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air fuel ratio question
I asked my Ford mechanic about air fuel ratio in my fuel injected Cobra motor. The custom chip is set at 12.5 to 1. My question is can I go higher with out damage to my motor? I have a street car not a race car.
He said my Town Car has 14.7 to 1 and most if not all new car / truck have 14.2 or higher. Does anyone have any experience in street tuning? What is the highest ratio I can run with out melding my motor? I think I can easily go 13.5. What do you think? Dwight |
You can easily go to 13.5-1. I run 14-1 cruising (carbureted). Under load and WOT 12 to 13-1 would be preferred.
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Cruising 14.5-14.7 no problem. WOT I shoot for 12.8-13.0
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Dwight, I think he was meaning that the WOT setting is 12.5, which is spot on. Under all other conditions, the AFR is table, based on load and rpm. Other tables add in or take away based on engine temp, maybe egr and air temp. So, there is no one afr under part throttle conditions. The ford map goes from 10 to 18, if memory serves. When decelerating the afr goes very lean.
Cruising the afr will typically target 14.7 and let the O2 trim it. |
I'm going to buy a new ECM for my GT 40 / Eight Stack system. Before I buy I want to know if the system is tuneable from idle to WOT. Thanks this information is very helpful.
Dwight |
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Dwight:
Good link to the AFR table. Stoich for regular gas for engines in general about 14.6. Stoich for the alcohol added for today's common gas mix is about 14.2 if you want to get nit picky. X2 for the 12.5 for WOT for best power output at WOT. Since most of our engines don't have knock sensors in them to warn the ECM of impending over lean conditions I'd say stay with the 14.6 max for normal operation range. You could probably get away with slightly higher if you wanted to extend your fuel mileage but you're talking sub 10% differences and it's probably not worth the effort. DonC |
Tuning capabilities
This is with regards to your question about how tunable the efi system is. It all depends what system you get, what PCM and what type of program. But if you get a standard A9l with a tweecer/QH or be you can control evrithing you want and more. Afr spark injector timing desired rpm and On and on. What afr is ideal depends on the state the engine is in, idle pat throtle or wot. It can range from 12 to past 14.5 and leaner.
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Quote:
Reason I ask is I'm adjusting my carb after I went to the dyno recently, and the dyno guy told me he usually gets the most power out of a carbed V8 engine at 10.5 to 11. He seemed knowledgeable and did some pretty radical builds in the past. Simon |
I agree with Hotfingers, 12.8 up to 13.0. 13.2 if you dare.
Your friend is losing power tuning N/A carbs at 10.5:1. |
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