[Tom Vaught]

Going to talk a bit more about Holley carbs and what happens when you change the AIR TEMP (density) going thru the carb.

Say you have a Holley 850 CFM #4781 Holley Double Pumper mounted on your engine under the Hood of your Trans Am 455 cid engine.

You measure the air temp going into the carb and it is 112 degrees F air temp.

So if we plug that into a spreadsheet I have it says that the Air Mass (in Pounds per Minute) is 58.873 going thru the carb.

So then you install the hood off of a Formula vehicle (the one with the forward facing scoops that can be opened up. Basically now getting fresh air from the front of the vehicle. Air temp is 77 degrees outside. With a sealed to carb system, the air mass going thru the carb/ engine is now 62.822 (in Pounds per Minute).

If you opened up the Trans Am scoop (which is not quite as efficient as the Formula scoops) you would get a bit less air mass with a similar sealed system.

But comparing 62.822 lbs/min vs 58.873 lbs/min = 3.949 difference times .80 volumetric efficiency = 3.150 difference.

So for easy math 3 lbs/min difference on average.

Rough rule of thumb is 1 lb/min air mass change will get you from 9.5 to 10.5 HP change. So call it 10 horsepower.

SO A PROPER COLD AIR INDUCTION SYSTEM COULD GET YOU UP TO 30 MORE HP VS CONSUMING UNDERHOOD AIR ON YOUR VEHICLE.

So the Ram Air probably did not do much but the difference in actual air temp in the two examples shows the air density change/ AIR MASS Change to be worth 30 HP.
(Ram Air really only works once you get above 150 MPH.)

Tom V.

You might need a 1 jet change to the carb in all 4 spots to allow for that air mass increase.

[Tom Vaught]

It has been almost a month since I posted last on the Holley Carburetor Info and Tips thread. So today I am going to talk about tyhe Holley List Number #3310 780 cfm carb and how to build one up so you can "JET ONE UP" easily.

1) There are still a LOT of the old Holley 780 Vacuum Secondary List 3310-1, 3310-2, 3310-3 4 barrel carbs out there at the swap meets. There are also a lot of the Chevrolet OEM versions of the same carb at swap meets. They were used on the 396 cid Chevy Engines and will have a Chevy part number along with the Holley #3310 List Number.

The #3310-1, #3310-2 and #3310-3 carbs can still be found at swap meets cheap as Holley made a million of them over the years and are still making a version of the same carb. Assume that you can buy the carb for as little as $15 - $25 for one with all of the pieces. Try to buy TWO #3310 carbs and use one for pieces to build a really good 4 bbl carb. You need at least ONE good Mainbody, at least TWO good Primary Metering Blocks, One good Baseplate and Shafts, and two good Race Bowls for the carb we will assemble.

On the Secondary side of the carb you will see that most #3310 carbs will have a Metering Block on the Primary and a Metering Plate on the Secondary.
(#3310-1 Carbs used TWO Metering Blocks). We are going to try to build a carb like a 3310-1 carb with the TWO Metering Blocks.

So if you skip ahead you went to the swap meets and found the ONE good Mainbody, at least TWO good Primary Metering Blocks, One good Baseplate and Shafts, and two good Race Bowls for the carb we will assemble.

It is very easy once you have the carbs and you remove the rear fuel bowl to determine that you need a "Clutch Tip" screw driver bit to go on your interchangeable bit screwdriver to take the Rear Metering Plate off the carb. So make sure that you have one of those somewhere in your tool box.

So you take the Bowl off and you see that Metering Plate you removed had a #24 Stamp on the plate. What this means is that you need two #72 Metering Jets on the second Primary Metering Block you are going to install on the secondary side.
When you do that you will be able to change jets in all 4 spots without drilling parts (Metering Plates). This is what this post is all about. Building a cheap 780 cfm carb like the #3310-1 carb that had two metering blocks.

In another post I will post up the equivalent Jets for each Metering Plate that Holley offered on their Secondary side of the 3310 type carbs. Time for Lunch

Tom V.

[ta man]

Thanks Tom I had one of those carbs show up on a parts car..just need to find another or...what other metering blocks will work?

[Tom Vaught]

The 3310-1 or -2 metering Blocks used to be available from Holley as part of a Rear Metering Block Kit. Kit Part Number was 34-13 and it came with the gaskets and the longer Bowl Screws needed with a Metering Block. A Metering Plate fits inside the Rear Bowl so they use the shorter bowl screws.

ALL of the Metering Plates used the same Prefix which is 134.

So a Metering Plate stamped 134-3 would have a "-3" would have a orifice with the same flow as a Number #56 Jet.

So for the complete list I will just type "-3 is #56 Jet" or "-4 is a #59 Jet"

"-3 is #56 Jet"
"-4 is #59 Jet"
"-5 is #63 Jet"
"-6 is #69 Jet"
"-7 is #53 Jet"
"-8 is #64 Jet"
"-9 is #64 Jet"
"-10 is #65 Jet"
"-11 is #72 Jet"
"-12 is #73 Jet"
"-13 is #63 Jet"
"-14 is #85 Jet"
"-15 is #82 Jet"
"-16 is #64 Jet"
"-17 is #69 Jet"
"-18 is #63 Jet"
"-19 is #69 Jet"
"-20 is #69 Jet"
"-21 is #75 Jet"
"-22 is #65 Jet"
"-23 is #64 Jet"
"-24 is #72 Jet"
"-25 is #77 Jet"
"-26 is #79 Jet"
"-27 is #79 Jet"
"-28 is #65 Jet"
"-29 is #75 Jet"
"-30 is #64 Jet"
"-31 is #74 Jet"
"-32 is #59 Jet"
"-33 is #64 Jet"
"-34 is #53 Jet"
"-35 is #69 Jet"
"-36 is #64 Jet"
"-37 is #69 Jet"
"-38 is #71 Jet"
"-39 is #69 Jet"
"-40 is #59 Jet"
"-41 is #69 Jet"
"-42 is #94 Jet"
"-43 is #71 Jet"
"-44 is #74 Jet"
"-45 is #79 Jet"
"-46 is #75 Jet"
"-47 is #78 Jet"
"-50 is #79 Jet"
"-53 is #65 Jet"
"-54 is #82 Jet"
"-55 is #78 Jet"

There is no "-48", "-49", "-51", "-52", or "-56" Metering Plate.

So when you find your #3310 Metering Block/Carb you will know what Jets to put into it on the rear side to have a carb with the same designed in jetting at the factory metering Plate carb. Except now you can jet up or down to dial it in further.

Typically the Holley Calibration is with-in two Jet #s of what the engine wants.

Have a great evening

Tom V.

ps Copy and Paste the info from this post onto a Word File or Excel File and put it in your Carb "toolbox"

[beargfr]

I just found (actually was told about) this thread and have read the whole thing. Wow - what a trove of information. Thanks Tom!

I'm "right now" in the middle of trying to get an AED "850" HO Annular dialed in on my 69 GTO. It's my first experience with a Holley platform so my learning curve is steep. It's on a Northwind single plane on a 461 stroked 400, solid roller (251/257 @ .050, 110 LSA, 106 ICL, .620 net lift at the valves after adjusting for lash), 10.3:1, 72 cc Edelbrock round port heads, 2.190/1.77 valves, TH 400 w/3100 rpm converter, 3.50 gears, 27.7" tall Nitto NT555-R's. I just got the engine back together and running recently after being down for "awhile" (long story) and made the aforementioned changes as part of that. Previously it had less cam (236/242 @ .050 - .010 less lift) less compression (10:1) running a real 455 SD QJet on a Torker 1 (only intake I had at the time that would cover the ports in the heads).

I have an AEM X-series digital A/F meter in it. Out of the box it was really rich everywhere, especially at part throttle light cruise - A/F in the 9's-10's all the time, and it was actually a little leaner at WOT but not by much. The carb out of the box came with 81/91 primary/secondary jetting, 4.5 power valve on the primary side only (secondary has a plug), .035 pump nozzles, .070 idle air bleeds, .031 high speed bleeds, and .035 idle feed restrictions in what thanks to your thread I now know to be the less than ideal "high" location on the metering blocks. I struggled with it for a good while before finally making some progress with it. Already I've changed the oil more than once due to it smelling like fuel.

I've been able to do a lot to get cruise mixtures to where I think they should be - 13's-14's even occasionally low 15's - that AEM meter reacts really quickly, and one thing that has been a surprised is how widely the mixture varies even under what I'd thought would be steady state.

What I've changed so far:
Idle air bleeds: .084
Jets 76/86
Idle feed restrictions .031
Idle RPM 950 in gear , mixture screws 1 3/4 turns out - gives me a meter reading in the 13's-14's. and 10" of idle vacuum. It's amazing to see how large an effect even 100 rpm of idle has on vacuum and also mixture reading. It's dramatic.
WOT is still fat, 11.9:1 - thinking I might go down one more number on the jets in both ends.
Plugs are looking decent - medium brown coloration now (93 octane unleaded), whereas before they were sooty black (duh)

I've also got Dave Vizard's Holley book and have been studying that.

Should I "move" the IFR to the lower location you think? Do the changes I've made so far make sense?

Thanks,

Bear

[Tom Vaught]

Move the IFR to the lower location so that you will be calibrating liquid fuel vs fuel and air bleed air at the "high" location you are now. That deal always screws things on the idle up.

I helped Cliff Ruggels with his 4781 850 carb years ago. It was always a bit rich.
Cliff Ruggles had a great idle calibration with no more than a .074" air bleed required.

KRE said (according to Cliff) Don't touch it it is perfect on the dyno. That was years ago but the info is still valid.

A .084 air bleed says things on that idle circuit are not right.
AED has always had some "different" calibrations with their carbs.

Send me a PM and I will give you some of the 850 factory carb specs that might work better.

Stock jetting on a 850 carb with downleg boosters is #80 jets. Annular can be about 2 sizes smaller.
Annular Boosters might be able to run a #78 jet because of the stronger signal from the boosters.

When you PM me we can talk about where the throttle blades need to be on the carb and if the AED carb is even machined close. I assume this is a 4 corner idle carb.

Tom V.

ps we can document what you did so far then try a few things like Holley did them and see if the carb matches more closely to Cliff's calibration.

[Tom Vaught]

Who would have an interest in Holley carbs produced as OEM carbs for Chevrolet but you want to use one of them on a Pontiac Vehicle?

I have about 60 Holley Carb List Numbers (for the Chevy Applications).
This info includes the Holley List Number, the Chevy Engine Size, the Chevy Body Style, the Chevy Part Number for the carb (same one as stamped on the Air Horn of their carbs), Primary Metering Block Number, Secondary Metering Plate or Block Number, and finally the Carb Throttle Base and the part number stamped on it.

If you have some Carbs/ Numbers, Post them up, and I will match your numbers to the application and post the specific info for everyone for that carb.

Tom V.

[Skip Fix]

I remember about 1970 picking up an 812cfm DP that was in a GM box my speed shop had bought a bunch of. Not sure what the original application was. Worked well on my 409 when it was single quad.

[Tom Vaught]

May have been the Special Corvette Carb for the 1970 454 465 HP List Number #4493.

Was it a Double Pumper Carb, Skip, or a Vacuum Secondary Carb?

Tom V.

[Skip Fix]

DP Tom also had a weird choke mechanism on it not the normal ones I've seen on Holleys.

[Tom Vaught]

That pretty much locks it in that it was the 465 HP Factory Holley Double Pumper for the engine, Skip.

So the rest of the info for you is:

Holley List #4493
454 Cubic Inch Engine
1970 Corvette
Chevrolet Number #3967487
Primary Metering Block #6203
Secondary Metering Block #6207
Throttle Plate Base Number #4485

Skip, this would have been the same basic carb as a later #4780 Double Pumper Aftermarket Carb. Also about 800 cfm.

Tom V.

[Tom Vaught]

I was looking at some old files and came across this link to a Holley Specifications Manual.

What is unique about this manual is that it gives actual Photos of the different Holley carb Airhorns and where the "identifiers" are for the different model carbs are like the 2300, 4150, and 4160 Carbs. For the 4011 carbs, 4165 carbs, and the 4175 carbs. And finally the location on the 4500 Dominator Carbs for the model #.

All of that info is good but the part of the document I like is the specific settings for things like:

List Number and settings like: Dry Float Setting, Choke Index, Dashpot, Pump Cam Position, Vent Valve Setting, and the Choke qualifying setting. FOR EACH CARB.

HERE IS THE LINK TO THE INFO: https://documents.holley.com/199r10015-1rev.pdf

I have not posted on the Holley Carb thread in a while but felt this needed to be added to the sticky.

Tom V.

[Formula jg]

Tom,
Just because there hasn't been any posts on this thread for a little while doesn't mean they're not being read.

I thank you for keeping the Holley information flowing here and more importantly helping keep the carb culture alive.

Cheers

[Tom Vaught]

I posted some info, years ago, up on a Internet Carb Board that primarily dealt with Racing Dominator Carbs.

This was back in 2010. The Web Guy gave me credit for the info. So I will pass the info on to you.

Info is from Tom Vaught, a former Holley employee.


1) Why the Holley Hex Nut above the the Float Bowl has 6 sides (vs say 8 sides):

The thread used on the needle and seat that screws into the top of the float bowl is a 3/8-32 thread. There are 32 threads per inch cut on the needle and seat where it goes into the bowl.
One full turn of the Hex Nut will move the needle and seat 1/32” or .03125”
or for easy math about .030” upward or downward.

2) Why the actual float moves vs the tip of the needle (away from the seat):

The float has a 6 to 1 multiplication ratio so you turn the needle and seat hex nut one full turn downward, the float movement will be .03126 X 6 or .1875” lower in the float bowl and the average fuel level in the bowl will be for easy math .180” lower. Two “Flats on the Hex nut works out to about a 1/16” of fuel level change in the float bowl. If you keep accurate records of your float level position you can track the air/fuel ratio change (with an accurate air/fuel meter and get the fuel bowl fuel level vs the mail well fuel level dialed right in for your intake manifold/ carburetor/ engine installation angle dialed right in for best fuel control.

3) Why the fuel level rises in the bowl, (above the Holley Calibration Level), when a higher fuel pressure (vs the Holley fuel pressure spec of 6 psi) is used:

When the needle and seat (.110” size) is used with a factory float bowl and at the Holley fuel pressure calibration point (6 psi), the average float level height will be close to the “design fuel level” in the bowl and and the carburetor will will meter fuel properly. In some of the old Holley Books they used to show an external gage mounted on the fuel bowl to check fuel level before the “Sight Plug” type bowls were designed. If you add extra fuel pressure to the fuel line going to the bowl the needle and seat will have a higher pressure acting on the tip of the needle and seat. A small change here in force acting on the tip of the needle vs a fixed float buoyancyforce X a 6 to 1 float ratio mentioned above means that the FUEL LEVEL IN THE BOWL WILL RISE TO A NEW AVERAGE LEVEL WITH INCREASED FUEL PRESSURE.

4) Why the fuel level rises in the bowl, (above the Holley Calibration Level), when a larger needle and seat is used (vs the Holley .110 needle and seat).

In the previous paragraph 3), the fuel level went up because the pressure on the float was higher due to the fuel pressure. The other way the level can go up is by using a larger area needle and seat which also imparts more force against the float, (raising the average fuel level.
A Holley 6-504 part Number is Holley's standard .110” Viton Needle and seat assembly
A 6-505 needle and seat will flow about 170-180 lbs of fuel per hour at 7 psi (depending on the
specific gravity of the fuel used). 175 x 2 = 350 lbs of fuel per hour. About 630 horsepower if
assuming a .55 lbs/horsepower/hr. Using the larger needles and seats naturally will move more
fuel BUT flue level changes in the bowl will have to be monitored for each combination vs
expected air/fuel ratio and drivability.

5) Why “Float Drop” is important:
If you have the wrong float drop, the float can “hang” against the needle as it rides on the “hump” on the float level. There are two needle and seat lower needle dimensions. One needle has a 2 cm lower diameter and the other one has a 4 cm diameter. Naturally the 4 cm diameter needle and seat will not “hang” as easily as the “footprint” (diameter) is twice as large. If the float “hangs” you will have open flow into the bowl with no fuel control and flooding, fuel coming out of the vents, and potential “hydra-locking” of the engine. As second issue with the wrong float settings is that the fuel level in the bowl could be too low and uncover the power valve on acceleration. Special power Valves can help eliminate this issue.

6) Why Floats collapse after a Carburetor Fire:

If you have a carburetor backfire, and the carburetor is burning inside the venturis, the main-body gets hot quickly. This heat transfers to the air in the carburetor heating it and the also to the parts around the air. The brass floats have air inside of them when they were made. The air in the float gets hot, expands, and trying to get out of the float. Many times there are very small places where the air can escape but fuel cannot get into the floats. As soon as the engine is restarted, the cold fuel enters the bowl, the float is still hot. The float cools rapidly vs the lost air inside the float. Because the air pressure outside is now higher vs the inside of the float the float collapses (just like it would under boost). Now you have a big problem. The black Nitrophyl floats do not suffer this problem therefore as we know are a better component to use in a boosted carburetor. At least now you can explain to your buddy why his float looks like Chit when he was not running any boost through the carb, LOL!

7) What the “Standard” Brass Float should weight vs what the Black Nitrophyl Float weighs:

A Brass float weighs around 15 grams. (An average paper clip weighs 3 grams). The black nitrophyl float weighs about 11 grams. When you cut notches in the black float to allow for jet extensions, (or if you buy a black float with the notches already there), you should check the weight of the float on a gram scale to see if it is close to the right factory weight. You never know how much epoxy the guy used sealing the float, how deep he made the cuts, etc. Some floats for the road race guys and NASCAR guys are heavily modified. If the float is too light, (less than 11 grams stock, or if you want to make the float the same weight as the brass float you can add extra lead shot to get up to the brass float weight of 15 grams.

Cool Adding weight to a black float:
You drill a hole in the black float, add the weight, do a trial measurement on the gram scale, and when you are close you add the light coating of epoxy to seal the whole deal up. I am not a big fan of the making the black float weight the same as the brass float as the black float dimensions are different vs the brass float. The brass float has a longer arm therefore more force on the needle and seat vs the float weight.

9) Lean Acceleration caused by an improper float level setting:

As was mentioned in 5), if the float level drops too low, the “head” that the fuel has to overcome in the main-well gets higher and the engine calibration goes lean. If the fuel level is too high, the “head” that the fuel has to overcome in the main-well, will be much less and the engine runs rich. There is a “sweet spot” that was designed into the carburetor fuel calibration over many years of testing vs the parts used and random “experimenting” will typically cause issues over time. High pressure boosting is adding another level of knowledge to this carburetor database of proper settings.

10) Why Bowl Vent Clearance is important:

The vent whistle at the top of the metering block was added to prevent fuel slosh out of the carburetor bowl vents. A Rivet typically holes it in place. There may be a slight leakage around the vent but typically it is there for fuel control in the bowl. Trimming the vent is commonly done. You do not want the fuel to slam against the back wall of the carburetor under acceleration, climb the back wall, hit the roof of the bowl, move forward, and then enter the vent whistle. A whistle about 1.25' long typically works well. I trim the opening with an exacto knife to allow more area through the vent whistle too.


11) “Sight Plugs” Why they are different Front Bowl to Rear Bowl and why some people have carburetor problems when swapping out Holley Bowls for after-market fuel bowls:

Few Holley bowls today do not have a “Sight Plug” but the location of the sight plug can be in several different locations. Primary bowls will always have a higher sight plug location vs the secondary bowl location. The number varies all over the map. The average bowl difference will be around .220” difference with some going over .300” difference. Why is this important? Because the sight plug location sets where the “bottom of the threads” location is that everyone sets their fuel level to. As said earlier, you do not want to screw up the Holley Fuel Level Calibration Setting Point if you can help it.

12) “How to use a Primary Float Bowl on the Secondary side of a Holley carburetor:

IF you put a Primary bowl on the secondary side of a carburetor you can typically set the fuel level to the bottom of the threads deal and the LOWER the fuel level 4 FLATS.

13) Float Bowl Screws can be different:

A stock Holley Metering Block type bowl screw is 63mm long from the metal surface the screw gasket seals against to the end of the screw threads. About 2.48” long. The Metering Plate Holley screw is about 48mm long, about 1.89” long. You will notice that neither of the screws is the standard 2” long or 2.5” long hardware store bolts. At one time there were some screws out there that looked the same as the Holley typical parts but they were VERY CLOSE to the 2” and 2.5” length dimensions. You use one of these screws in your carb you are almost guaranteed that you will strip a thread in the main-body as the screw will bottom in the casting, have no where to go, and any additional tightening will pull threads.

14) Never use “Hot Rod” needles and seats parts vs the “Holley Design” needles and seats:

Above in line 13 we had a screw length issues that could cause problems. In this line we have a needle and seat thread issue that needs to be addressed. Holley needles and seats ARE as mentioned above a 3/8-32 thread. Some of the “hot rod” old style needles and seats were a bastard thread then therefore would strip out the threads in the float bowl after installation in the bowl. USE ONLY HOLLEY DESIGN TYPE PARTS.

15) Differences between Holley needles and seats:

Holley used a few needle and seat designs over the years. Initially Holley had steel needles and later offered Viton tipped needles for many applications. Holley offered several orifice sizes, with the .110” needle and seat being the most common. Holley also changed the feed strategy to the needle. The old units used drilled holes in the upper and lower chambers (typically 4 holes). The later generation parts used a “Picture Window” rectangular shaped entry hole for more flow to the carburetor bowls. Today we have the stock type needles and seats and also “Bottom Feed” type racing needles and seats.

16) Viton tipped needles and seats vs steel needles and seats:

Last but not least Viton Tipped needles and seats vs steel needles and seats. The Viton stuff seals very well unless you get metal chips stuck in the viton tip. A steel needle and seat will typically allow the trash if small enough to pass through the needle and seat to the bowl. Steel needles and seats are used on higher performance applications when using exotic fuel blends as the viton tip parts are designed for normal pump fuels and some racing fuels. Most alcohol carbs will use a steel needle and seat for two reasons: Increased orifice diameter required where the viton part is not offered and durability from the corrosive fuel. The increased fuel orifice diameter requirement can be corrected by the dual needle and seat strategy but the corrosive fuel issue is still there.

Tom Vaught

[Formula jg]

Tom, this info is invaluable for us carb die-hards.

Item #10, would you happen to have a pic of a trimmed whistle?

[Tom Vaught]

Originally Posted by Formula jg

Tom, this info is invaluable for us carb die-hards.

Item #10, would you happen to have a pic of a trimmed whistle?

I do not have access to a camera but I do have the dimensions for a Stock White Vent Whistle and the modded White Vent Whistle right in front of me.

Stock White Vent Whistle

Length overall = 2.000" (some may have a slight more or less).

Vent Whistle width is about .6000" (My sample is .605" wide where it fits into the metering block window).

Opening on the end of the whistle (top surface) is .325" from edge of whistle tip and width is .465" length of whistle is

Top to bottom dimension (where it fits into the metering block window) =.225"


Modified White Vent Whistle

Length overall = 1.600" (You can go as short as 1.25" on a pure drag car but a street/ strip car can get by with 1.6" just fine)
It has to do with how hard the fuel slams into the back wall. A car that does a lot of braking would like the longer length.

Vent Whistle width is same .6000" (My sample is .605" wide where it fits into the metering block window).

Opening on the end of the whistle is still .325" from edge of whistle tip which is now 1.600" and width is still .465" (I leave the .030" thick vertical walls on the sides of the opening).
I duplicate the stock opening design).

Top to bottom dimension (where it fits into the metering block window) =.225" as I do not modify the metering block whistle end except to drill the rivit hole in the new part if one is not drilled. A stock white whistle will have the original whistle rivit and hole already there.
The rivit is on the top edge of the metering block.

I am basically cutting .400" off the whistle to do two things:

Gain more clearance for the fuel to hit the back wall, turn, and fall back into the fuel bowl vs splash into the whistle and cause a stumble.

If I just cut .400" off the end of the whistle the vent opening would be very small (as the height does not change of the end of the vent top opening but you would lose .325" of entry area on the top side of the whistle like a stock whistle has.

So simple cut the whistle to look like the stock one in the picture attached but make it .400" shorter in length.

Tom V.

[Formula jg]

Thank you sir.
Gonna try this mod and see if it helps with my panic braking stall. Testing may have to wait untill the spring because I’m just about ready to store it for the winter.

[Tom Vaught]

Since you have identified that you do Panic Braking and get Stall, I would go with the 1.6" length initially.

Tom v.

[Formula jg]

Maybe I missed it in your write up but is this mod performed on both pri. and sec. side?

[Tom Vaught]

Secondary side for sure with Drag Race Vehicles but with your situation You need the vent whistle modification on both the front and the rear metering blocks.

Tom V.