soros151

Hi, Mild noob here :? trying to understand the basics of tuning, and with it the lessons on A/F ratios. I want to know how does the A/F ratios affect so much and how do they work. Also what does it mean 11.5 AF and those things? I know chemistry is involve but, please bear with me. :D

Joe_Dezod

Air fuel ratios are one of the most important tuning aspects of any engine, followed by ignition timing. Air/Fuel ratio is for every x amount of fuel, there's x amount of air. 12 parts of air, for 1 part of fuel basically

There's a fine line of tuining with air fuel ratios to get the most reliable power out of your car. Tune too rich and you foul your plugs, and loose some unnecessary power. Tune too lean and you're running too hot and risking severe damage to the motor.

When we tune for example... We like sitting around the 11.5 range, going as high as about 12.2. 12.7 is about optimal for a boosted car but for a daily driven tC with 10+ psi it may not be the best option. The 11.5 can help cope with a boost spike, or some really hot days. This will lower the chance of detonation which is usually the result from poor fuel or ignition maps.

Ignition maps adversely affect fuel. If you advance ignition timing, you effectively leaning out your fuel curve to a certain extent because the spark is starting an "x" amount of degrees sooner. Retarding the ignition timing will effectively enrichen the fuel curve because you're starting the spark sequence later.

If you have more questions please ask because Paul and I haven't been flexing our minds too much outside of our S2 engine management system haha.

soros151

What are the steps on tuning a car with engine managements, and what would be some of the basics concepts when tuning. Like tips when trying to tune or learning about it. Something that comes from experience. Also when looking for an engine managements what are the requirements you would think help the most, like if there is an unnecesary part of the engine management that we may never use. How do you know that a basic configuration on the A/F map on your engine managment is an appropiate one to start with, like what would be a basic maps, like our cars? Is there such a thing? Sorry for all the questions.

Joe_Dezod

It's ok I just went through all this with another member on AIM so it's definately fresh in my head.

I'm going to make a MASSSSSSSSSIIIVEEE post. I'm working on it right now. It'll cover every aspect of info, including what you're asking now. I'm going to do this so that I can save time for other members and myself, and help get everyone up to speed on what the fundamentals are for a boosted toy

soros151

Yay :D thanks for everything, you guys are da BOMB!!!

kytc

^Dezod knows their stuff and they're a good bunch of guys, I'd SERIOUSLY consider them for a turbo if I didn't already have a s/c

paul_dezod

Just as an FYI with respect to air fuel ratios and tuning as well. The typical rule of thumb on AFRs is as follows:

11.5:1 approx rich best TQ @ WOT
12.2:1 safe best power @ WOT
13.3:1 approx lean best TQ

Every motor responds different, these are, for the most parts, the essentials of AFR

johnnywebb

hmmm. i remember looking at the Intake shootout thread, and the dyno charts were all looking at how the intake affected A/F based on a 14:1 standard... why?

kytc

^14.7:1 is stoichiometric a/f ratio

paul_dezod

Correct.

We have discovered that where the MAF reads effects the AFR.

Gases flow faster to an extent in smaller diameter tubing.....Gases flow slower in larger diameter tubing.............Assuming all other factors constant.

The faster velocity gases make the MAF read higher thinkin more air is coming in, and it will automatically add fuel. Vice versa with a larger diameter.

Hence why AFRs were more rich with a 2.5" intake versus the 3"

Joe_Dezod

the BIGGGGG thread is almost done guys stay tuned

pryde

Dezod... I love you guys. I have been trying to find some info on my own for awhile and couldnt seem to make any head way. Any more info you guys can post will be awesome. If i might add a question: I live in colorado... kinda wondering how elevation effects all of this. If you could inject some basics figures on how elevation effects AFR it would be awesome!!!

Joe_Dezod

Post is done.

Thanks for the love.
https://www.scionlife.com/forums/viewtopic.php?t=125753.

Atmospheric pressure will theoretically alter your tune. The MAF will actually help compensate for this so the change should be very minimal. The MAF will see that less air is going into the motor. Under WOT, it's a fixed tune, so a SLIGHTLY richer tune may be noticed, but it's better to be slightly richer than slightly leaner

pryde

Hmmm. What I have heard in the past lead me to believe that the difference was signifigant. This is good to know.... again you guys are awesome!

DTRUONG_112

too rich results in foul plugs. What does a foul plug look like?

soros151

Found this, maybe it is. I don't know

paul_dezod

Pretty much!

hPower

Excellent thread, so good to venture beyond the typical intake/exhaust thread topics once in a while. Thank you for the great info Paul.

sallad

good stuff, I am a supercharged gou running 9.5 lbs, and at redline in 4th gear I was at 11.1 a/f