[Tom Vaught]

ONE MORE VERY IMPORTANT POINT, SRR AND OTHER HOLLEY PEOPLE.

NEVER NEVER NEVER RUN THE CARB ON A ENGINE WITH THE TWO PHILLIPS HEAD SCREWS IN THE CENTER OF THE CARB.

Ok to have the 3 phillips head screws closest to the metering blocks installed on both sides BUT the phillips screws between the front barrels and the rear barrel(s) should never be installed. The base gasket between the main body and the throttle baseplate will seal fine without them. I have seen several cases where one screw came out and went into the engine. New Holleys (since the late 70s) do NOT have those screws installed.

Tom V.

[JUDGE3]

Originally Posted by Tom Vaught

Ifn you have a 88 rear jet with the Power Valve, put in a PV Plug and go up 6 Jet sizes more and see how it runs. 6 sizes normally works on less than Dominator carbs. It will be fine with the PV Plug in the rear. Glad to help.

Tom V.

did the above, ran poorly. reverted right back to rear 6.5 power valve, 87 front, 88 rear, .40 squirters f&r ran great. satisfied with that, but why plugging and jetting up made it worse? even backfired a little.

[Tom Vaught]

Haven't been doing much typing lately, had a eye issue with an eye irritation in the left eye.

Once I get this squared away will be back to post more in-depth HOLLEY answers again
Tom V.

[Tom Vaught]

Still trying to get the eye irritation in the left eye fixed up but thought I would add a bit more info on Holley carb theory in general. Some of this GENERAL info was taken from the February 1965 Car Craft article written by Don Francisco who was a great automotive theory writer.
The basic PHYSICS did not change after 53 years but the words used to describe carburetor circuits have changes somewhat.

" An Internal Combustion Engine is one in which the energy is a fuel, usually a liquid that evaporates slowly at normal temperatures and atmospheric pressures." TRUTH

"In its liquid form, gasoline will not burn, nor will the gas resulting from its evaporation until it is mixed with the correct proportion of AIR." TRUTH
"The small percentage of Oxygen in the air - (approximately one-fifth) supports combustion, and the mixture can burn with sufficient speed to be classified as an explosion" TRUTH

"When a mixture of oxygen and gasoline vapor burns in the engine's cylinder, a chemical change takes place in the oxygen and gasoline, and heat is created." TRUTH

"The chemical change produces several gases but the main two are Carbon Dioxide and Water Vapor". TRUTH

"As the HEAT of COMBUSTION raises the gases temperature, the GASES EXPAND and force the cylinder's piston down the cylinder and the piston's connecting rod rotates the engines crankshaft and the car's driveline." TRUTH

So here comes the KEY STATEMENT:

"The greater the WEIGHT of the AIR-FUEL MIXTURE in the cylinder before COMBUSTION, the HOTTER the COMBUSTION will be, and the more tightly the MIXTURE IS COMPRESSED, and the greater will be the PRESSURE that acts on the PISTON." TRUTH

So what did we learn from the words above?
1) That Carburetors control the MASS of AIR and FUEL that enters the engine (based on a control valve called a throttle blade).
2) The Carburetor has to MIX the correct ratio of air and fuel or the mixture will not explode and force the piston downward in the cylinder.
3) The carburetor has to have the ability to compensate for changes in the Mixture Ratio depending on the engine load vs the throttle blade position.
4) "Changing the liquid gas (fuel) into a GAS (VAPOR) and mixing the correct amount of air with that gas (vapor) so that the resulting mixture will burn in the engines cylinders are the DUTIES OF A CARBURETOR.

Mr Francisco says that there are 5 circuits or systems in the carburetor that allow it to do its job.

I will talk more about that as I continue to post his info vs current day knowledge.

Tom V.

[Tom Vaught]

Reading thru his article he says the 5 circuits are:
a) The Idle Circuit
b) The Cruising Circuit
c) The Power Circuit
d) The Acceleration Circuit
e) The Choke Circuit.

Different wording but basically the same as a Holley carburetor. He was and I am speaking in general terms here.

Most today say that the idle circuit is controlled by the throttle position and mixture screws and the off idle performance by the Transfer Slot vs the throttle blade position. Mr Francisco calls the Transfer Slot the Idle Upper Discharge Port. Again just a difference in wording.

Mr Francisco defines the Cruising Circuit as being the point where the Carbs Booster (Nozzle) starts to function and fuel is pulled thru the main jets.

Mr Francisco spends little time on the Power System (except for a mention of metering rods used un some cars to allow more fuel at WOT conditions. He does spend a lot of time talking about Multiple Carb set-up to get the addition fuel required at WOT.
For the Tri-Power Guys apparently he really liked Tri-Power Carb Systems and how they drove on many engines.

Very few Pontiac Guys are playing with the Tri Power Holley Carb systems but but a few of us are out there with those systems.

Mr Francisco does a nice job on the Air Density vs Atmospheric Pressure portion of his article and also does a nice job on the the importance of syncronizing carb linkages on multiple carb set-ups. 4 carb and 6 carbs set-ups were a favorite of Hot Rodders in those days. Sometimes 2G Rochesters but also single bore carbs too.

Tom V.

[Tom Vaught]

I will have to look at a few more of my 50 year old magazines and see what else Mr Francisco wrote about compared to today's performance parts (Holley possibly).

Tom V.

[Tom Vaught]

A bit of a summary of what wer have covered in the past in this thread.

A) Fuel Bowls
1- Sight Glass heights
2) Umbrella Seal vs Check Ball Accelerator Pump systems and mods to the Umbrella Seal Installation rubber tip.
3) Fuel Level in the Fuel Bowl and Types of Floats used for different applications
4) Adjustmenty of the fuel float using visual methods, gage methods, and Needle & Seat "Nut Flats" to adjust the level of the fuel in the bowls.
5) Difference in Sight Hole Heights in the front and rear bowls vs Dominator Bowls.
6) Accelerator Pump diaphragm sizes, spring heights, Pump Arms, pump covers and screws, Pump Cams, and Pump Adjustments.
7) Bowl Screws Lengths and applications.
8) Bowl Venting: Brass vs Plastic whistles, whistle lengths, whistle clearances vs float.
9) Bowl Inlet Fuel Nuts and Bowl Types (race vs Side Hung)
10) Double Pumper Bowls vs Vacuum Secondary Bowls.

More Tomorrow.

Tom V.

[Tom Vaught]

B) Metering Blocks
1- Posted up Pictures of what the different "Holes" in the metering Block(s) do. Where they go to and what fuel circuit that work with.
2) Posted up description of the IDLE FEED RESTRICTIONS and the benefits of the "Low Mount" IFRs vs the later "High Mount" IFRs that mix air and fuel differently and have known issues with Holley calibrations.
3) Idle Mixture Screw Adjustments
4) Transfer Slot vs Throttle Blade Adjustments,
5) Power Valve Function and Adjustments
6) Power Valve Channel Restrictions and how they control Power Enrichment on the Holley carburetors.
7) Accelerator Pump Passage identification and merits of different designs.
8) Spark Port Passage identification and how it is machined.
9) Different Holley Gaskets and Bowl Screws used with Metering Blocks vs Metering Plates.
10) Modifications to 2 Circuit Holley carbs to make 4 Idle Circuit Holley Carbs.
11) Emulsion Circuits, How they work, Why 2 hole circuits vs 3 hole, 4 hole, 5 hole Metering Block circuits.
More Tomorrow.

Tom V.

[Tom Vaught]

So in the past we:
1) Compared Throttle Plate Machining between "2 Corner" Idle Circuits and "4 Corner" Idle Circuits.

2) Discussed the Throttle Plate Numbering system Holley uses for their carbs Double Pumper and Vacuum Secondary: Example:
Vacuum Secondary 750 and 780 carbs typically have #172 Primary Blades and #173 Secondary Blades.
Double Pumper Carbs from 650 cfm to 800 cfm
the same throttle blades for the Primary and Secondary sides of the carbs. The Blade Diameter is 1-11/16" Blades in all 4 locations.
The 850 CFM #4781 Carb uses 1-3/4" Throttle Blades in all 4 locations.

3) 750 Double Pumper carbs are rated at 20.4" of water Test Pressure when flowed. They are rated at 950 cfm with tested at 28" of water but the carb still flows 750 cfm at the Holley Test Spec of 20.4" of water used for 50 years of carb testing.
Same deal for the 850 cfm carb vs the higher rating 1000 cfm rating. Just the test pressure point changed, the carb still flows 850 cfm at the Holley spec used for 50 years. It is all a Marketing trick to get a buyer thinging he has a larger flowing carb when he takes off his 850 cfm carb and installs the 950 cfm carb which actually flows less cfm.

More Tomorrow.

Tom V.

[ta man]

You wouldn't believe the amount of times I get asked carb size and I have to explain my 950hp. For a basically a box stock carb..other than a 50cc pump on the front it works pretty decent.

[Tom Vaught]

Basically a "Non Choke" 4779-6 or later "4 corner idle" carb, that does work very well.

People had a hard time understanding or converting Superflow 25" Water Test pressure vs 20.4" Carb flow numbers, so people took a comment that Smokey made about some testing on his stuff at 28" of water test pressure and suddently the New Standard (the same for heads, carbs, etc allowed bragging rights with one flow pressure number used.

At the end of the day you are running 10.77 with a 750 cfm carb which is darn good no matter what carb cfm people want to use for marketing.

Tom V.

[Tom Vaught]

I have posted on the White Fuel Bowl Vent "Whistles" in the past. How to modify them when using the carb under hard acceleration with good tires so that the fuel does not come out of the carb vents and put a slug of fuel into the venturi area.

This thread today in the Street Section has some nice pics on the original style Holley Bowl Vent Baffle (2nd Generation - Plastic) Original carbs used a metal part.
So here is the link: http://forums.maxperformanceinc.com/...d.php?t=818008

Tom V.

[Tom Vaught]

Been a while since I posted on Holley carbs so thought I would post on a article that was in the STREET RODDER Magazine back in March 2018.

The article is by Jeff Smith who apparently was a Contributing Editor for this Small Block Chebby/Holley Tri-Power article. (The point being some Pontiac Guys might buy the Carbs used on the SB Chebby manifold and assume that they can use them on a Ames Performance Tri-Power Intake (with adaptors).

I have done the adaptor deal from Rochester 2-BBLs to Holley 2BBLs several times. I prefer the Mopar carbs for the 440 or the Chebby 427 (390 & 435 HP engines).

This article is about the Holley carbs installed on the Chebby engine and why the engine made less HP vs a single 750 cfm carb.

Dyno numbers for the 750 cfm carb were:
431 HP at 6000 rpm and 424 lbs/ft of torque at 4000 rpm

Dyno numbers for the Tri-Power carb set-up were:
411 HP at 6000 rpm and 405 lbs/ft of torque at 4000 rpm. (this is with carbs that Jeff Smith said flowed a total of 1025 cfm thru them.
So WHAT HAPPENED???????????

1) 2-BBL carbs (as mentioned in a previous post) are rated differently vs a 4 BBL carb.

The 4 BBL carb is tested at 20.4" of test pressure on the flow bench.

The 2 BBL carb is tested at 40" of test pressure on the flow bench.

So if you have a center carb rated at 325 cfm and the end carbs rated at 350 cfm, you get 1025 cfm total. But it does not work that way if you are doing dyno testing on the same engine but with carbs rated at different test pressures.

Using the formula: 2 BBL cfm at 3" divided by 1.414 = 4 BBL cfm at 1.5" (4 BBL cfm test pressure).

325 divided by 1.414 = 230 cfm
350 divided by 1.414 = 248 cfm times 2 = 495 cfm

495 cfm plus 230 cfm = 725 CFM (NOT 1025 cfm like the article states.

So the dyno numbers make perfect sense due to the reduction in cfm when using the Tri-Power Holley carbs sold for the SB Chebby Intake.

Now if you bolted on 3 of the Holley 2 BBL Carb #4412 rated 500 cfm at the 40" of test pressure you would have not 1500 cfm but 1061 4-BBL cfm so the system would be slightly more cfm vs a 1050 Dominator carb set-up. With that you could make some Dyno Horsepower.

Hope this helps when reading magazines having Holley carb tests in them.

Tom V.

[Tom Vaught]

I have posted about the Holley 3-BBL carb in the past but want to add some additional info on this carb.

Back in the June 1966 time frame, Holley was doing some carb testing on the Holley 3-BBL carb. The idea of the 3-BBL carb was not new, Jon Hargrove could tell you a story about a 3-BBL AFB that Pontiac Motors and Carter Carburetor came up with a few years earlier.

This carb was larger in actual air flow vs the largest typical Holley carb at the time, the #3310 Holley 780 cfm carb. There were some 850 cfm carbs out there too. Chevrolet actually offered a vacuum secondary 850 carb at one point. But back to the 3-BBL.

The new #3916 Holley carb flowed an actual 950 cfm on the Holley Carb flow bench in Warren Michigan.

So how did it do on the engine dyno?

With a Edelbrock "3-BBL intake installed (rear intake barrels had a notch cut into the plenum divider for 3-BBL throttle blade clearance) the carb/intake was worth 33 more HP over the typical 780 carb and intake at 5000 rpm.

The #3916 carb was 8 tenths of a second faster on acceleration runs on the street.
The Edelbrock #3916 testing used #80 jets on the primary and drilled .086" read orifices in the metering plate.

The actual dyno HP differences were:
31 Hp @ 4500
33 Hp @ 5000
33 Hp @ 5500
25 Hp @ 6500
20 Hp @ 7000

Edelbrock wanted to sell the intake to go with the 950 cfm carb so they cut a deal specifying that the only way you could get the carb was by buying the Edelbrock intake at the same time.
Motion Performance ran a lot of these carb/intake set-ups on their modded chevy engine packages.

Tom V.

[Tom Vaught]

It has been a while since I posted on the Holley Carburetor Thread so I thought I would post up some information about what a Engine wants in the way of "Carburetor Requirements".

A lot of this info has been posted over the years, or included in books, but the Engine PHYSICS does not change on the internal combustion engine.

This info (as my boss at Holley - Mike Urich - used to say) will not be a bunch of tough mathematical formulas. I will try to make it "dirt simple" like he wrote in one of his books. He also used to say, the Engineers who work for me can do the complex calculations when they design the carburetors.

Question #1:
How big should the Carburetor Be?

Easy enough question once you admit that every engine is different and therefore "It Depends".
It depends on the following parameters:

1) Engine Displacement
2) The Type of Engine
3) The Maximum RPM of the Engine
4) And finally How EFFICIENT is the engine moving Air and Fuel Mass thru the internal Conduits (Runners, Ports, and Valves).

1) Engine Displacement can be expressed in either Cubic Inches or in Liters. As of 2018, Liters is more often used by Engineers and Cubic Inches by RACERS.

2) The Type of Engine can be either a 2-Cycle Engine or 4-Cycle Engine. I simple terms a 2-Cycle engine has a Intake Stroke every revolution of the crankshaft and a 4-Cycle Engine has a Intake Stroke every other revolution of the crankshaft.
Older PY Members know this stuff already but some PY members may be new to how a "engine works".

Maximum RPM is simple how high are you going to spin the engine vs how high can the engine run with the parts it has before it hurts itself and costs you money to repair or replace parts.

For a 2-Cycle Engine the simple formula is:
Cubic Inch Displacement (CID) times Volumetric Efficiency times RPM = "X"

One Cubic Foot of air is a square 12" long by 12" deep by 12" high or 12 x 12 x 12 or 1728 total inches. So One Cubic Foot of Air "Y" = 1728

CFM = X divided by Y

For a 4-Cycle Engine the Formula is different.

Cubic Inch Displacement divided by 2 times Engine RPM divided by "Y" = CFM.

An example:

350 Cubic Inch Pontiac Engine
5000 RPM maximum
Volumetric Efficiency = 1 at that rpm.

350 times 5000 = 1750000
2 times 1728 = 3456

1750000 divided by 3456 = 506 Cubic Feet per minute of air mass passing thru the engine.

More on this later. Specifically on the DENSITY OF THE AIR

Tom V.

PS Same Calculation if you had a 350 Chebby Engine revved to 8000 rpm

(350 times 8000) divided by (2 times 1728) or 2800000 divided by 3456 = 810 cfm.

That was a simple math calculation.

The actual Volumetric Efficiency will be closer to .75% or .85% for a naturally aspirated engine.

So then you would add one more step to the calculation and multiple the 810 cfm times 75% or 85%

There are calculators out there but nice to know how the calculations work.

[Tom Vaught]

I will post a little more about Volumetric Efficiency tonight in this post.

Volumetric Efficiency indicates how well an engine "Breathes".
Volumetric Efficiency is really a incorrect term for what is really happening.

Mass Flow is what really counts. But because people have used Volumetric Efficiency there is no real reason to Change to MASS EFFICIENCY.

In the BOOST Forum we can talk about MASS FLOW (because under BOOST conditions the MASS FLOW goes up while the Volumetric Flow remains the same as a Naturally Aspirated engine).

So V.E. (mass) is The Actual Mass of Air taken in (divided by) the Theoretical Mass of Air which could be taken in.

Highest Volumetric Efficiency reaches a high point close to where Maximum Torque occurs.
It does not follow exactly but many people assume that they are the same thing.

Stock Engines have a V.E of about 75%.
High Performance Engines have a V.E. of about 80% at max speed and 85% at max torque.
A Racing Engine can have a V.E. of 90%+ at max speed and a V.E of over 95% at max torque.

Again if we are talking DENSITY of the Air then V.E can be expressed as the Density in the Cylinder divided by the Density of the Ambient Air entering the engine.

IDEAL MASS FLOW FOR A 4-CYCLE ENGINE IS CALCULATED BY:

(ENGINE RPM DIVIDED BY 2) TIMES (CUBIC INCH DISPLACEMENT) TIMES (INLET AIR DENSITY).

Note: Air Density varies inversely with Pressure so:

The Lower the Pressure, the LESS DENSE the Air.

More Tomorrow.

Tom V.

[Tom Vaught]

I have posted about the Density of Air in the past several times.
My old boss had a simple calculation to find the Density of of a Cubic Foot of Air by using a Barometer Reading and a Temperature Reading.

The Formula was Density of Air in Pounds per Cubic Foot

1.326 times for example 29.92 Inches of Mercury
divided by
Temperature in degrees Fehrenheit + 459.6

So 1.326 times 29.92 Hg = 39.35568
85 Degrees F + 459.6 = 544.6

39.35568 divided by 544.6 = .07226 pounds of air mass per each cubic foot of air that is entering the engine.

There are slightly more accurate calculations and calculators out there but this formula is not costing you any money. And you can use it to document your track numbers vs the air entering the engine. Just remember that the Barometer Number must be an uncorrected number.

I will try to post up a couple of simple carb fuel calculations later today.

Tom V.

[Tom Vaught]

Noticed my cheap Calculator does not agree with my excel file.
Try it again.

So 1.326 times 29.92 Hg = 39.67392
85 Degrees F + 459.6 = 544.6

39.67392 divided by 544.6 = .07285 pounds of air mass per each cubic foot of air that is entering the engine.

Tom V.

[Tom Vaught]

Air Flow and the hundreds (if not thousands) of calculators on the web plus the different member locations make it very difficult to discuss that subject in generic terms.
When my boss wrote his 1st book the web was primarily used by the government and by universities to do simple modeling.

I have found nothing to change in the simple calculations in the Holley Books for what the average enthusiast wants to calculate. As I posted before, I will leave the higher level calculations for the carb designers.

Tom V.

[Tom Vaught]

Wallace Racing has a calculator you can play with
http://www.wallaceracing.com/air-fuel-lambda.php
that will give you an idea of how Fuel/Air and Air/Fuel ratios work.

Tom V.