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 1Likes
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1
Post By Hotfingrs
03-02-2014, 02:04 PM
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Senior Club Cobra Member
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Join Date: May 2001
Location: Florence,
AL
Cobra Make, Engine: RCR GT 40 & 1966 Fairlane 390 5 speed
Posts: 4,511
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Not Ranked
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
__________________
''Life's tough.....it's even tougher if you're stupid.'' ~ John Wayne
"Happiness Is A Belt-Fed Weapon"
life's goal should be; "to be smarter than inanimate objects"
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03-02-2014, 02:25 PM
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CC Member
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Join Date: Jun 2007
Cobra Make, Engine: SPF GT40
Posts: 236
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Not Ranked
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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03-02-2014, 03:03 PM
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CC Member
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Join Date: Dec 2001
Location: Castalia,
Oh
Cobra Make, Engine: EM cobra, 450 inch sbc running a best ET of 9.14..so far..ALL MOTOR...approx 800 horse.............ERA with 482 FE..All Aluminum Engine
Posts: 1,395
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Not Ranked
Cruising 14.5-14.7 no problem. WOT I shoot for 12.8-13.0
__________________
Jack
XSSIVE .....
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03-02-2014, 06:23 PM
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CC Member
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Join Date: May 2006
Location: St. Louisville,
Oh
Cobra Make, Engine: A&C 67 427 cobra SB
Posts: 2,444
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Not Ranked
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.
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03-02-2014, 07:32 PM
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Senior Club Cobra Member
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Join Date: May 2001
Location: Florence,
AL
Cobra Make, Engine: RCR GT 40 & 1966 Fairlane 390 5 speed
Posts: 4,511
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Not Ranked
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
__________________
''Life's tough.....it's even tougher if you're stupid.'' ~ John Wayne
"Happiness Is A Belt-Fed Weapon"
life's goal should be; "to be smarter than inanimate objects"
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03-23-2014, 06:04 AM
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Senior Club Cobra Member
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Join Date: May 2001
Location: Florence,
AL
Cobra Make, Engine: RCR GT 40 & 1966 Fairlane 390 5 speed
Posts: 4,511
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Not Ranked
__________________
''Life's tough.....it's even tougher if you're stupid.'' ~ John Wayne
"Happiness Is A Belt-Fed Weapon"
life's goal should be; "to be smarter than inanimate objects"
|
03-23-2014, 06:52 AM
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Senior Club Cobra Member
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Join Date: Jun 2003
Location: West Linn,
OR
Cobra Make, Engine: ERA #684, 428 FE, TKO600
Posts: 1,378
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Not Ranked
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
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04-15-2014, 10:04 PM
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CC Member
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Join Date: Nov 2013
Cobra Make, Engine:
Posts: 2
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Not Ranked
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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04-16-2014, 08:52 AM
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CC Member
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Join Date: Jan 2004
Location: Shawbury,
Posts: 325
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Quote:
Originally Posted by Hotfingrs
Cruising 14.5-14.7 no problem. WOT I shoot for 12.8-13.0
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Hotfingrs, are these actual WOT numbers from your 800hp engine?
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
Last edited by CobraV8; 04-11-2024 at 05:31 AM..
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04-16-2014, 12:52 PM
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CC Member
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Join Date: May 2008
Location: Brisbane,
QLD
Cobra Make, Engine:
Posts: 2,773
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Not Ranked
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.
__________________
Gary
Gold Certified Holden Technician
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