What is the ideal NA AFR - Tuning Forum

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What is the ideal NA AFR
Thursday, September 21, 2006 8:19 AM
So for about half my rpms I really dont make boost so im like every other NA cav, im currently working on my VE what is the ideal AFR to try to hit until I start making boost, I see that the stock file has the AFR set for power enrichment at 13.0 all the way to 3600 then dips into the mid 12s after that, is there some magic number to try to hit for NA like 12.8 or something, i know what to hit under boost, i just want to make as power as I can without being wasteful before I get there



1989 Turbo Trans Am #82, 2007 Cobalt SS G85






Re: What is the ideal NA AFR
Thursday, September 21, 2006 4:19 PM
every engine will be different, where it makes the most power and has knock resistance. You really need to dyno tune to ensure timing and afr changes are making positive effects.


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Re: What is the ideal NA AFR
Thursday, September 21, 2006 4:54 PM
well under boost 11.8 seems to be the magic number as soon as it touches above 12 it starts getting knock retard, i never get knock out of boost and im running the PE mode stock at the 13.0 AFR in the range out of boost



1989 Turbo Trans Am #82, 2007 Cobalt SS G85





Re: What is the ideal NA AFR
Thursday, September 21, 2006 11:49 PM
You can do quite a bit of tuning on the road. I don't believe that every engine responds differently until you really get to the finer points. I do believe that you need to tune using both timing and fuel to get maximum efficiency and power. If your AFR reading is from a good wideband (never forget that a wideband can fail like any other piece of equipment) then you should look at reducing timing and increasing AFR (Increasing AFR means going from 11.8 to a higher number, say 12.2). Honestly, you want the leanest fueling you can safely and reliably get which still makes suitable amounts of power.

I still haven't seen anything on acceleration enrichment with HPT. You may have no ability to adjust AE. But generally, with larger injectors the AE shot gets too large. You might not notice it in the seat of your pants but you'll see it on the WBO2 gauge as a very rich surge in AFR. If you have an EGT gauge then you'll see it as a slow increase in temperature.

If you have an EGT gauge it will be handy for tuning, especially in a situation like this. The turbo is "powered" by the heat released in the exhaust. If you make no boost, then your exhaust temps are probably too cold. The EGT gauge would answer that question quickly.

A general rule to start with is 2 deg less advance for every psi of boost. If your timing curve is nowhere near that you may want to spend some time developing a test map which retards timing a bit faster.

-->Slow
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