How to Transform Your Holley 3310 into a More Aggressive-Looking 4150

By Jeff Smith – Photography by the Author

If we had to pick one Holley carburetor to represent the entire history of Holley carburetors, we would choose the 3310. It is the ubiquitous carburetor. Originally created as a 780-cfm vacuum secondary, four-barrel, original-equipment carburetor on many GM big-block engines, this carb has evolved into the go-to standard for street performance.

This is the classic 0-3310C Holley 750-cfm vacuum secondary carburetor. This is the basic version with a mechanical choke. Note this is a 4160 version carburetor with no secondary metering block—which we’re going to remedy right now.

This carburetor became so in demand that Holley quickly began selling this carburetor first as a 4150 style, which includes a secondary metering block. Over the years, to attract an even broader clientele, the 0-3310 was converted to the 4160 version, meaning the secondary metering block was replaced with a metering plate but still with the same metering characteristics. Along the way, its rating slipped slightly to 750 cfm. There were a few other changes, but the demand continued.

Today, we’re looking at a current version 0-3310-13, which Holley calls the 0-3310-C or the classic version in the traditional gold dichromate finish. Buy one off the shelf and it comes as a dual inlet carb with a mechanical choke, two-hole idle circuit, straight-leg boosters, and no metering block. Or maybe you have one that’s been on your small-block for years and it’s time for a mild upgrade. We have just the plan.

This is Holley’s 34-13 conversion kit that includes the metering block, jets, block and bowl gaskets, as well as four longer bowl screws and gaskets. This is everything you will need to do the conversion.

The only real issue with the current 4160-style version 0-3310 is the rear metering plate. A couple of engine upgrades may require more secondary fuel, but the hassle is that the secondary metering plate uses fixed jets. The amount of fuel flowed by the secondary is determined by a pair of drilled orifices in the secondary plate. To change the jetting requires replacing the plate with one with a larger jet size. This is a hassle and quite expensive. But there is a simple solution.

Holley offers a conversion kit that replaces the 4160-style metering plate with a 4150 metering block that allows the secondary jets to be easily tuned (PN 34-13). This kit and all the other parts mentioned in this story are available through Speedway Motors. The kit includes a metering block, secondary jets, all the necessary gaskets, and longer screws to retain the secondary bowl. The conversion is very easy and can be accomplished in a few minutes. We’ll run through this process for you and offer a few hints and tuning tricks along the way.

We performed our conversion on the work bench mainly because it made the photography easier. You could do this swap with the carb on the engine, but it would be easier on the bench. If you remove the carb from the engine, always lay a towel or shop rag over the intake so no debris or small birds fall into the intake manifold. We began the disassembly by draining the fuel out of the secondary bowl after removing a lower bowl screw. Then we removed the other three screws and pried the bowl off. Don’t worry if the gasket tears as the kit includes new gaskets.

One additional note is that if the carburetor is already on the car, the current dual-inlet fuel line will not bolt back on because the carburetor is now slightly longer, placing a greater distance between the dual inlet bowls. This will require a new fuel line. You can lengthen your current line, make a new one out of some Earl’s fittings, or just buy one of several fuel lines from Earl’s or other vendors.

With the secondary bowl removed, we can see that secondary metering plate is attached with six 5/32-inch clutch head screws. This will require a special clutch-head screwdriver or bit set that’s available through the Internet. In a pinch, you can try grinding a straight screwdriver blade down to fit inside the recess of these screws.

It’s also worth noting that this same conversion can also be accomplished on the shiny version 0-3310S carbs as well as Holley also offers a similar metering block kit for that version carb. There’s also a kit to convert the popular 600-cfm 0-1850 Holley over to a metering block The 600-cfm kits do not come with jets since they cover several different versions of 600-cfm 4160 Holleys. So those kits will require ordering separate secondary jets. The kit PNs are listed in the accompanying chart.

With the secondary bowl removed, we can see that secondary metering plate is attached with six 5/32-inch clutch head screws. This will require a special clutch-head screwdriver or bit set that’s available through the Internet. In a pinch, you can try grinding a straight screwdriver blade down to fit inside the recess of these screws.

Besides this conversion, there are several other easy how-tos that can upgrade this basic carburetor. Holley offers an electric choke conversion as well as a Quick Change kit that slows easy changes to the vacuum Diaphragm spring. These are all bolt-on kits that are easy to install and will take your basic 0-3310 to the next level. Plus, there are all sorts of simple carburetor tuning tricks that you can do to fine-tune your carburetor to your particular engine.

But we’re getting ahead of the game. For the moment, let’s run through how to convert your 4160-style Holley 0-3310 to a much more competition-looking carburetor that will make it much easier to make a simple jet change.

Fit the four longer bowl screws with their new nylon gaskets and then install the fuel bowl over the metering block and lightly start all four screws before tightening. Just cinch the screws in place—do not apply excessive force, as this tends the distort the carb main body and can cause driveability problems due to vacuum leaks.

Remember to install the nylon gaskets on the new longer bowl screws to prevent leaks.
The bowl gasket fits over the pins on the metering block. The gasket is designed to also be used with double-pumper carburetors so there is a hole for the acceleration discharge tube that in this case is not used.
Make sure the metering block gasket fits properly over the two pins. This prevents the gasket from being installed incorrectly.
We installed the two number 75 jets in the metering block. Note that the new secondary metering block is not machined for a power valve, mainly since it is not necessary. The 75 jetting should be very close jetting for mildest small- and big-block applications.
This detail view of the metering plate shows a number stamped in the plate that corresponds with the equivalent jet size. The “21” stamped in this plate is equal to a pair of 75 Holley jets, which are included with the kit.

This is Holley’s 34-13 conversion kit that includes the metering block, jets, block and bowl gaskets, as well as four longer bowl screws and gaskets. This is everything you will need to do the conversion.

Our converted 0-3310 will now require a longer fuel line since the distance between the bowls has not increased. Here we’ve installed an Earl’s Ano-Tuff fuel line but there are multiple options available to choose from. This carb is now ready for the street!

Secondary Metering Plate Jet Sizes

Metering Plate

Number

Equivalent

Jet Size

8 or 9 64
22 or 3 65
6, 37, 39 69
12 73
21 or 54 75
27 79

Parts List

Description PN
Holley metering block conversion kit for 0-3310, standard 34-13
Holley metering block conversion kit for 0-3310, shiny 34-13S
Holley metering block conversion kit for 0-1850, standard 34-6
Holley metering block conversion kit for 0-1850, shiny 34-6S
Earl’s -6 Ano-Tuff black dual inlet fuel line for 4150 Holley AT104195ERL
Earl’s -6 dual inlet fuel line, braided steel 101175ERL

 

Sources
Earl’s
(866) 464-6553
www.holley.com/brands/earls/

Holley
(866) 464-6553
www.holley.com

Speedway Motors
(800) 979-0122
www.speedwaymotors.com

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