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Old 01-06-2013, 09:15 PM
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Air Fuel Ratio Gauge

Is it worth tuning a carb with an air fuel ratio gauge? I have headers with the O2 bungs welded in. I was thinking about buying the O2 sensors and an AFR gauge. However, my cam, in a sbc 350, has a lot of overlap 227 @50 .565 lift on a 108 LSA. It is my understanding that a fair amount of unburnt fuel is pulled into the exhaust valve and passes out the exhaust. With more overlap can you get an accurate reading on an air fuel meter or gauge? My concern is it will read rich when it is not. Other option is simply read the plugs and be done with it. Thanks for the help.

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Old 01-07-2013, 03:21 AM
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An air fuel gauge doesn't care about cam, head or carburetor choices. It is reading the ratio of air to fuel mix. It would be a great tool for you in terms of tuning your engine.
Like you mentioned, when the car idles you can smell gas. That is not because of your cam, but rather it is because your idle circuit is too rich.

How do you currently tell rich or lean when cruising or WOT?
There are many ways to tune that are tried and true and they don't require an AFR gauge. But once you put one in, you'll wonder how you got by without it - NO MORE GUESSING.

Recommend Innovate as a quality product. Oh, and of course a wide band. Do not bother with a narrow band for unless your only concern is emissions.

Good luck.
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Old 01-07-2013, 03:34 AM
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I instaaled AFR long time ago. I have to keep replacing the o2 snesor. I use race fuel 110 octane seems the lead keeps clogging up the o2 sensors. Any suggestions? Also I love how easy it became to tune my car. it was wort 2 tenths in the 1/4 mile.
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Old 01-07-2013, 06:32 AM
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Quote:
Originally Posted by cadillacdave1 View Post
Is it worth tuning a carb with an air fuel ratio gauge? I have headers with the O2 bungs welded in. I was thinking about buying the O2 sensors and an AFR gauge. However, my cam, in a sbc 350, has a lot of overlap 227 @50 .565 lift on a 108 LSA. It is my understanding that a fair amount of unburnt fuel is pulled into the exhaust valve and passes out the exhaust. With more overlap can you get an accurate reading on an air fuel meter or gauge? My concern is it will read rich when it is not. Other option is simply read the plugs and be done with it. Thanks for the help.
Might not help in all areas of the rpm band but wil show if its going lean int he top end or under wot. Basicly you got to think rich is good it should always show rich or just close to rich to be safe tune then lean it out a little at a time to se if you can make some more power without going lean.

They work well. Also looks cool to have another guage move when you hit the gas.
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Old 01-07-2013, 12:12 PM
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Trying to tune today's motors without an AFR gage is very difficult. It's not the end all of end alls but it sure helps.

You also need a very good understanding of your specific carb or EFI. There are a number very good books that will point you in the right direction.

Be aware that some carbs are going to have to have some adjustments installed that are not there to begin with......air bleeds and idle feed restrictions. You will need to be very careful doing this as there usually is not a lot of material and some of the carb parts are quite brittle. You can trash a carb if you are ham handed. Get the right tools.

There is a wealth of aftermarket parts that will help in the tuning but again you need the basic knowledge to start.
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Old 01-07-2013, 03:00 PM
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Thanks 4 the response. Actually I don't smell gas at idle. My concern is that with the large overlap cam, unburnt fuel is discharged into the exhaust, thereby not giving an accurate reading on an AFR gauge, since the gauge may be reading this unburnt fuel as rich, when actually a cam like that runs that way. II don't want to waste the money on sensors and a gauge if it won't help with this cam. The car runs very well and I have tuned according to the plugs, but feel that a gauge may be more accurate than simply reading plugs.
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Old 01-07-2013, 03:07 PM
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The air-fuel ratio gauge read oxygen content in the exhaust, not the amount of fuel in the exhaust. They wont work well at idle but for cruise an WOT they can be a benefit if you really want to tune to maximum lean driveability.
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Old 01-07-2013, 06:15 PM
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The Innovate gage works quite well at idle. It is very fast reading and accurate.

One thing that is a must is to wait for the O-2 sensor to warm up before you start the motor. Just like a diesel with it's "wait to start" light. If you don't and the fuel vapors hit it, it will eventually burn out. Already lost 2 this way. They cost $55 at the auto parts store.

I'm sure someone will say "My fine GM car starts and runs just great without waiting" however it has an EFI which will have excellent control over the AFR at all times so you won't be washing fuel into the ex like a carb does.

If you think your NA motor throws raw fuel into the ex, try a 6-71 blown motor with 2 750 DP on a cold start up say 10 deg or so.

Also as I've said before here, it takes a good 1/2 hour running to get the motor up to even operating temp before you will get accurate readings on the AFR. You can clearly see this as the gage changes and settles down as the motor gets warm. Just because you get heat out of the heater in 2 minutes does not mean the motor is thoroughly warmed up.
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