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Discussion Starter #1
Have a quick question. If you had a very lean condition running alcohol would it burn the strap off a plug or have a popping out the exhaust before and engine damage. Reason I ask is My o2 sensors are installed in the collector. The car will repeat numbers in the 1/8 & in the 1/4 mile. I am picking up less than 10 degrees of water temp in a 1/4 mile run. I have no engine popping, plug straps look good & the engine is pulling hard all the way through but..... my o2 readings in the 1/4 mile are 6.5 or higher. I have a front mounted fuel cell with a Magnafuel Prostar 500 pump. 12 to 10 to 8 lines to carb. Apd 1050 Carb. I just think maybe I am getting false readings
 

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If you're picking up less than 10 degrees water temp (with fan off) in 1/4 I'd think you were on the fat side ...... I agree with the false readings .
 

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Find someone that knows how to read alcohol plugs. Is the top ring discolored all the way around down to the first thread? Is there a color change near the bend of the ground strap? Are you using NGK plugs so you can read them easier? Heat range? Timing?
 

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I would do a free air calibration on your O2 and make another pass before changing anything. I would also think it would lay over on a 1/4 pass is it was that lean. Are both sides reading 6.5?
 

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Discussion Starter #9
I am using Autolite Ar3911. Timing is 34 degrees. This is a BBC 540 with Brodix BB2xtra Heads. The Timing mark on the ground strap looks to be around the center of the bend. These plugs have 100 runs on them so they need to be changed anyway.


Find someone that knows how to read alcohol plugs. Is the top ring discolored all the way around down to the first thread? Is there a color change near the bend of the ground strap? Are you using NGK plugs so you can read them easier? Heat range? Timing?
 

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Discussion Starter #10
I will take a pic of my racepak graph with the o2's on & post it.


I would do a free air calibration on your O2 and make another pass before changing anything. I would also think it would lay over on a 1/4 pass is it was that lean. Are both sides reading 6.5?
 

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Discussion Starter #12
You can see my o2 readings are all over the place. A friend of mine has o2 sensors in his collectors and his readings look a lot more stable.
 

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How far away from the end of the collector are your sensors? I don't use Racepak, but maybe you need to smooth the graph. Here is one of mine, but it is in the individual pipe and I have it smoothed with a filter in the software. I am rich on this pass, the weather was horrible that day. Yours does look somewhat lean by the graph, but different engines like different O2 readings.

 

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Discussion Starter #14
They are right in the choke point of the merge collector. Your graph looks pretty stable across the run for you o2
 

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Get a few sets of NGK plugs and change them after 1 pass. R5671A-9 possibly. You can read them easier. Even better if you cut power and coast to the return road and have someone tow you back to pits and change plugs before next pass. If you have any truck pull friends that are on alcohol, they may be able to read them well.
 

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Discussion Starter #16
Ok. I have a new set of NGK R5672A-8. I think that is equivalent to my AR3911 plug. Is the R5671-9 a colder plug
 

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Nothing wrong with their placement. A few options. Jet up until you stop gaining MPH or it starts to pop, talk to someone about your recorder / graph roughness, race it like it is. No matter what any of the rest of us have for o2 readings yours can be different. If you are only gaining 10° or so then I wouldn't think it was too lean, but jetting up until you get a change is safe. Then you can work it back down.

What kind of et and mph do you run? Just curious.

Curtis
 
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