I'm working on a 1983 f350. The old carb is warn out and needs replaced. I'm looking at the holley two barrels. What size do I want? Is the 350 big enough or should I go with the 500? Also what size of jets should I start with?
The truck is a ranch pickup, it doesn't pull any thing. it just feeds cows and bounces though the pastures.

 

What intake manifold are you going to use?
I don't know of a two to four barrel adapter that will cover the egr port "ear" in the stock intake.

Use the 500. 350 is going to have that big engine breathing through a cocktail straw any time it needs to climb a hill.

Decide on a manufacturer, then look at their recommendations.
If you said you wanted jetting for a Holley 600 or 750 on a stock engine there would be answers in the 'carbs by list #' tech info on their website.

 

you sure it has a 2 barrel now, I worked for Ford back then and don't remember any 460's with 2 barrels. Although drugs were involved back then so the memory may be not to good....

 

I know some '70's cars had a big two barrel, but I haven't seen a pickup truck with one.
I guess anything's possible with first year introduction.

 

I threw a 600CFM Edelbrock on my daughter's plenty of power in it

 

If I recall correctly the 460 was never fitted with a 2 BBL carb the 429 was but the 460 never was . The 460 initially was the Lincoln engine and the 429 was found in the Fords.

 

Okay, that makes sense.

The "short stroke 460" got the two barrel.

600 seems normal to me, with performance starting at 750 and going up from there.

 

Lots of 370 and 429's in F600 and bigger trucks with 2bbl's. I would not go smaller than a 500. The stock 4bbl of this era is a 600, but dont forget that the cfm rating is at a different level of vacuum between a 2bbl and 4bbl.

 

Most of those medium duty trucks I've seen have governors on them as well. (at least the chip and bucket trucks I've worked on)

 

It has a ford-holley 4bbl on it now with a manual choke I'll have to check if I need that ear. I was just planning to use an adaptor plate.

 

You need to *cover* the ear.
Or you will have hot exhaust gas erupting directly under your carburetor.

Transdapt makes a egr block-off spacer, but I don't think you can stack *another* inch under the carb and have the linkages fit up to your intended two barrel.

What's the point of a 2V carb anyhow?

 

save some fuel, and should be cheaper. you only use the extra barrels when going down the road and stand on it. this thing just farts around the ranch rarely seeing 55mph any more.

 

You do understand that an engine is really just a positive displacement pump, right?

That your truck is going to draw in 460 ci of charge -every other- revolution, no matter what.
That *any* carburetor meters fuel to air flowing through it. (somewhere around 12--16:1)

I.e. each time the wheels turn an engine is going to pump a certain amount of charge through it.
And that charge is going to be ~1/14 gasoline -by weight- in order to fully burn, no matter what.

 

Not quite accurate.
That is the theoretical air handling capacity of the engine. The actual air flow or volumetric efficiency of the engine will be quite different.

The volumetric efficiency of most low performance engines at best is about 80% at peak torque (the point of highest volumetric efficiency in any engine is peak torque). All out performance engines only achieve about 95% VE at peak torque. To get beyond that you need to fine tune the induction system in naturally aspirated engines and this will only apply to a very narrow RPM range. Forced induction will allow you exceed 100% VE.


So in 1983 a 460 had peak torque of 390 ft.-lb. of torque at 2,000 rpm

Theoretical CFM
2000 x 460 = 920,000/3456 = 266 CFM

Actual CFM at 80% VE

460 x 0.8 = 368 CUI x 2000 RPM = 736,000 CUI Per min / 3456= 212.9 CFM

Or

460 x.8 =368 CUI x 1000 = 368,000 CUI Per min, convert to Cubic feet 368,000 CUI X 0.00057870 =212.9 CFM.



If you use the VE rule for engines it will help you size carbs.

So lets look at it at peak HP

the 1983 460 made 245 horsepower at 3,800 rpm

So we will still use the VE of 80% even though VE will be lower at peak HP.
We already know the CUI at 80% efficiency is 368 CUI
So
368 x 3800 = 1,398,400 / 3456 = 404.62 CFM


Spin that motor to 6000 RPM and

368 x 6000 = 2,208,000 /3456= 638.8 CFM

Also at 6000 RPM that engine is not going to be anywhere near max VE.

 

So Ford was fairly accurate putting a 600 cfm carb in my 460 truck with a 5,800 redline.
it was a simplistic explanation.

Yeah, there are always pumping losses, and a broad powerband means VE is going to suffer somewhere in something this crude.
Race engines routinely achieve over 100% filling due to charge inertia.
High venturi velocity is good for atomization, but too small compared to runner volume is going to cause stagnation.