14.7 is considered perfect for any engine under light load, but there are lots of factors involved. Tell us more about what you are doing. Welcome to the HAMB. -Abone.
As mentioned already, there are a lot of factors. E10 drops to ~14.1 E85 drops to 9.7 or 9.8 variable as all E85 is not 85% EtOH
Apropos of nothing, if you happen to be running Nitromethane a stoich ratio is 1.7:1. For a WOT blast fatten it up to 1.1:1!
Gasoline? Crusing with a blower motor? I'd say somewhere between 12:1 and 16:1. Make sure it drops to somewhere in the 11-13 range when you open the throttle. Carbs and blower motors are pretty forgiving about AFR. And you can drive yourself nuts trying to make "efi" numbers with carbs. If it's running good, not belching smoke, not coughing or sneezing, throw away the AFR gauge, and enjoy the drive!
On Gas , I prefer AFR 13.5- 15 cruising . 14.1 and higher create more heat , under boost wide open , I like. 12.0 - 13..ish . I also set my AFR on the leanest Cylinder you will need a Efficient cooling system with Blower / supercharger
When I see guys dyno test its usually targeting about 12.5:1 at WOT for a combination of safety and making power. I have a wideband in my more expensive engine car. Cruising I have it set up around 14, but it fluctuates some.
The wideband can drive you crazy if you stare at it. Especially cruise and idle ratios. "You *expletive* why were you 13.8 all the way to the store, then 15 minutes later your are 14.9 on the way home?!" But its nice to see it settle into the sweet spot when you put the pedal all the way down. Know that if you hurt your motor it wont be because of fuel mixture.
Never see EFI ratios in a carbureted engine, it just isn't possible. On the other hand, "14.7" or whatever stoich is for a given fuel is a theoretical number and not often seen either. 16 to 1 is fine cruising on flat ground in a normally aspirated engine, that's what you want.
I agree that it's great to see if your setup is safe, and kind of close. I drove with one in my 55 for a few years, I learned to laugh at the numbers, and keep driving. Then I used it to set up the "new" carbs for my Chevy II (while the blower was still on the 55), found one thing that could use a slight adjustment, and then swapped all the stuff to the Chevy II, but never put an AFR gauge on the car. Been happy with it for years now. btw I did have one carb that gave EFI numbers, although I only had the AFR gauge on it for one trip into town (that was enough to tell me I didn't need an AFR gauge). It was on a mild 454 in an old truck, and the carb was a stock Qjet, that was working right. The numbers were fantastic! that's a great carb. For a mild engine, that is.
TRUTH. I put one on my 59, drove me nuts. Didn't help me tune it, helped me make it worse. I took it back off and jetted by the seat of the pants dyno, took her to the strip and ran my best ET ever in that set up. Reading plugs and testing worked out far better for me.
I had a Holley 950 hp that would get me around 11.8 to 12.5 at light cruise. Thing was horrible and could never jet it down or tune without it affecting something else. Under full throttle it was perfect at 12.5-12.8. Great drag racing carb, not so much for the street. Ended up putting my little Quick fuel 750 back on with the light cruise numbers at 15-16 and full throttle at 12.5-13. Clean plugs and 25% better fuel mileage. This on a 512 BBF. I think there a great tuning tool but I still pull a couple plugs to make sure the readings are correct.
My little '40 hits the number just about on the money at a light cruse. My advise is dial in your cruse so it is not too fat, dial in your wide open throttle so it is not too lean, and don't worry about it other than that. -Abone.
I use one for a tuning tool on my 471 blown 406 sbc in the coupe. This engine is pretty radical for the street, more at home on the track. At cruise 14.0- 14.9ish. Hammer down 11.5- 12.5ish. That is with a modified 950 QF carb . Like was stated I do not get to hung up on the numbers. Still read plugs etc.
Modern fuel blends, especially those containing Ethanol, make it increasingly difficult to read plugs properly. You can be far-off, and still have a good looking plug.
On a positive note, most aftermarket carbs are set up to run kind of rich. So, if the carb is pretty close to being the right one for the application, it won't be lean very often, if you leave the damn jets alone.
XX2 on plug reading, just look @ newer vehicles , tail pipe black , A ""GOOD "" Quality wide band O2 is needed to tune efficient and Performance. Once you dial in ,then you can remove the gauge & 02. On some set up (carb) I have drill added a stain of wire & Etc on Radical motors Street driven ,I have a few carbs that are Completely Justable in every aspect of a function of a carburetor.
It is a universal truth that if you are over-rich, or over-lean, you are leaving power and performance on the table. Too lean, and you are headed into preignition territory. Too rich and you are literally burning money, for no viable return (don't say fun, considering better performance would pay off with MORE fun). What dyed-in-the-wool hot rodder is satisfied with that? I certainly am not. I am about to hit the decade-mark, tuning with a wide-band Oxygen sensor, or sensors. I have since added thermocouples, to observe individual cylinder performance, where possible. Beyond that, I have largely moved away from anything resembling a carburetor. You can get them close, but never exact. For exact, a computer is required, but we cannot talk about those here.
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