well my vortech is going to be installed soon and i have a couple questions regarding the air fuel #'s. I kind of have a basic idea based on the thread https://g35driver.com/forums/showthr...ighlight=gauge posted by g352nv a long time ago. So basically on idle, it should be around 14.7 and then go richer as i go into boost correct? Idealy, I would want it to be around 11.5 at full boost right? So since it gets richer as it goes into full boost, then the lower the number the richer it gets and the higher the # the leaner it gets? Generally, is the air fuel ever really off and how significant are a few decimal points? For example.. what if my car idles at like 15 or 13? It is going to be running off the SS box but the previous owner may have tuned it according to his car so i'm not sure what i'm going to expect. Of course im going to get my car tuned afterwards but I just wanted to get a better understanding while i'm waiting for it to be installed.

 

Your understanding of the numbers at idle and under boost is good. Your numbers will never be constant. Lower means less air to fuel, so richer. Higher means more air to fuel, so leaner.

Your AFR gauge will dance around like a light show and it takes some getting used to. At idle it can vary by +/- .5 or more. While under boost you won't stay right on 11.5 either. You might be under 11. You really want to stay under 12. While cruising you should also be around the same as at idle.

 

what values are known to be in the danger zone? Just over 12? Im guessing it matters a lot more during boost than it does when the car is just idling right?

 

The reason you want a lower AFR under boost is because of the heat at that time. The lower AFR can create moisture during normal conditions which is the reason why you want your AFRs higher when not under boost. From what I've seen, anyone that was experienceing AFRs over 12 under boost either had their car re-tuned to fix it or did some other investigating to find out why.

 

I wouldnt go more than 11.5 at full trottle/full boost especially if you are on a stock block. I drop down into the 9.8-10.3 range then as I go to full boost stay about 11.3

12 is way too lean to be safe its just not worth the risk for the little extra power.

 

Depends on alot of things such as intake & exhaust, climate, fuel, weather, etc.. Your A&F is related to your PSI so keep both in check if your going to be doing any hard driving @ the tracks..

Yes thats how you read the gauge.. Because we're in cali our a&f are a little high.. so if you bought your ECU from some one in lets say NY you should probably get it re-tuned or also if the previous owner had more modifications to his vehicle you should get it re-tuned..

zazaracing is right.. i'd go around 10.5 - 11 at full boost.. keep in mind if you boost more you'll need more fuel & etc.. those are safe numbers..

also depends on the tuners and ECU for accuracy and no spikes

 

An understanding of flame propagation speed and how rich mixtures cool the combustion chamber helps one decide on AF.

http://www.faqs.org/faqs/autos/gasol...section-1.html
http://www.motorcycle.com/mo/mcrob/rt-fuel2.html
http://www.erc.wisc.edu/modeling/mul...g2000/deur.pdf
http://www.gfcombustion.asso.fr/ecm/..._Johansson.pdf

 

I stay in the low to mid 11's under full boost (~8psi). Normal driving is ~14-15.

 

i got it guys, thanks.

 

So, let's say your driving along and you notice that your a/f spikes, whether by hearing the detonation or by meter, what do you do to save the engine?

If the a/f dances around that much, how do you keep it from becoming dangerous before it's too late?

 

It dances around but the most critical moments are underload and WOT, the Innovate set up is perfect for this due to the dial and digital display.