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Discussion Starter #1
My air fuel ratio is too rich, I think 13 to 1 is the optimum.
The question, is this something I can fix without computer programming.
See dyno sheet in sig.
 

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Discussion Starter #3

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A/F Ratio Comments

FRC Tom said:


pmontelo:
Thank you for the links it seems that 11.5 to 1 is the best torque at WOT and 12.5 to 1 is the best power at WOT.
The question now is do I want more power or torque at 6500 rpms?
Hummm :confused: :roll:. If you change the torque at 6500 RPMs by say 3%, you also change the HP by 3% since they are directly related by the equation HP = (T x RPM)/5252. Torque and HP are directly related at any given RPM.

Yes, you will have to reprogram the ECU to change the A/F over the RPM range.

11 to 1 is alittle too rich. 12.5 to 13.0 is OK for a non-turbocharged engine. Turbos are run alittle richer to help prevent detonation. Rotary turbos are even richer at WOT.

Obviously you had the A/F measured during a dyno run, and most dynos use a wide-band O2 sensor (menaing it's output is alot more sensitive) -- it has a wider output 'band' -- then the O2 sensors installed in the Vette's exhaust pipes. When ever possible, always use a wide band instrument for A/F tuning.
 

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Power enrichment here

Hi there,
Sorry I am late, but here is where it starts. Remember that at wide open throttle, you are under power enrichment, you will NEVER, nor should you ever be at 14.7 to 1 which is ideal.
Under power enrichment, you are adding extra fuel to prohibit detonation, this is a result of the calibration of the PCM.
Now, if you were experiencing other issues, like the detonation or whatever, you could have an issue, but on a dyno run, when you are at WOT, this should be considered normal.
I would consider you normal.
Just a side note, the 14 is the air side, and 1 is the fuel side, so you need 14.7 parts of air to 1 part fuel, correctly mixed, to create ideal combustion.
Best to you, so your spec of 13 parts to 1 part is actually rich, I will be on Thursday, so let me know what you have, c4c5
 

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Discussion Starter #6 (Edited)
Thank you c4c5:
I was concerned because the other C5s that were dynoed that day all had a stable AFR (straight line) across the entire rpm range and mine starts dipping (getting richer) at about 4000 rpms.
Would this be the difference from a stock computer to my reprogrammed one?
 

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FRC Tom said:
Thank you c4c5:
I was concerned because the other C5s that were dynoed that day all had a stable AFR (straight line) across the entire rpm range and mine starts dipping (getting richer) at about 4000 rpms.
Would this be the difference from a stock computer to my reprogrammed one?
If you sent your computer out for reprogramming, then I'd say "yes". that's why it's richer at higher RPMs.

I assume they reprogrammed it based on your exact mods? Please re-read my earlier post above to your question :D.

IMO, you should be able to get alittle more high end HP if the A/F was in the 12.5~13 range. So what A/F where the other Vettes with flat A/F ratio lines running?
 

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Hi there,
I would agree, that your pcm reprogram is most likely the issue here.
It is not uncommon, nor should it be deemed a bad thing.
Best toyou, c4c5
 

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It would have been nice to see the A/F mixture on the stock computer calibration.

I agree the computer re-calibration might be the reason for the slightly rich mixture. Depending on your mods, they may have richened it up for power and/or safety.

At 6500 RPM, your concerned most about making power.

I would think that around 12.5:1 would be ideal at WOT, running with 93 octane fuel on an LS6. You might be able to run it leaner, but I would look at using a lower temperature thermostat if you do. Still, I doubt you'll do better at WOT going leaner.

Keep in mind that the Z06 engines naturally run fairly hot and with a decent amount of compression, 10.5:1. If you got a fairly high compression engine that runs hot, and you want it to run with low octange gas (which you can on the Z06), the last thing you want is a lean A/F mixture.
 
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