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lhmurphy 02-09-2013 11:11 PM

Air/Fuel Ratios
 
What are some of your air/fuel ratios for idle in park, in gear, cruise, and wide open throttle? Just list some of your examples or experiences with your ratios! Thanks!

F-BIRD'88 02-10-2013 01:36 AM

You do not need to target a afr when ideling. The priority is idle quality.
the engine will idle best with a AFR that is slightly richer than 14.7:1
what ever give the best idle quality. Use a manifold vacuum gauge to set the idle .
off idle low cruise 14.7:1 +/-

Cruise at part throttle 14.7:1 +/-.... a bit leaner saves a bit on fuel over distance.
The limit is leanest cylinder misfire and heat. Lean needs more timing (vac adv)
don;t get all carried away. 15.7:1 +/-

Primarily on the primary main jets.

As you step into the throttle further and power the AFR should progressively shift richer.

The power valve opening point sets the transition point from cruise to power mode.

WOT Power 13.8 to 12.5:1 Being on the rich end of this helps keep things cool @ WOT
Supercharged WOT power is often tuned richer than this to avoid detonation/ and priignition . 10.5:1 to 12.5:1 as required.
There is a limit to have far this will get you. afer than, more is not better. its worse.

A afr gauge only reads the average of the cylinders. They are not all the same.
You are always tuning for the worst cylinder. A afr gauge does not read the actual AFR. it reads oxygen in the exhaust.
The AFR is a assumption based on this amount of oxygen sensed in the exhaust. Not always accurate.
exhaust leaks and ignition misfire make the gauge leaner.

lhmurphy 02-10-2013 02:48 AM

I'm liking your numbers...my engine idles between 13.5 and 14, when I start moving a little I get around 13 steady and as I get on it I hit 12 and it stays at 12 all the way until its time to slow down lol I plan on moving my secondary jets down from 76 to 73 and see how that feels...thanks for your help! I have a solid exhaust system that has no leaks that I can find...I just installed the AEM WB just bc I was curious...motor runs great but I just wish I had air bleed adjustments...I'm running a Holley 670 SA and I'm half tempted to switch to a 4150 HP for the air bleed adjustments

cdminter59 02-10-2013 09:44 AM

Air/Fuel Ratios
 
Ihmurphy, how's the 406 running? If I remember correctly you bought the 406 rotating assemby from Skip White. You had a bunch of post about your compression ratio. With your Blue Print heads your SCR was around 10.3. Does it operate good on 91 octane gas? Anyway back to your carburetor, I assumed you were using a 4150 750 cfm. I got this wesite for you to check out. SMI CarburetorSMI- Sean Murphy Induction. He will build you a custom carburetor to your engine specs.

vinniekq2 02-10-2013 09:47 AM

air bleeds are important

my air fuel ratio is set at 12:1 for w o t
13:1 for 1/2 throttle,,,depends on the power you are looking,and purpose
of your car.Go leaner for a daily driver

ap72 02-10-2013 09:58 AM

my idle is at about 12.5-13:1, cruise is at about 15.2-15.5:1 WOT is at about 12.7-13:1

if you adjust your jets down to get a good cruise AFR and your WOT goes too lean you need to enlarge your powervalve restrictors. To get a good baseline for tuning your air bleeds and emulsion circut you'll need to be able to get some good data logging. Also, your accel pump shot can be adjusted with squirters and cams, this is one of the last steps though.

BTW, once the weather changes 15 degrees you'll get to do it all over again! Aren't carbs fun? :mwink:

lhmurphy 02-10-2013 11:32 AM

Quote:

Originally Posted by cdminter59 (Post 1644736)
Ihmurphy, how's the 406 running? If I remember correctly you bought the 406 rotating assemby from Skip White. You had a bunch of post about your compression ratio. With your Blue Print heads your SCR was around 10.3. Does it operate good on 91 octane gas? Anyway back to your carburetor, I assumed you were using a 4150 750 cfm. I got this wesite for you to check out. SMI CarburetorSMI- Sean Murphy Induction. He will build you a custom carburetor to your engine specs.

It runs really good! I usually run 93 octane but had a tank of 89 at one point and it stayed running good and detonation free lol but my ? Is that I have an automatic and I plan on getting a looser converter just to help my cause but would a 4150 HP be ok for an automatic? I assume it's that way to go bc it's a light jeep with 3.73 gears and I like the idea of air bleed adjustments

lhmurphy 02-10-2013 11:33 AM

HOLLEY 4150 HP TIME? lol

lhmurphy 02-10-2013 11:34 AM

Quote:

Originally Posted by ap72 (Post 1644741)
my idle is at about 12.5-13:1, cruise is at about 15.2-15.5:1 WOT is at about 12.7-13:1

if you adjust your jets down to get a good cruise AFR and your WOT goes too lean you need to enlarge your powervalve restrictors. To get a good baseline for tuning your air bleeds and emulsion circut you'll need to be able to get some good data logging. Also, your accel pump shot can be adjusted with squirters and cams, this is one of the last steps though.

BTW, once the weather changes 15 degrees you'll get to do it all over again! Aren't carbs fun? :mwink:

Just a blast lol what do u think of the 4150 HP? I just want it bc it seems a lot more tuneable to me with the screw in air bleeds and I think my motor could benefit from the 750 cfm instead of the 670

vinniekq2 02-10-2013 12:11 PM

the 750 is a great ,hoice
If you buy from someone like Pat from the carb shop,
it will be 90% tuned for your engine,out of the box
be prepared to answer questions about specs

lhmurphy 02-10-2013 12:22 PM

Quote:

Originally Posted by vinniekq2 (Post 1644812)
the 750 is a great ,hoice
If you buy from someone like Pat from the carb shop,
it will be 90% tuned for your engine,out of the box
be prepared to answer questions about specs

Ok I'm gonna do it! How do I get ahold of Pat at the carb shop? Some contact info would be great! Thanks in advane

F-BIRD'88 02-10-2013 01:24 PM

You can upgrade your carb using the Proform 750 HP body kit.
It will require some air bleed tuning, when working with a 670 as a donor.
Re: air bleed tuning The installed air cleaner has a effect. Tune with the air cleaner on.
Not all air cleaners are created equal.

vinniekq2 02-10-2013 01:52 PM

posting from my phone,pm me,I will give contact info when I get a new pc monitor

lhmurphy 02-10-2013 02:02 PM

Quote:

Originally Posted by F-BIRD'88 (Post 1644851)
You can upgrade your carb using the Proform 750 HP body kit.
It will require some air bleed tuning, when working with a 670 as a donor.
Re: air bleed tuning The installed air cleaner has a effect. Tune with the air cleaner on.
Not all air cleaners are created equal.

I had read somewhere about this change but I think I'm gonna keep the 670 SA in storage after I clean it up, and have a back up carb that I know is in good working order


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