you could run it leaner

The MS3 guys are learning the hard way that 12.6 isnt the safe AF as I told them that a few years ago , I build a few engines for the MS guys as well and play in them some

Just because you inject the fuel directly into the Cyl under high psi does not change the AF ratio needed to keep it safe , Direct Cyl injection is more for emmissions and MPG more then anything

09-24-2009 01:12 AM
Originally Posted by mlbbaseball View Post

IF my logic is right, then a DI car can run a bit higher A/F ratio cause they can keep the temps cooler?
your logic is right, MS3's are often tuned to about 12.6 even at 22+psi...

start googling there is a LOT of info about the ideal max torque afr of different types of engines.

And then there is the real world which usually differs from that info, where single cam mustangs love to run at 12.6 but the NA 4v motors can get up above 13, and where turbo zetecs can be under 11.5 and still be happy.

bottom line is you have to either get on the dyno and figure out what works, or beg for the experienced opinion of a nice gentleman (sometimes named Tom)
09-24-2009 12:05 AM
mlbbaseball makes sense, so if cylinder temp could stay at an ideal temperature, it would be safer to run a bit leaner?? i guess thats actually the gist of what i'm asking.
09-23-2009 11:59 PM
1turbofocus I think your getting Cyl Temp and engine coolent temp confused , mixed , crossed

As you know you have 2 temps , engine coolent that cools the heat from the Cyl and Cyl temp , the more work (load) and engine does the more fuel it needs to keep doing it idle 14.7 , NA 13.0 , FI 11.5 big boost 10.5 all depending on the engine , It needs this fuel to help keep the cyl charge cool and to feed the demand for power/load , more air going in needs more fuel added

Actually the cooler the engine (engine coolent temp) is the less efficient it is to a point

09-23-2009 11:33 PM
mlbbaseball well, then i guess i'm asking, why do the A/F ratio's drop below 14.7 under WOT? i mean, i was thinking if the motor could stay maybe say at 100* F (just throwing a low number out there), or even less, then it could stay at 14.7 because the motor wouldn't get too hot, no timing would be pulled and no predetination. I've always thought that the most power would be made at 1.0 Lamda. (in an ideal state) but do to real world factors, motors really can't be run at 14.7:1 under load. so do to heat, we have to run the motors richer to keep them cooler.

the reason i was thinking this is because of all the new Ecoboost engines. they are turbo'd and direcet injected and i think they have some sort of VCT or whatever solenoid based valve control . DI motors have much higher fuel PSI and are sprayed directly over the piston crown much more evenly than in the zetec. thus helping to cool the piston and in return giving a more complete combustion. but since the fuel is helping to keep the motor cooler, i'm thinking they can run the motor a bit leaner safer.

I dunno, do u follow my logic?? I'm just curious and as i'm learing more about direct injection, it intriuges me. and i was just thinking that they can squeeze a bit more power out of them because they are able to keep them a bit cooler. even if only by a few degrees. but i think the theory still holds up, i'm not sure.

like i said, just curious!!
09-23-2009 06:23 PM
1turbofocus No , To cool of an engine wont make good power and will get very crappy MPG

This thread has more than 10 replies. Click here to review the whole thread.

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

All times are GMT -5. The time now is 11:10 AM.

Copyright 2002-2014 All Rights Reserved : Privacy Policy : Advertise Information

Focus Fanatics Ford Focus Forum offers many fun ways for you to engage with other Ford Focus Owners from across the world. Whether it be about the aftermarket performance modifications, technical how-to's, European tuned suspension or awesome fuel economy similar to the Cadillac ATS-V, Ford Fusion and Acura TLX. You can find all Ford Focus and Focus ST related information here. Join our Ford Focus discussion forums and chat with local Focus enthusiasts in your area.