Fuel Air Ratio
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Instructor
Joined: Jun 2019
Posts: 232
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Fuel Air Ratio
My '81 has a freshly rebuilt 350 with an AVS2 Carb, HEI Dist and headers. I'm wondering if I put fuel air/ O2 sensors in the headers, would it help with the carb tuning? I'm thinking if I put a sensor on each side, leading to a gauge, that it would help get that 14.7:1 ratio.
Yes I know,,, and I've been told all my life,,, I think too much and I'm ****. Guilty! 🤔
Yes I know,,, and I've been told all my life,,, I think too much and I'm ****. Guilty! 🤔
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
There's no point in running an O2 on both sides - you'll never balance out the two sides perfectly with a carb, so don't attempt it - just put a bung on one side. Even better - Forget the bung and just put a probe up the tailpipe for use during tuning and then remove it.
If you're running pump gas, which has 10% ethanol in most parts of the country, you don't want to hit 14.7 at idle or cruise. You need to richen it to the low 14's at idle and light-throttle cruise, and around 12 - to low 12's at WOT.
Lars
If you're running pump gas, which has 10% ethanol in most parts of the country, you don't want to hit 14.7 at idle or cruise. You need to richen it to the low 14's at idle and light-throttle cruise, and around 12 - to low 12's at WOT.
Lars
Race Director
Joined: Jan 2000
Posts: 12,399
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From: San Jose CA
These gauges are pretty dumb, and will scale by a constant from lambda. I've actually conversed with the people who built my wideband setup (FAST) and they use a simple scaler.
If a car is running at stoich for E0, E10 or E85 the gauge will show 14.7 even though the actual quantity of fuel and air is vastly different depending on the blend. Some may allow you to change the scale, of course.
I actually chased my tail for a while trying to tune my very first VE table, shooting for E10 stoich, using that as the target AFR and pumping it into error calculations to correct the cells. When I switched to lambda math for calculating error I had the VE table tuned in a couple quick drives (minus WOT).
I am running a 15.0 target for cruise, low 14s for idle and mid 12s for WOT on my SBC400. The higher cruise helps with emissions which is one challenge unique to me in CA.
Last edited by Shark Racer; Jan 3, 2020 at 09:57 PM.
Le Mans Master
Joined: Dec 2006
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Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
