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Discussion Starter #1
I’m installing an o2 system in my car. The system will output 12 volts upon a user selected AFR. I’m going to use this signal to retard timing should my motor run into a lien condition. What AFR would you select and how much timing would you pull?
It’s a SB Ford, 15:1, carbureted, normally runs 34 degrees of timing.
 

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Are you going to have dual O2's or just hoping it will read a lean condition on one side of the engine? It is set up to pull timing only at WOT or at all times?
 

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Discussion Starter #3
Are you going to have dual O2's or just hoping it will read a lean condition on one side of the engine? It is set up to pull timing only at WOT or at all times?
One o2 for now. It will pull timing once the triggering event happens. The system will not turn on until the pre-selected rpm is met. I was thinking 5,000 rpm. Thoughts?
 

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Discussion Starter #4
Can someone help me please? I’m installing the system this weekend and going racing next weekend. I don’t want to do more harm than good. I was thinking of setting the O2 system to trigger a timing retard at an AFR of 13.5. Is that too low or too high? I also have no idea how much to retard the timing or if this is a good idea in the first place. I have an MSD AL3 so I can choose to retard timing between 1 to 20 degrees.
 

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Was the engine dynoed? I never had a reason to have to do this in the first place and go through the effort and spend the money. If it wasn't dynoed and you are using track performance to tune it, start low on the timing and creep up on it with each pass. Hvaeing an o2 is not a bad idea, as you can use it to get a reading as you tune it. When power starts to fall off after timing and jetting is set, you will have a number that reflects peak power. 13.5 is not that lean. If you creep up on the tune up and read plugs, you won;t have a problem. I wouldn't base too much on the number though, look more at the actual performance from your mph while tuning.
 

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Discussion Starter #6
Was the engine dynoed? I never had a reason to have to do this in the first place and go through the effort and spend the money. If it wasn't dynoed and you are using track performance to tune it, start low on the timing and creep up on it with each pass. Hvaeing an o2 is not a bad idea, as you can use it to get a reading as you tune it. When power starts to fall off after timing and jetting is set, you will have a number that reflects peak power. 13.5 is not that lean. If you creep up on the tune up and read plugs, you won;t have a problem. I wouldn't base too much on the number though, look more at the actual performance from your mph while tuning.
Thank you Kris. The engine was dynoed, both on the engine dyno and chassis dyno. But I just had a new carb built. I plan on tuning with the plugs and AFR. It’s the first pull that concerns me. In the past (not this car) I’ve had several cars chassis dynoed and have seen tuners abandon a run if they see an AFR they don’t like. So I hate to roll the dice on my first pull with the new carb. I have already bought the system so what’s a good starting point? Maybe set AFR 14 – pull 5 degrees if it hits that lien?
 

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Discussion Starter #8
ALTRONICS??? i have one of those to. ran mine all year long at 13.8 - 14 on q-16 had no problems. I couldnt get it any richer. Just ordered new metering blocks.
Yes Altronics. Thanks for your reply.

Was this a dumb question? No one answered my question. What AFR and how much timing to pull?
 

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Just run the thing down the track and adjust accordingly.
Your not going to hurt anything on one pass.
If you start knocking timing out of it you will have useless data for the next pass.
 

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I would dyno it and watch the BSFC #, as well as the o2 and tune for max power and see what the o2 says at max power. Then set it for a couple numbers higher as a precaution. The o2 number can be misleading, as I have had engines run 15.5 on the hit and thought the dam thing was gonna melt down, but it lost power richening it up to lower them...Type of fuel used will play a big role in the number as well. Fuels designed to run on spray like c16 will drastically lower them when running n/a. Like I said, run the right fuel and start with timing set real low. Make your pulls and creep up on it. You won't hurt anything. Just keep looking at plugs after each pull. You will see it if anhything starts going bad...before it actually goes bad. As far as a number..every engine is different. Tough call. Like it was said, high 12's to mid 13's is good. I have seen 14's run well. Just monitor everything else. If you need a failsafe, set it for 15.1 and pull 5-10*..you won't hurt anything below 15.1.
 

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If you are using it as just a safety backup then yes I'd probably set it to pull ~5 degrees at 14.5 and have it kick a light on the dash.
 
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