Optimal A/F for an FE
 

Can anyone give me some general guidance as to the best A/F ratio of an FE?

I have stage 3 heads on a 427 built by Keith.

len

It's debatable; but I'll open this show with a wager of 12.8:1 to 13.2:1 and reference this article: http://www.carcraft.com/techarticles...ter/index.html

WOT 12.2 idle 13.9

12.8 to 13.1 for max power at WOT, normally aspirated. 13.XX to 14.XX @ idle to part throttle/cruise.

It's not that simple as 2 numbers
 

kobrabytes Len The general numbers are 12.7-12.9 to make the most torque. 13.1-13.4 make the most HP Idle or light cruising you want in the 13.7-14.1. The problem is that EVERY MOTOR likes different things when running. There are a bunch of guys on the forum running now 482 motors. They all have KCR stage III heads and same cams, compression, carbs and intakes, basicly similar motors. These motors all have different sweet spots for maken the most Torque and HP. It may vary by 25 rpms or 300 rpms. Another thing is Location, location, location. 300 ft above sea level against 700 ft. Could have same specs and be 10-15 HP differents and 8-10 ft of torque. How clean the air is, this is a biggie.%/ I don't know where you live but there is a big different between my town and 10 miles away in E-town. In the evenings the air is heavy and the cars run faster. The best thiing for you is to try and find a good dyno shop and have them setup your motor for the best specs. I have my car setup for 90 degree days and 80% humitity. I run it a little soft because I am not looking for every last HP out of my motor. Timing is another big thing with how much and when it comes in. Some motors like 40+ degrees, others like 34-36 total. Same motor with the same specs. Spark plugs and the gaps of them. .002" can make a differents in power of the motor. Heat ranges also make a differents, some motors like colder plugs, some like hotter than the standard range of our motor. I run 1 range cooler. I am not trying to confuse you but all these things change the way each motor runs. I am a wrench for over 30+ years, to me a motor is a living, breathing thing, and talks too. The hard part is understanding what it wants.%/ The best info I can give you to 2 things. First off Buy a good LM- meter to read both banks of the motor with a datalogger. If you want to try and do your own tuning, make sure you have a backup file to return to where you started if the motor gets upset. You will also down the road, depending on where you live have 3-5 programs for different times of the year if you drive 3 out of 4 seasons. You can go crazy with the tuning issues with FI. If money was not a issue, there is an 8 O2 sensor recorder for each cylinder and EGT with the same ability to record the motor working. If you have a system that can controll spark and fuel to each cylinder, you can really fine tune a motor for max power. Each motor has weak and strong cylinders, this is cause by, ports not being the same size, location of the cylinder, firing order, flow ratings being little different, the intake manifold not being ported to match all cfm equally. Some manifolds are 10-30 cfm off from each other. This is why I recommend Joe Craines services for intakes. He will match the flow to within 5-8 cfm on most manifolds. I have seen the beautiful work he does. Motors also run better. Some pick up 3-5 HP others pick up 15-18 hp. these are REAL numbers, not bench racing specials. Matching ports in and out of the heads, intake and exhaust manifold is a magic that the pro know and do. The other thing is a Bigger port is NOT a better port for power. It's about matching parts.%/ I hope this explains a little about what you are trying to do and why somethings either work or don't work. It is not to hard to get your motor in the ball park and setup with the A/F, but to have it razor sharp takes alot more work.:) Side note to this, I was working on my tuneup of the 482 motor, the O2 sensor was not reading the correct A/F numbers, I burnt the paint by the side pipes off the body in 30 seconds.:eek::CRY::( I also run a soft setup with timing and A/F readings. Rick Lake

I believe it depends on if it is carb / EFI / Webers

Also, are you looking for max power, drivablility ???

Len,

This is a tricky question to answer as the the AFR selection is about more than just performance. Fuel is also a coolant so rich mixtures can be important in certain circumstances (this is why a supercharged or turbocharged engine is typically set to target 11.xx-1 AFRs for example). I would say that 12.7:1 or so would definitely be safe for most naturally aspirated street driven engines and this would be a good place to start for a WOT AFR. This would be on the side of "rich best torque". I think that the FE's that Keith builds seem to like a leaner mixture than this (Keith had mine tuned for a 13.6:1-13.8:1 AFR at WOT; I am running EFI with a 482 ci FE, stage 2 heads, and one of Keith cams). My exhaust system is not as good as Keith's dyno headers in terms of flow so I have adjusted my WOT AFR to be a little richer 13.1-13.3 while I retune the engine to better match the exhaust on the car. This is still on the lean side and would be considered "lean best torque". Also keep in mind that the choice of AFR will effect your ignition timing requirements at full throttle as well so you want to approach the lean limit VERY carefully. The only way to be ger these settings to their optimal values for a given motor is to dyno the motor with a load bearing dyno and an exhaust setup with per cylinder pyrometers so that you can see what is going on with both torque output, AFRs, and EGTs (Exhaust Gas Temperatures). Almost no one has this sort of setup so the next best approach is to use a load bearing dyno (best is to use a chassis dyno so you can calibrate with you actual exhaust system). At cruise levels (light throttle), I would aim for 14:1 - 14.7:1. In an EFI setup, you would typically blend WOT settings into the light throttle settings as throttle is rolled in for acceleration. The attached is my current AFR table that is in my EFI setup. NOTE THAT NO ONE SHOULD COPY THIS TABLE AND JUST USE IT - THESE SETTINGS ARE NOT APPROPRIATE FOR EVERY MOTOR AND WHAT WORKS FINE IN MINE MAY VERY LIKELY DAMAGE YOURS.

http://www.clubcobra.com/photopost/d...edium/AFR1.jpg

It should give you some idea of what the final curve should look like. AGAIN, START ON THE RICH SIDE (say 12.5:1) and only lean it out if you have the equiment to accurately measure what you are doing. Are you using a carb or EFI? Also, what does your motor have in terms of a cam and static compression ratio?

I hope this helps you,

- Fred

Thanks for all of your inputs!

My compression is 10.5:1

Running TWM with FAST.

When Keith originally set up my engine he used Speed density. I lacked enough vacuum to run in speed density well. I've now got the FI in Alpha N mode and it runs pretty well. Just dialing the power back in. I'm at the point where I probably need to get it on the dyno, although I still am doing some tuning based on what I seed from a logging session.