Air Fuel Ratio - General best target to shoot for

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Cazbah362

Cazbah362

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I installed a FiTech Go 4 600 on to my 470 - 5 speed car. It runs good, just need to provide the best tune as practical for the fuel map. I have the system managing the timing so, need to balance that out. Meaning it is locked out and computer manages the "at idle" and the curve for the "all in" which goes at 2000 to about 38* right now.

The engine is a 470 440 source kit, about 10.4, with large valve 452's, small roller cam (540 lift - can get the @50 if necessary), T2, TTI's headers and FiTech - also, I live at 5400 feet and run 100 pump gas. I like to do some spirited driving, cruising, autox, and drags (mostly cruising and spirited driving)

Question is - what AFR have you learned is the best for this scenario/setup? Yes I can go with 12.5 to 13.6 but from what I read Mopars like closer to 13.2 - what can you share from practical application, and what would you recommend?

Thanks in advance
 
Cazbah362 said:
I installed a FiTech Go 4 600 on to my 470 - 5 speed car. It runs good, just need to provide the best tune as practical for the fuel map. I have the system managing the timing so, need to balance that out. Meaning it is locked out and computer manages the "at idle" and the curve for the "all in" which goes at 2000 to about 38* right now.

The engine is a 470 440 source kit, about 10.4, with large valve 452's, small roller cam (540 lift - can get the @50 if necessary), T2, TTI's headers and FiTech - also, I live at 5400 feet and run 100 pump gas. I like to do some spirited driving, cruising, autox, and drags (mostly cruising and spirited driving)

Question is - what AFR have you learned is the best for this scenario/setup? Yes I can go with 12.5 to 13.6 but from what I read Mopars like closer to 13.2 - what can you share from practical application, and what would you recommend?

Thanks in advance
Click to expand...

Mine is a small block but I run it in the low to mid 15's at idle and light cruise, and in the mid 13's when into the secondaries under load with a grand total with everything including vac advance in at light throttle (2,500-3,000) RPMs is 52 degrees advance.
The thing is, you can adjust for the numbers like you posted but it's going to vary a bit while running anyway.
This probably doesn't help you much overall, but that is what I run.
I get 25+mpg at 80 mph with the overdrive and 350-400hp

Outside of the general AFR numbers I posted, yours would probably serve best tuned on a dyno if you want to get it at it's very best in all conditions.
 
What's your cranking compression or your true compression ratio, and the advertised numbers on that cam.
This has not much to do with the AFRs, but everything to do with your timing. And you cannot really dial in the AFR until the timing is really close to optimum. They go hand in hand. and require a lot of jumping back and forth.
I think you probably know this, but
your power timing is one number and is usually not maximized until the engine can take it at full-load-WOT,without detonating.Your idle timing is another,And the rate of advance between these two is a third part of the system. The rate of advance is also usually set at WOT, to prevent detonation.
This, so far, means that only two aspects of the "mechanical" advance have been addressed; namely, the idle timing and the full load timing between idle and about 3600rpm.
As you know, the engine rarely operates at that particular setting. There are hundreds of other variables, maybe thousands.
This is where the "vacuum advance system" comes in. In your case this is the job of the MAP sensor, to tell the timing computer how hard the engine is working, and adjust the timing accordingly. There may be NON-WOT situations where the engine might like your 38* and others where it will want TrailBeasts 52* and still others where it might want closer to 60*.
As you program your timing you can begin to lean the AFR. As the timing gets closer and closer to optimum, the AFRs can continue to be adjusted, until one day you call it close enough.
Of course along the way other fuel-issues will pop up, like hesitations and bogs, and these will have to be dealt with as they occur.
The nice thing about computer controlled timing is you can run any idle timing you want to, and then pull it out as soon as the engine comes off idle; which means you can put it in gear and apply as much throttle as you want to, and never hear the dreaded death-rattle of detonation. That's my favorite thing about computer controlled timing.Well maybe the second most favorite thing.

My very favorite thing is; you can pull timing out as the rpm falls below the base idle speed. This is very handy with a stick car, cuz as the rpm falls below idle, with a big cam,the car tends to become jumpy. By retarding the timing the pressure pulses become weaker and weaker and the jumpyness moves down to a lower rpm. Until the engine no longer has enough power to pull the weight of the car,and then it stalls. With your 5-speed, you can run a pretty good starter gear, like 11 or 12. Between that and a 550 rpm say, you can parade that big engine down at 4mph, perhaps even less. That is almost unheard of with a stick car......... My kids had so much fun:) Ok, me too :)
To get away with that tho, you will probably need to enrich the engine some, and the cooling system will need to be working flawlessly, cuz at 550 rpm, that mechanical fan is not moving much air.
Oh-boy, I got off-track again.....
 
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You want the AFR to be a lot higher than that most of the time. The only time you want as rich as 12.5 would be at WOT with low manifold vacuum. When you are cruising down the freeway with low throttle opening and high intake vacuum the AFR can be 15:1 or higher. It should also be in that range at idle. I'm not sure how much control you have with your EFI system but if you have the ability to control it on the fly you should cruise down the freeway and gradually lean it out until the engine is really happy. Watch the coolant temp to see if the engine is safe. You should be able to lean it out and add spark and get the engine running really crisp during cruise.
 
Trailbeast - Yes, this helps and is good conversation, thank you.

A/J - Not sure on cranking compression, would guess above 160, but a guess. Attached is the cam card, this is a hydraulic roller advanced 6*

Yes, understand the timing, and agree AF will be secondary to the timing. Like Trail said, a dyno may be the best way for maximum but really I will probably do stop light to stop light in a rural area. As for timing, using the MSD box you can program the curve in, the Fitech does not provide that "idle" and then after 2000 all in. So with it locked out I am only going to get 38* (or what ever I program it to.) Yes, MAP is there but will need to play with it to better adjust as needed.

As for the low idle/gear, agree!!! With the carb it would jerk A LOT, I must say this is one of the cool points. Right now I am at 920 - need to work the tune in so I can lower it.

Thank you very much - please keep it coming - great conversation.

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Ah,hahahaha.
Not laughing at you, laughing at me spouting nonsense for a honking big cam as that.; 314/322/112 with 94* of overlap.
Sorry man,I have never tuned anything that big. Biggest to date was a 292/292/108 with 76 overlap.Plus I just noticed this is in the BB section, and my experience with those is very limited. I guess I'll go crawl back under my rock.
Before I go, I bet you have aluminum heads. If so; it's been my experience that they are quite happy with 4 to 6 degrees less power-timing than iron heads.
So I'm gonna sit back and try to learn something here, from you and the BB tuners. All the best to you
 
AJ - No worries, no actually have iron heads with larger valves - they are the weak link in this entire motor, but they work for now. I have a 451 with Super Victors and Indy intake setup for a fuel injection I have been working on for a coon's age - one day it will be in the car.
 
The 514 engine that I posted earlier has a 282/288 @ 050 camshaft and it will idle just fine. That is the nice thing about EFI, you can tweak the ignition and fuel parameters until the engine is happy.
 
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