AFR Numbers. Teach me... - Vintage Mustang Forums
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post #1 of 19 (permalink) Old 07-13-2019, 12:32 PM Thread Starter
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AFR Numbers. Teach me...

Since I installed the FiTech. I have been playing with tuning it. What are some good AFR Numbers to try and hit?

...Marco

'65 Mustang Inline 200. CI Aliminum Head, Holley 350,
Schneider 264/274 cam, Headers, Recurved DSII, MSD 6A, and a whole lotta other stuff!
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post #2 of 19 (permalink) Old 07-13-2019, 03:37 PM
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Typically 14.7. You will never hit it solid though. Best to tune it for how you intend to drive it.

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Patrick
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post #3 of 19 (permalink) Old 07-13-2019, 03:49 PM
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It depends how radical your engine is but 14 is generally good for idle and off idle, mid to high 13's for light cruse, 12's for heavier throttle to wide open. These are just starting points that usually work and that you can tune off of. This would be for gas also and natural aspirated engines. If you can run that thing in learning mode then look at the tables it comes up with for A/FR what is it doing?
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post #4 of 19 (permalink) Old 07-13-2019, 04:10 PM
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What are the rest of the engine specs? Different combos will tolerate different stuff. I lean the idle out until it has a hard time keeping the afr steady then richen it up til itís steady, on my other make itís about 14.2. Cruise is 14.5, and I do the same thing, put it in the afr adjustment setting, drive at your cruise rpm and lean it out until it kinda surges then richen it up so itís steady. Full throttle I just set it at 12.7. Keep in mind changing the idle and cruise might also require a change in the accelerator setting. It took me a while to get it set but I havenít messed with mine in a couple years now. There is also a good Facebook group fir questions and answers.

69 Mach One, 428CJ, 5 Speed, 3.91's.
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post #5 of 19 (permalink) Old 07-13-2019, 04:12 PM
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my sniper is tuned to 14 idle, 14.6 cruise, and 13 WOT --- seems fine. its it the perfect settings for my engine? no idea - i've been meaning to go to a dyno and have them figure that out

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post #6 of 19 (permalink) Old 07-13-2019, 04:15 PM
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Well, 14.7 may be stoichiometrically "perfect" for combustion, but not for "real world" operation. I think GregB's suggestion is pretty good...you can go from there depending on performance and plug reads....

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post #7 of 19 (permalink) Old 07-13-2019, 05:33 PM
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Theoretically, 14.7:1 is stoichiometric perfection or whatever for idle.

In practice, it's going to be whatever your cam wants it to be. Jane does best at 13.8-14.0 AFR, for example. General rule of thumb is to put the AFR where your car idles best - my criteria are that the car idles smoothly and doesn't smell very strongly of exhaust/gas.

Usually people put 12.5 AFR for WOT, and cruising is usually 14.0-14.2. You'll have to play with it and see what your car likes though, again.
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post #8 of 19 (permalink) Old 07-13-2019, 06:14 PM
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In reality if you have 14.5-14.7 at cruise, the car will often stumble under any throttle input. I am happy to hit 14.2 at cruise. Most of my cars idle happily at 13.8...and WOT is anywhere from 11.5-13.2 depending on whether it's a boosted car or not, how much boost I am running at a given RPM, etc.

That being said, I have succesfully been able to cruise on some setups as high as 15.1
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post #9 of 19 (permalink) Old 07-13-2019, 06:20 PM
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Quote:
Originally Posted by patrickstapler View Post
Typically 14.7.
Quote:
Originally Posted by Woodchuck View Post
Well, 14.7 may be stoichiometrically "perfect" for combustion, but not for "real world" operation.
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Theoretically, 14.7:1 is stoichiometric perfection or whatever for idle.
C'mon Patrick, even we Alabamians know that 14.7 is stio...stoik...stoicio...uhmm, just right in the lab but not on the street...

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post #10 of 19 (permalink) Old 07-13-2019, 07:44 PM
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I caveatíd...twice. You will never achieve it and tune the car to how you drive it. I recently had to change mine from cruise tune to WOT tune. Hard to set up a engine for opposing ends of the spectrum...especially with a naturally aspirated carbíed engine.
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post #11 of 19 (permalink) Old 07-13-2019, 09:05 PM Thread Starter
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Thanks for all the info everyone! This gives me a good start.

I am also considering taking a EFI Intro course for some more basics from EFI University. https://www.efi101.com/modules/

...Marco

'65 Mustang Inline 200. CI Aliminum Head, Holley 350,
Schneider 264/274 cam, Headers, Recurved DSII, MSD 6A, and a whole lotta other stuff!
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post #12 of 19 (permalink) Old 07-13-2019, 09:15 PM
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Quote:
Originally Posted by 65coupei6_2 View Post
Thanks for all the info everyone! This gives me a good start.

I am also considering taking a EFI Intro course for some more basics from EFI University. https://www.efi101.com/modules/
If you are going EFI...consider Megasquirt...the units are dirt cheap if you assemble yourself with even the top-of-the-line pre-assembled units costing $1200. For a pushrod v8 you could get away with a $250 unit though...use with a TBI if you want the carb look, or with any number of EFI manifolds for something that will be closer to ideal...cant beat the price for a full standalone system that can do whatever you want...and has plenty of forum support. I have built 3 or systems over the years and couldn't be happier...even hooked up traction control 2 times(one of the many options) and am currently using one to control a VGT turbocharger.
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post #13 of 19 (permalink) Old 07-13-2019, 10:24 PM Thread Starter
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Figured I would post my engine specs. in case anyone has some more insight.

65/200 cubic inch block bored over .060
Vintage Inlines(CI) Aluminum Head 52cc chambers
9.6:1 Compression
Squared the deck. 17-10 thousandths
HSC 2.3l Flat top pistons
Everything Balanced.
New Rods, bearings, oil pump, etc ...
1.6 adjustable rockers (1.5 was stock)
3/8 Push Rods from Smith Bros. (5/16 was stock)
Recurved DSii /MSD 6A. Thanks Bill !!
Schneider 264-74H cam 110 lobe
Clifford single out headers/Black Window Venom muffler single in-dual out
PowerMaster Mini-starter
FiTech 30003

Currently likes to idle @ 950 rmps with low vacuum under 15 and 13.6 afr

...Marco

'65 Mustang Inline 200. CI Aliminum Head, Holley 350,
Schneider 264/274 cam, Headers, Recurved DSII, MSD 6A, and a whole lotta other stuff!

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post #14 of 19 (permalink) Old 07-13-2019, 11:18 PM
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Sounds about what you can expect from the bigger cam.
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post #15 of 19 (permalink) Old 07-14-2019, 01:51 AM
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What's your initial timing? I don't think that cam is all that big, I'd wager with a little tuning it would idle about 800, maybe a little less. Have you set the throttle blades so the IAC is between 3 and 10 at idle?

69 Mach One, 428CJ, 5 Speed, 3.91's.
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