[Tom Vaught]

One more simple calculation, for you, that tells you airflow numbers and how many cubic feet of air mass you would have if you were at sea level and in 70 degree air temp if the carb were flowing 1 pound of air mass in one minute.

Here is the formula:

"A Constant" times Ambient Pressure (Units is Inches of Mercury)

So for example that would be the constant:
1.3562 times 29.921 Inches of Mercury

(29.921 is considered to be the standard pressure at Sea Level conditions)

You come up with 39.66387602

On the bottom of the calculation you have:

A constant (459.67) plus the local Temperature
in degrees F. (We will use 70 degrees Fahrenheit) So 459.67 Plus 70 degrees is 529.67

So then we divide 39.66387602 by 529.67 and we get: 0.074884 pounds per cubic foot of air mass.

If we divide 1 by 0.074884 pounds per cubic foot of air mass we get 13.35398 cubic feet of air mass in that one pound of air at those conditions.

The reality is a typical engine flows between 17 and 19 cfm at idle so slightly more than 1 pound of air mass at idle is going into the engine each minute.

Hope I made the math easy for you to use in the future. Once you get that part of the air equation you can relate it to the fuel calculation in pounds per minute for a given air/fuel ratio.

Tom V.

[Tom Vaught]

Here are a couple of simple to use calculators for estimating Holley carb cfm for the engine horsepower you want:

https://www.gregraven.org/hotwater/c...ors/airflow-hp


http://www.1728.org/mtrair.htm

Both calculators assume the following:

Air flow (CFM) = (Horsepower × 0.625) × 1.1104


Horsepower = (Air flow × 1.6) × 0.9


The assumption is that you can make 1.4409221902017300 horsepower per CFM of Air.

Works for me as a simple calculator.

So with our 13.35398 cfm of air per pound of air mass (in the previous post) we would make 19.23 horsepower for that pound of air mass going thru the engine.

Tom V.

[shaker455]

Tom,
You should compile a book with all your trade experience!

[Tom Vaught]

Nice of you to say that Jeff but Mike Urich and Chuck Gulledge pretty much have already covered everything.
They were very good Carb Mentors in the 70s.
Mike, I think, wrote 4 or 5 Holley Books over the years and Chuck Gulledge started his own carb tuning business
when he left Holley. He built a lot of very good Dominators for people. A Pair of "old" Chuck Gulledge Dominator Carbs
(with the dust blown off of them) made 30 more HP on a Pro Stock Truck vs the "other" Pro Stock Carb Guy's
"latest and greatest" $$$$ stuff.

On the same subject, Writing Books, Corky Bell, A friend from the 'Hill Country' of Texas has
some very good books on Boosting engines with either Centrifugal Superchargers or Turbochargers.

So I will pass on the 'Writing Books', Jeff.

Tom V.

[shaker455]

Well I was gonna say not limited to Carbs...

[Tom Vaught]

Thanks for the compliment anyway Jeff. Appreciated.

Tom V.

[Tom Vaught]

Going to post some info on how to identify different Holley Carbs today with some pics.

All Holley carbs, except for prototypes that may not have been stamped, will have a 'List Number on them. The List Number could be in various places depending on the carb but the parts will be stamped with a number and sometimes with a Ink Stamp too.

So the List Number will have a Carb Model Number and a Date Code on the carb. Most times on the air horn but in the case of Dominator Carbs it could be on the air cleaner "Ring" or possibly on the side of the mainbody.

Here are some pics as examples:

The 1st pic is a "Chevrolet" production carb and has a Chevy number as well as a Holley List Number and "Vintage" of the carb.
In this case "-1" which means that it is a very early carb in that "List Number" history.

The 2nd Pic is also a Chevy type carb with a "Chevy Part Number and list number but does not have a "Vintage" Number.
Basically the carb is calibrated with the same calibration that was offered in the 60s and 70s.

The 3rd Pic just shows the same info I have posted previously. Pic 3 covers the Square Bore 4150 type carbs and Pic 4 covers the Spread Bore carbs.

Pic 5 shows the list number stamped on a Dominator 4500 Carb (a "List Number" and Date Code".

As mentioned above a "-1" carb would be a 1st Production Run type type carb but if you had a 4150 Double Pumper with a "-6"
on the air horn you would have the first Double Pumper Carb with "4 Corner Idle" Capability. There would have been 4 other changes
to the carb, after the "-1" carb before the "-6" was released.

So this "identifier" helps a lot in swap meets with the "age" of the carb.
Typically the base of the Throttle Body will be stamped with the List Number as well as the Metering Blocks.

The Float Bowls will not be stamped.

Tom V.

[Tom Vaught]

http://documents.holley.com/199r10015-1rev.pdf

Posting this Holley Link again for people who do not want to read thru 14 pages of the posts.

Not as good as the Old Holley Spec Books (Red and Black ones) but covers the most common carbs.

Tom V.

[Tom Vaught]

Just when you think that you have seen it all:

Today I am going to post a few more pictures about Holley Mechanical Linkage Carbs.

Then I will talk about Side Hung Bowls used on the Mopar and Ford Mechanical Linkage 6 pack manifolds. There was a reason why the side hung bows were used.

Then I will show you a picture of a Holley Tri-Power set-up that I would never have come up with but it has some interesting features.

So first I will post up the Pictures. Click on each picture to make bigger

So the first picture on the left shows a nice set of Mechanical Linkage 440 6 pack carbs that could be used on the Weiand "Rat Roaster"
intake manifold. The carbs use the Edelbrock style (Chebby Throttle Linkage) and a metering block with a idle circuit for each carb.
The carbs work really well plus they are large cfm. The Center carb is 355 cfm and the end carbs are 500 cfm each. The center carb has a venturi like a Holley 600 cfm Primary carb and the end carbs have venturis like a 850 cfm 4781 carb. So the real cfm is more like 850 plus 300 or 1150 cfm, not 1350 cfm. The third picture shows the side hung bowl. Apparently the computer posted the 1st pic twice, sorry about that. last pic is the one I will talk about in a bit.

Tom V.

[Tom Vaught]

Ok time to talk about the last Picture in my previous post.

I learned something today.

Here, in the previous post, we have a 6 pack set-up (Tri-Power) on a Weiand "Rat Roaster" intake manifold.

The bare Weiand manifold looks pictures #1, #2, #3 below and there is a drawing from MOPAR Performance on how to fix the poor cylinder to cylinder distribution to the runners when the system is run only off of the center carb.

Lots of effort in trying to get that idle fuel to the runner inlets but difficult because the plenum is flat and not very tall.

So then we go back to post #269.
Here the gentleman mounted up a rat roaster intake on his engine but he did something different. HE IS RUNNING THE ENGINE NORMALLY OFF THE END CARBS. Just like a Pontiac Dual Quad intake would be running off the primaries on a pair of AFBs. So the air fuel mixture is right over the front pairs of runners and the mixture is right over the pairs of rear runners. Straight shot right to the ports cruising down the road.

So then the gentleman needs more cfm so he opens up a 625 cfm 2-barrel in the spot where a normal primary carb would be. That carb is just adding more cfm to the overall plenum at high speeds. So all of the issues the MOPAR guys had with the intake can be fixed by how you think about running the Primary Carbs and the Secondary Carb.

If you look at his linkage you will see that he is opening up the 350 cfm carbs at the same time and then the linkage opens up the Large 625 CFM center carb later on.

Picture #4 shows all of the mods required to the lower intake plenum to get the fuel distribution even close at low rpm and normal cruise speeds.

Tom V.

[Tom Vaught]

Back on Holley carbs and their Calibrations today.

I will be posting up a few "calibration bits of info" today on 4150/4160 Holley Carburetors.
The info would also apply to Holley 4412 2-BBL carbs.

a) Some Holley Carbs have two "Flat Top Plugs" on the top surface of the Metering Block. Others have "Cup Plugs" in the same locations.
The "Cup Plug" Metering Blocks are more of a Performance Metering Block vs the "Flat Top Plug" Metering Blocks.
The "Flat Top Plug" configuration means that there is an Emulsion Tube extending inside the Idle Well to remove volume in the Idle Well and make the circuit more responsive. Great for Driveability, not so good for High Performance applications. Avoid these metering blocks.

b) The Anti-Syphon Bleed also called the "Kill Bleed" in the metering block helps to purge hot vapors from the Idle Circuit and also eliminate syphoning of fuel from the Idle Well. It is typically fixed in size and location.

c) The "Idle Feed Restriction", (also called the "Idle Jet"), is mounted low in the metering block, close to the Main Jets. It is in that location, for a reason. That reason is the "IFR" or "Idle Jet" is submerged in LIQUID FUEL and continually meters that Liquid Fuel. This is the PRIME Idle Fuel Calibration Circuit component.
Holley revised this circuit and moved the IFR to a High Mount Location where it now metered Fuel and Air on later Metering Blocks.
Bad Mistake. Most good carb modifiers put the IFR back where it belongs in the original low mount location.

d) The Idle Air Bleed is the Prime Air Bleed for the Idle Circuit and is located in the upper portion of the Main Body in most carbs and located in the Metering Block Idle Cross Channel on some Modified Carbs where the Carb Guru does not want people knowing what the orifice size is for the specific carb. The Bowtie Guys had some carbs made that had a 'alternate' idle air bleed (in the Air Horn Ring location) but this is not a common location.

e) Some Holley Carbs used a Idle Well Tube (mentioned earlier) that bleeds air into the Idle Well Channel. In this case the bleed air mixes with the idle fuel and creates a homogeneous fuel/air mixture prior to exit thru the idle discharge port hole ot the Transfer Slot location.

More carb info another time.

Tom V.

[Tom Vaught]

The Holley Main System is made up of two major components:
The Annular Discharge Booster Assembly (talking about modern Carb Design stuff vs the old "Straight Leg Boosters" in this post) and the Main Air Well System.

The Annular Discharge Booster Design induces higher air velocities at the point of the discharge which results in increased signal strength to the Main System. The configuration of booster and the size of the booster assembly was established by running signal strength measurements fuel flow curves, and fuel discharge profiles on Holley Engineering's Wet Flow Benches in Warren Michigan.

The total airflow of the carbs was reduced slightly, the target was to have no reduction of airflow. Most Annular Discharge Designs will flow approximately 5 cfm less per booster position so on a 850 cfm carb with the annular boosters the air flow would be 830 cfm.

The Main Well operation is the same as the Idle System.

The High Speed Air Bleed meters the "bleed air" to the Main Well. The "bleed air" is fed thru holes in the metering block (emulsion holes) and form a homogeneous fuel/air mixture that is then discharged thru the Annular Booster assembly.

Obviously the High Speed Air Bleed is a "calibration item". The Main Fuel Jet is the "calibration orifice" for the fuel from the fuel bowl.
The High Speed Air Bleed is determined based on the range of Main Jets determined by the Calibration Strategy and Engine Dynamometer data.

The Idle Jet (Idle Feed Restriction) is determined by the approximate fuel required to power the engine in the Idle and off-idle speed ranges.

The diameter of the Bleed Holes (emulsion holes) and number and position of those holes have a direct effect on the vehicle "drive characteristics"
The Top Hole(s) affect crowd and part throttle acceleration response. The Bottom Hole(s) are used to initiate and accelerate the Main circuit fuel and air flow thru the booster.

NOTE: Changes made to the Air Bleeds, for fuel curve contouring, DO NOT REQUIRE changes in the emulsion holes

A change in the Main Jets will require a potential change in the air bleed holes at times. This is a calibration tuning effect.

If the proper balance between the Main Jets and the Air Bleeds is not maintained, a depreciation in vehicle driveability will result.
The Fuel/Air System of a Holley carburetor may be classified as a tuned circuit carburetor and will be extremely stable and responsive to engine mode changes if proper methods of tuning are observed. A Air/Fuel meter is recommended.

Tom V.

[Tom Vaught]

Starting today, (and probably over several posts) I am going to describe 'ONE METHOD' of how to tune a Holley carburetor.

In the "old days' (when Holley Carburetor was being funded for "Calibration Development" by the Big OEMs: GM, Ford, and Chrysler), Holley had a specific process on how they dialed in their calibrations.

Holley had Horiba Air/Fuel Meter equipment even in the 60s and 70s but it was $$$$ for one set of equipment. It did allow on the road testing of the calibrations though. http://www.horiba.com/automotive-tes...mexa-730-2592/ Today many Pontiac Enthusiasts have the same or better equipment.

So Step #1 is you start off with a Basic Holley Calibration. I have taken apart a very large sample of Holley Carbs over the years and "Finger-Printed" the calibrations as the standard for how that specific "List Number" carb was built.

So in Step #1 we put the Carb back to the specs that the "Holley Carburetor Calibrator" came up with in the first place.

The main parts of the Calibration are:
a) The Idle Jet (also called the Idle Feed Restriction IFR by many people today. I will use "IFR" in the future to describe that Calibration Orifice.
b) The Main Jet
c) The Idle Air Bleed
d) The High Speed Air Bleed.
e) The Main Well "Kill Bleed" (also called the Syphon Break).
f) The Idle Mixture Screws
(These parts are located in the Metering Block or in the Air Horn area above the Main Boosters.)
g) The Idle Transfer Slot is located in the Throttle Blade Base
h) The Idle Discharge Hole is also located in the Throttle Blade Base

You, typically, put the "base calibration" back into the carb, adjust the Idle Mixture Screws to 1.5 turns from lightly seated on 2-corner idle carbs or 3/4 turn from lightly seated on 4-corner idle carbs.

On the 4150 series Holley carbs you set the Transfer Slot Window to about .020" exposed below the Throttle Blade
If you have a "Idle-eze" circuit in the carb you open that up to allow the engine to idle above typical Idle RPM initially
If you do not have a "Idle-eze" circuit you open up the air gap on the Secondary Throttle Blade Stop slightly.

Hopefully BEFORE you started the Holley Carb Tuning, you verified that the Engine Initial Spark Timing was to specification and the parts were in good working order.

You KNOW that you have good Fuel Pressure to the carb (measured with a Proper Fuel Pressure gage) and hopefully set to 6 psi
Holley Calibrators love 6 psi fuel pressure settings, higher or lower, they are not so happy as excessive fuel pressure raises the fuel level in the fuel bowl, changes the fuel level in the Main Wells and Idle Wells, changes the point of "Start-up" of different fuel/air circuits, and simply confuses the heck out of things. The 6 psi fuel pressure setting was specified for a reason.

More on tuning later.

Tom V.

[Tom Vaught]

Tuning the Transfer Slot in Holley Engineering.

The Transfer Slot (many times made by a EDM process) is typically in the range of .190" tall by .025" wide.
You have a general TS location and then the Slot is raised .020" and then lowered .020" on different carbs to find the "Sweet Spot" for that specific Throttle Bore/Throttle Plate diameter.
The "Early" and "Middle" sections of the "Off-Idle" Fuel/Air curves are primarily affected by these changes.
(The Idle Mixture Screws are always adjusted for each change to allow consistent Data Change comparisons.)

The Idle Feed Restriction (Idle Jet) is varied +/- .002" but the Idle Air Bleed Holes (Restrictions) are not changed when the IFRs are changed.

A Change in the flow curve initiated by the large IFR suggests that driveability would be improved, BUT that assumption could be wrong in actual testing and the drive modes could be poorer in modes below 30 mph. There is always a "give or take" in calibration tuning.

Changing the Idle Air Bleed (-.005" and then +.005") without changing the IFR may not significantly affect the Idle Set Point but the drive modes below 30 mph will be affected. Again there is a balance in what is acceptable.
"Balancing" the IFR and the Idle Air Bleed takes time but is worth the effort. The Idle Mixture Screw may have to be adjusted slightly to get back to the original Idle RPM Set Point.

Changing the Idle Air Bleeds upward, at times does improve the overall drive and Power modes of the carb. Cliff Ruggles found this out on his Holley 4781--2 carb when he increased the Idle Air Bleed size slightly and the overall performance was better.

That carb later went on the Engine Dyno and the Dyno people told him to "never touch that carb, it was perfect".

More info Tomorrow.

Tom V.

[Skip Fix]

I remember the old Rat Roasters. I think there was a dual quad one also for the Hemis

[Tom Vaught]

You are correct Skip.
Pics attached. I have only seen one Hemi Rat Roaster modded for a 6 pack set-up and they basically welded in a rectangular plate with 3 carb spacers in the top cover. Never saw one that actually ran on a Hemi.

Tom V.

[Skip Fix]

I think I saw one on a Hemi back at the '72 IHRA races I ran in in their formula stock class.

[Tom Vaught]

I am not a big fan of copying images from People's Books. I really like David Vizard's info that he puts out on Holley carburetors.

Today I am going to provide a link (lots of Pics and good info) on how a Holley carb basically works. So today's post is about the theory/physics of a Holley carburetor.

David does a much better job than I could.

Here is the link.

https://www.cartechbooks.com/techtip...ng-principles/

If you have questions post them up and I will give it a shot on explaining the theory.

Tom V.

[Tom Vaught]

"Back in the Saddle" tonight for a bit of time.

I had a PY Member send me a PM asking about the Tri-Power Linkage I can up with for my Holley carb set-up using the Barry Grant Holley Intake Manifold.

I will post a picture or two of the way Ford did their Tri-Power Linkage, I will post up a Holley Set-up copying the Pontiac Tri-Power linkage, and I will post up a Pic of other linkage ideas.

This might take 3 posts by the time I post up the pictures and explain each set-up.

So here we go:

So the first picture shows a Pontiac Factory Tri-Power Linkage that connects the two end carbs (that most are well aware of).
The second picture shows a Ford Factory Tri-Power Linkage with the difference being ALL of the carb linkage is on one side of the carburetors. You have a center carb lever and you have end carb levers clearly shown in the picture.

TWO OF THE THREE PICTURES BEING FORD CARB LINKAGE BUT THERE IS A DIFFERENCE IN THE CENTER CARBS LEVER.

The middle picture shows the curved center lever and the third picture shows the "upside down" "L" linkage arm.

Tom V.

[Tom Vaught]

In this second post we will show the Pontiac Tri-Power Linkage from the drivers side and then some shots of holley carbs with a similar linkage.

So the first picture clearly shows the Pontiac center carb to read carb slotted rod and lever arms.

The second picture shows a similar "one off" linkage for the Holley carbs with the slotted rod on the one side and a heim joint/solid rod
connecting the rear and front carbs. The only difference being the much beefier rear to front carb connector rod.

The third picture just shows a different lever arm on the rear and front carbs.

Tom V.