[Tom Vaught]

Going to talk a little bit about "Uniform Distribution".

"Uniform Distribution" means "Equal" Fuel and Air Distribution to the various cylinders.
"Non Uniform Distribution" means "Unequal" Fuel and Air Distribution to the various cylinders. It causes a loss of power and efficiency in the engine.

"Uniform Distribution" assumes a number of things:
a) Good atomization of the fuel from the carburetor to the runners and cylinders.
b) Use of proper fuel of the correct volatility for the "seasons" the engine and fuel system will be exposed to.
c) Using proper methods of engineering/ techniques to assure vaporization of the fuel.
and finally
d) Using a proper intake manifold design.

One thing that a lot of people miss is that Idle Fuel is typically 10 to 20% richer than "Ideal" to offset exhaust gas dilution.
If the carb were to be required to pass emissions requirements that would demand that ALL of the cylinders were receiving basically the same fuel/air ratio.
A Intake Manifold with poor distribution would basically cause the engine to be excessively rich on some cylinders to be able to run and that would cause the engine to fail the emission standard. ALL of the "Pieces of the Puzzle" are important.

If you were after maximum fuel economy then the fuel/air ratio would be about .06 and all cylinders receiving the same fuel/air.
If one cylinder was lean then the rest of the cylinders would have to have a richer fuel/air ratio for the lean cylinder to have the proper fuel/air mixture to fire properly.
So the lean cylinder (poor distribution) has messed up the operation of the other cylinders. This is where EFI with an injector for each port and proper fuel/air distribution is actually better vs a typical carb and normal intake manifold.

A fuel/air distribution of .075 is very close for the maximum power target.
You have the same issues at max power as at idle with the one lean cylinder except that now that lean cylinder need to be made richer to avoid detonation.

Of course again the other cylinders will now be over-rich as far as making best power from the engine.

One final comment tonight, Unequal distribution not only affects idle and power but also has an impact on timing used in firing the spark to the cylinders.
If you have unequal fuel/air distribution then the ignition timing curve for the engine can only be a compromise at best. The amount of Timing Advance can only be the amount the leanest cylinder can support without producing knock. Again a EFI and Modern Individual Ignition System for each cylinder can bring back a lot of the power lost in the above discussion.

Have a good night. I was an Engine Systems Calibrator for several years in my previous job.

Tom V.

ps People always tell you that Flow Benches don't really tell you anything except for a FLOW number to brag about.
That is true if you use the thing for bragging rights in intake and head FLOW discussions.
If you use it as a tool to optimize the fuel/air distribution in the engine then you are using the tool properly.

[Tom Vaught]

Some of the ways that you can check for proper distribution is by using:

a) Chemical Analyzing exhaust gas (combustion products) samples from the individual cylinders during different engine dyno modes: Idle, Cruise, Acceleration, Maximum Torque, Maximum Power, Maximum +10% Torque, Maximum + 10% HP and finally at Maximum Economy Points.

b) Measuring Exhaust Gas Temperatures (EGT Thermo-couples normally used for this).
This is done by inserting a Thermo-couple into each Manifold Exhaust Port or Header Port .
The Dyno Operator looks for "EGT Peaks" at various modes by changing main jet sizes or fuel injector duty cycle settings.

Rarely are all Cylinders the same because of differences in cooling, valves, porting, and ring sealing.

Perfect Distribution would put all cylinders at their peak EGT Temperatures with the same carb jetting which by the way is RARELY ACHIEVED.

Time to do some home projects. Later.

Tom V.

[Tom Vaught]

I will make a few comments tonight on fuel and its ability to be ignited by a spark or by a flame.

Before Gasoline (or other fuels) can burn Vaporization of the fuel is required.
Vaporization converts the fuel into a gas state and this only happens when the liquid absorbs enough heat to boil.

Temperature and Pressure relationship comes into the discussion.
Water for example will boil at 212 degrees F and at sea level conditions.

Take the same water and try to boil it at Denver and it will boil at a lower heat temperature.

In cold weather the fuel has a harder time of vaporizing and the fuel burning which is why you have heated intake manifolds.

Obviously you would think the higher the temperature the better the fuel vaporization, (but the reality is if all of the fuel is vaporized there will be a loss in power of the engine.
The Charge Density goes down. You have a smoother running engine but with less power.

On a engine with a carburetor, the intake manifold walls will always have some fuel clinging to the surfaces. When you accelerate the fuel gets removed from the walls for an instant. That fuel needs to be replaced or you get a lean condition in the engine.
The accelerator pump circuit replaces the fuel on the walls with new fuel and adds a bit of extra fuel to the intake charge for a slight period of time. Not enough fuel replaced and you get a engine hesitation.

One final comment for tonight:
Imperfect Vaporization may occur if:

a) The Mixture Velocity is too low
b) The Intake Charge is too cold
c) The Manifold Vacuum is too low
d) The Fuel Volatility is too low for the ambient temperature.

Have a good night.

Tom V.

[Tom Vaught]

A Bit more Carb PHYSICS today in my post.

1) Gasoline which comes out of the Idle Discharge Port (below the Throttle Plates) enters the air stream of the carb. When the fuel comes in contact with the air it is torn apart into a large number of very fine droplets and resembles a fine "Mist".

2) Ideally you would like that "Mist" to be 'Vaporized' or changed to a gaseous form.
Because the fuel and air mist are below the throttle plates the Pressure will be much LOWER vs Atmospheric Pressure under the hood.
This much lower pressure, as was said before changes the Boiling Point" of the mixture.
Some of the fuel particles are 'vaporized' as they absorb heat from the surrounding air.
Some of the fuel particles are 'vaporized' as they absorb heat from the Hot Spots in a heated intake manifold.
Some of the fuel particles just attach themselves to the colder intake manifold walls.

3) Imperfect Vaporization
a) You get Imperfect Vaporization when you have a "cold" intake manifold.
b) You get Imperfect Vaporization when you have a "cold" Ambient Temperature.
c) You get Imperfect Vaporization when the intake manifold vacuum is too low.
d) You get Imperfect Vaporization when the intake manifold design is poor or the Carburetor size is too large for the engine.

4) Why is a Larger Carb an issue?

a) With the same engine speed (RPM) the air charge velocity thru the venturis is lower,
therefore a lower "Pressure Drop" across the Discharge Nozzles (Boosters) in bigger "Chunks/ Blobs/ Globs/ or Drops" and those Larger Drops are much harder to Vaporize.

b) In the case of a 2-BBL or 4-BBL carb with Progressive Secondary Throttle Blades, the fact that you have fewer of the Throttle Blades open makes for HIGHER VELOCITY across the Throttle Blade(s) that are open.

c) Smaller Throttle Blade Diameter/ Venturi Diameter makes for Higher Velocity across the Venturi and Higher Velocity and Better Atomization of the fuel charge.

** The Pontiac Tri-Power with its small Center Carb Venturi 1-1/4" on a 64-65 Carb allows great Intake Charge Velocity across that carb and you still have the available CFM capability from the End Carbs. TV

d) Dual Quad Carbs on Open Plenum Intakes with all Throttle Blades opening at the same time will have the lowest intake charge vaporization and of course the roughest idle.

Manifold Design (as mentioned above) has a direct effect on how much of the fuel is not vaporized and therefore is attached to the Intake Plenum Walls. If you open the Throttles, the fuel on the walls comes off and then you need Multiple LARGE Accelerator Pumps to replace that fuel back on the plenum walls or you will have a hesitation after opening the Throttles quickly.

Enough PHYSICS for a while.

Tom V.

[Tom Vaught]

A Couple of "Tips" if your application is primarily Max or Near Max RPM modes of operation.

1) High Mixture Velocity thru the manifold will help with good distribution to the cylinders along with doing a better job of vaporizing the fuel in the air stream and will help retain the smaller particles of fuel in suspension in the Air/Fuel Mixture.

2) Below Near Max or Max rpm speeds some form of manifold heating is recommended.
The fuel needs to be vaporized by some method. Cutting of the Pontiac Intake Manifold at the water cross-over actually removes engine heat that would come from the engine coolant system. The same would apply with the blocked heat cross-over when used on a street driven vehicle.

One thought I have had was to add the common air purge lines at the back of the heads and run that low volume heated water thru the heat cross-over of the intake manifold AFTER the intake manifold openings (to the heads) were welded shut.

From there the water would exit the now heated WATER CROSS-OVER and travel to the Thermostat Water Cross-over before traveling to the radiator. The small volume of water (heat) would help vaporize the fuel (180 degree water temp) vs the normal 1350 degree exhaust gas heat that normally passes thru the manifold cross-over between the two heads.

Tom V.

[Tom Vaught]

Last comment for the night.

Mike Urich, in one of his books mentions the effect of having the throttle blades close to the roof of a Intake Manifold Plenum vs having some "distance" from the Carb Base/Throttle Blades to the Pluenum.

Holley Carb Engineering testing on Engine Dynos showed a definite benefit in fuel distribution in the intake manifold by adding a 1-1/2" to 2" Spacer between the carb and plenum when using a dual plane intake. (The lower level plenum ALWAYS had better fuel distribution in the intake runners vs the upper level plenum without any spacer.)

The fuel distribution was basically equal on both upper and lower plenum after the 4 hole spacer was installed.

Tom V.

[amcmike]

Originally Posted by Tom Vaught

A Couple of "Tips" if your application is primarily Max or Near Max RPM modes of operation.

2) Below Near Max or Max rpm speeds some form of manifold heating is recommended.
The fuel needs to be vaporized by some method. Cutting of the Pontiac Intake Manifold at the water cross-over actually removes engine heat that would come from the engine coolant system. The same would apply with the blocked heat cross-over when used on a street driven vehicle.

How important is this if you were running annular boosters vs. straight or downleg, since the atomization would be better?

[Tom Vaught]

Agree, The atomization would be better with the Annular Boosters, especially the 12 hole ones.
The 8 Hole Annular Boosters are still better than the Straight Leg Boosters.

It kind of depends on how much better if the Straight Leg or Down Leg Boosters have Shear Steps, etc.
Manifold Heat seems to work all of the time and booster tricks work sometimes really well.
Annular Boosters do suck up cfm but do have a better driveability.

I assume you are going to lose between 5-7 cfm per booster vs a Down Leg Booster.

Tom V.

[Tom Vaught]

Personally I am a fan of the carbs with Annular Booster installed.
These carbs would be the 850 CFM carbs, or in some small engine cases, the 750 cfm double pumper carbs. But now you are getting into 750 cfm carbs that actually only flow 730 cfm. These would be street engines wanting excellent drive on the streets or Ski Boats, where you want the engine to respond immediately to the throttle (to pull the skier out of the water).

So for ideal DISTRIBUTION you want:

a) Vaporize as much fuel as possible so that the minimum amount of liquid fuel is present in the cylinders.

b) Use fuels with the correct Volatility for the ambient temperature and altitude conditions.

c) Ensure that the Charge Velocities are kept high in the intake manifold by using the smallest possible passages consistent with the desired volumetric efficiency and Hp.

d) Provide good atomization in the carburetor by selecting the proper venturi size (and carb flow capacity).

e) Avoid at all cost, Heads and Intake manifold constructions which allow fuel to separate out of the mixture due to sharp corners, "S" bend passages, and severe changes in the cross-sectional area.

f) Provide Turbulence in the manifold and head design to ensure that the fuel and air are kept well mixed during their passage to the cylinders.

g) Provide Manifold Heating, or heating of the air, to ensure that the fuel is well vaporized.

Tom V.

Note: Boosted Engines (especially Centrifugal Superchargers and Turbochargers) when used to pressurize carburetors (by using Inter-coolers) can optimize the conditions for proper Fuel/Air Vaporization.

[Tom Vaught]

Thought I was doing good on this thread and everyone was happy with the info.
I see that someone knocked me back to a 3 star on the topic.

Guess maybe it is time to end the posts.

Tom V.

[amcmike]

Originally Posted by Tom Vaught

Thought I was doing good on this thread and everyone was happy with the info.
I see that someone knocked me back to a 3 star on the topic.

Guess maybe it is time to end the posts.

Tom V.

I didn't even know we could rate posts till you said that... added a 5 star (well deserved IMO), but looks like it didn't move the needle much. Just forget the haters. They can move on.

The info. is extremely valuable. Nice to have an expert that knows what they're talking about. Not just the hardware, but tuning as well. And maybe, (just maybe) it'll prevent a carb or 2 from getting hacked up by some "expert" that "thinks" they know how to make the carb "work better" on the engine.

Actually that might be a good topic... what NOT to do to a Holley. I'm sure you've seen/heard some wild stuff. Like drilling out jets to increase flow, removing the inlet filter, or removing the check ball on the secondary diaphragm.

[Tom Vaught]

Think that would be a good topic at some point down the road Mike.
Agree there are a lot of mods that can really either do nothing or screw up the carb from ever performing well after modifications.

When I first came to Holley in the 70s, I was part of a group that was documenting the mods made by "Modifiers" and sold to the public. So Holley had a bunch of workers at the Engineering Center in Warren, Michigan order carbs from "Modifiers" under their own names and Holley reimbursed the employees for the cost of the purchases. At the end of the Purchasing time-frame, Holley Engineering had about 20 "Modifiers" Carburetors.

So the next step was to take the carbs, AS RECEIVED, and put them on the "Air Boxes" and Check the "Calibrations" on each carb against the 'Holley produced' matching List Number carb from Holley.

After that each carb went on a "small block" Chevy dyno engine (10,000 engine rpm capable water brake dyno) and the two carbs (the "Modified" carb and the "Holley out of the box" carb were tested back to back in all phases of the carburetors operation.

At the end of the testing, THREE "Modifiers" carbs were slightly "Better" vs the "Out of the Box" Holley Carbs. But the $$$ paid for the Modifications vs the $$$ spent vs the Benefits in HP and Torque might make a few people unhappy.

Most of the Modifications was "Smoke and Mirrors" vs real carb improvements.

So I think one out of the 3 Good "Modifiers" is still out there in the carb business.
John Reed, RIP, was one of the 3 modifiers that made an improvement.
Braswell Carbs was another modifier that made an improvement, Braswell is still out there.
Brad Urban, RIP, was the third modifier.

Tom V.

** Quick Fuel was not in the testing, because Marvin & Marty had not left Holley to start QuickFuel Carbs, that happened later on.
Believe Marvin and another gentleman were the Dyno Operators for the testing. That was a long time ago.

[4zpeed]

Originally Posted by amcmike

I didn't even know we could rate posts till you said that... added a 5 star (well deserved IMO), but looks like it didn't move the needle much. Just forget the haters. They can move on.

The info. is extremely valuable. Nice to have an expert that knows what they're talking about. Not just the hardware, but tuning as well. And maybe, (just maybe) it'll prevent a carb or 2 from getting hacked up by some "expert" that "thinks" they know how to make the carb "work better" on the engine.

Actually that might be a good topic... what NOT to do to a Holley. I'm sure you've seen/heard some wild stuff. Like drilling out jets to increase flow, removing the inlet filter, or removing the check ball on the secondary diaphragm.

Truth ! Every bit !

Everyone needs to learn.

I like to hear it from the side of the horse that talks...


Thanks Tom,
....
Frank

[Tom Vaught]

A simple calculation I use all the time when playing with Holleys and Boosted Engine Systems.

The ASSUMED CONSTANTS:

M (dot over the M) = 1
R specific = 1545.348
T1 = 116 degrees F (assumed Underhood Temp)
Ta = 575.67
Z = 1
Pa = 14.6959494
P1 = 0
MW air = 28.9644
Q = 14.51358717 Cubic Feet of Air per Pound of Air

1 divided by 14.51358717 = 0.068900954 Lbs of Air Mass per Cubic Foot of Air.

If you lower the Temperature T1 to 80 degrees F (vs the previous 116 degrees F)
80 degrees F now being AMBIENT Air Temp vs Underhood Air Temp you get:

Q= 13.60596798 Cubic Feet of Air per Pound of Air

1 divided by 13.60596798 = 0.07349716 Lbs of Air Mass per Cubic Foot of Air.

So Temperature of the air entering the carb does make a difference in the Holley Fuel Calibration.

Tom V.

[Tom Vaught]

So now I will show you the Formula and how I got the answer above.

Top part of the formula:

1.0 times (1545.348 divided by 28.9644) times (80 plus 459.67) times 1.0

So we moved the 28.9644 to the bottom part of the formula and we get:

1.0 times 1545.348 times 539.67 times 1.0 = 833977.9552

divided by

28.96443 times 144 times 14.6959494 = 61295.01087

or

833977.9552 divided by 61295.01087 = 13.60596798 cubic feet for 1 pound of air mass.

You can do that for any air temp, air pressure, etc to get the cubic feet of air for 1 pound of air.

Same deal you can get the air mass per cubic foot by dividing 1 by the cubic feet above or 0.07349716 pounds per cubic foot


Tom V.

[Tom Vaught]

I am going today to talk about the Holley Carb Fuel Bowl "Fuel Level" and what effect that "Fuel Level" has on the carburetor operation. This info would also apply to other carbs in many cases.

The parts in the Fuel Bowl are:

1) The Fuel Bowl Casting
2) The Fuel Bowl Inlet Port
3) The Fuel Bowl Filter (if it has a provision to contain one)
4) The Fuel Bowl Needle and Seat
5) The Fuel Bowl Needle and Seat Adjusting Nut
6) The Fuel Bowl Needle and Seat Adjusting Nut Lock Screw
7) The Fuel Bowl Float
8) The Fuel Bowl Inlet Nut and sealing Washer

Next we move on to the actual operation, What happens when fuel enters the Fuel Bowl

a) Fuel from the Fuel pump passes thru the Sintered Bronze Fuel Filter (if one is installed) and flows to the inlet port on the Needle and Seat.

b) Fuel passes thru the Needle and Seat and flows into the Fuel Bowl raising the fuel level in the bowl until the Float begins to restrict flow to the bowl. If the Fuel Bowl is not supplying fuel to the carb circuits then the Needle shuts off the fuel flow by contacting the Seat.

So what happens if you have too high of a fuel level in the fuel bowl?

The Carb Metering Block Main Well Passage and the Fuel Bowl are kind of like the two "Legs" on a U-Tube Manometer (See Pic Attached).

If the Fuel Level is too high, The Main Well 'Start-Up Point' will happen sooner because there is less "Pull-Over" Signal required by the Carb Booster to cause fuel to flow.
This causes "Nozzle Drip" in the carb under Idle Conditions.

It can also cause Fuel to pass thru the Carb Vent Passage and flow into the Carb Main Body if a quick Brake Stop or Left/Right action of the steering takes place by the Driver.
High Fuel Level is not a good thing. This can also be caused by excessive Fuel pressure overcoming the Float force on the Needle and Seat.

If you have "Nozzle Drip" or fuel passing thru the Vent system, this can cause the engine operation to diminish or the engine to stall.

There are more reasons why a High Fuel Level is bad but I will not go into those today.

If the Fuel Level is too low, The Main Well 'Start-Up Point' will happen later because there is more "Pull-Over" Signal required by the Carb Booster to cause fuel to flow.
This causes "Flat Spots" in the Carb Function Curve under drive conditions and can cause Hard Starting on initial Fireup as the Main Well also feeds the Idle Feed Restriction/Idle Circuit of the Carburetor.

The fuel level would have to be fairly low on the Holley Carb to have the Fuel run away from the Main Jets on turns and very unlikely on the Main Jets in the Front Bowl on acceleration as the fuel rushes towards the main jets.

There could be an issue on the Secondary Jets, even with the fuel level set correctly, on quick accelerating vehicles. Jet Extensions, "Notched Floats", and "Trimmed Fuel Vent Whistles" help out with that mode of operation (in the Fuel Bowl).

Last, but not least for today, Installing a Needle and Seat of the wrong size can either cause a loss in performance at higher rpm or a "Raised Fuel Level" in the Fuel Bowl which will cause the issues mentioned above.

Most "Simple Parts" can cause "Big Issues" in Carb Performance if improperly selected or installed.

Tom V.

[Tom Vaught]

Today I am going to post up a bit of data from Mike Urich's (my Holley Boss) early Holley books. You don't even have to buy the book, Lol!

The Info will be posted in sets of data vs inlet Needle and Seat orifice size and fuel pressure.

a) Diameter of Needle/Seat Orifice = .082"
Needle and Seat uses "Holes" for fuel flow
Fuel Flow @ 2 psi = 106 Lbs/Hr of fuel
Fuel Flow @ 4 psi = 153 Lbs/Hr of fuel
Fuel Flow @ 6 psi = 204 Lbs/Hr of fuel

b) Diameter of Needle/Seat Orifice = .097"
Needle and Seat uses "Holes" for fuel flow
Fuel Flow @ 2 psi = 121 Lbs/Hr of fuel
Fuel Flow @ 4 psi = 174 Lbs/Hr of fuel
Fuel Flow @ 6 psi = 225 Lbs/Hr of fuel

c) Diameter of Needle/Seat Orifice = .101"
Needle and Seat uses "Holes" for fuel flow
Fuel Flow @ 2 psi = 138 Lbs/Hr of fuel
Fuel Flow @ 4 psi = 194 Lbs/Hr of fuel
Fuel Flow @ 6 psi = 254 Lbs/Hr of fuel

d) Diameter of Needle/Seat Orifice = .110"
Needle and Seat uses "Holes" for fuel flow
Fuel Flow @ 2 psi = 153 Lbs/Hr of fuel
Fuel Flow @ 4 psi = 230 Lbs/Hr of fuel
Fuel Flow @ 6 psi = 275 Lbs/Hr of fuel

e) Diameter of Needle/Seat Orifice = .110"
Needle and Seat uses "Windows" for fuel flow
Fuel Flow @ 2 psi = 160 Lbs/Hr of fuel
Fuel Flow @ 4 psi = 232 Lbs/Hr of fuel
Fuel Flow @ 6 psi = 295 Lbs/Hr of fuel

f) Diameter of Needle/Seat Orifice = .120"
Needle and Seat uses "Windows" for fuel flow
Fuel Flow @ 2 psi = 167 Lbs/Hr of fuel
Fuel Flow @ 4 psi = 236 Lbs/Hr of fuel
Fuel Flow @ 6 psi = 305 Lbs/Hr of fuel

A couple of things you will notice from the information:

1) The Needle and Seat Orifice Size did not "Bump Up" the actual flow volume in Lbs/Hr
very much for each .010" increase in diameter.

2) The actual flow volume in Lbs/Hr DID increase quite a bit for each 2 PSI increase in fuel pressure.

So you might think if I need for Fuel Flow per Bowl I need to jack the fuel pressure up to 8 psi or 10 psi. WRONG.

This is where the BOOST GUYS hardware can help you with fuel flow capability.

They have Dual Needle and Seat Bowls that you can use on your Dominator Carb to basically double the fuel flow to the jets and the engine. Not inexpensive but they work well for bigger engines with larger Dominator Carbs.

Food for thought. I have attached a couple of pictures for you.

The KEY IS, NOW you can still run the Holley recommended 6 psi fuel pressure to the bowl and main wells but can supply twice the flow to the bowl without screwing of the fuel pressure vs fuel level equation inside the bowl.

Tom V.

[Tom Vaught]

One other comment:

The First Dual Needle & Seat Holley Carb Bowls I saw was many years ago at Norwalk Raceway Park at a IHRA Pro Stock race.
The Bowls were on a 700+ cid Pro Stock Engine (back in the days when IHRA ran large engines vs the NHRA 500 cid engines.)

So the technology was first used on NA engines, not Boosted Engines, that came later.

Tom V.

[Tom Vaught]

Sorry for not posting lately on the Holley Carb thread.
I am getting a new Garage Door 18 foot by 8 foot to replace the HEAVY WOOD door that decided to fail after 50 years of service. "Piece of junk"/ NOT!!!!!!!

So I had to clean the garage so that the workers could remove all of the old garage door stuff and not damage the GTO (That means I had to figure out how to get it out of the garage the day of the Garage Door swap.)

So only one more step now. Garage Door Swap Day.

So I have time to post while they are building the door.

First topic for today is a little bit of carb history vs today's modern EFI
systems.

As the Emissions and F.E. Standards got tougher, Holley and other carb manufacturers had to get involved in designing Emissions Carbs to help the OEMs meet the standards.

One way that they did that was by using a "Feedback" system on the Carburetor to meet the NOx requirements. Feedback systems are also called "Closed Loop" systems.

With a "Closed Loop" system, the amount of fuel and air passing thru the engine is controlled by ENGINE DEMAND as well as air flow thru the carb venturis.
The "Closed Loop" systems were able to "balance" the components of the exhaust to allow a "Three Way Catalyst" to be used. To find out where they where in this "balance" they used a NEW TECHNOLOGY involving a Bosch Lambda Sensor (a Oxygen Sensor).

Now Holley had been using a Bosch PRO Lambda system to tune Holley Carb Performance Calibrations several years before the Emissions and F.E. Standards were in place. So the best investment you can make if you are tuning carbs for a living/FUN or Racing is to invest in a Oxygen Sensor Air/Fuel Ratio (Lambda) system.

The next "TIP" or comment is to talk about the Holley "Mile Dial" and "Quarter Mile" carb systems/Bowls that allowed you to change jetting on the Fly while driving down the road.

Davis Vizard, a well known Dyno Tuner, used his Quarter Mile Doal System to change jetting on the carb on the dyno without removing the fuel bowls. You could get about a 5 jet size change with the system.

That being said, most of the systems are long gone now.

A Road Race Guy (Silver State ON ROAD) racer type guy used a pair of the systems to tune a dual quad system for 150 mph dashes across the desert during the desert cool nights. Basically a NASCAR type application with no turns involved. Point A to Point B type racing. Today we have the Holley and Edelbrock Throttle Body/ Port Injection systems doing the same thing only better and used by the average Pontiac Guy on the street.

So the Holley parts have been there for a long time just much more 'sophisticated' now vs the old Quarter Mile Dial systems.

Tom V.

[Tom Vaught]

Been a while since I posted on Holley Carbs and decided to post today about the need for a Secondary Throttle Shaft/ Throttle Blade Adjustment capability.

In the old days we would remove the stock Slotted Head Screw (slot on the bottom surface of the baseplate) and flip the screw over so now the Slotted Head Screw was pointed upward.

You usually had to pean the thread slightly to make the screw stay in one spot on the adjustment.

You could also use a stainless Allen Hex Head screw slightly longer and forget about the very small flat blade screwdriver required with the stock stuff.

Today that is a whole different deal.

Now on EBAY you can buy am adjustable secondary pump cam mounting part that has the adjustment screw built into the assy. I have included a Picture below.

The POINT OF THIS POST is to tell people get the Primary Blade to Transfer Slot adjusted and then never touch the Primary adjustment screw from that point if you need to change the idle rpm of the engine. USE THE ADJUSTABLE SECONDARY SCREW TO SET THE IDLE.

Tom V.

ps Holley wants $50 for their part, RPM/QFT wants around $15.00