Choosing the right carburetor is critical if you want to achieve the maximum power potential of your inline six. As such it's one of the most important decisions you'll make. Selecting the wrong carburetor, to big or to small, decreases power and driveability. An improperly sized carb may also result in hesitations and/or flat spots, poor idle quality, reduced mileage, and increased emissions. The most common mistake when building a performance motor, whether it's a V8 or an inline six, is selecting a carb which is simply to big (or over-sizing the carb). Don't fall into this trap, bigger is not better.......
The idea is to choose a carburetor that has a large enough bore and venturi to allow maximum airflow, yet one that's small enough to maintain a high-speed airflow signal through the primary venturi(s), which the carburetor needs in order to determine how much fuel is required to achieve the proper air/fuel mixture.
Lets say that again..... The idea is to choose a carburetor that is large enough to allow maximum airflow, but small enough to maintain a strong vacuum signal in the primary venturi(s), which in turn determines how much fuel is required to achieve the proper air/fuel mixture.
In theory, if the bore and venturi are too large, the signal will be weak at low engine speeds. As such, fuel will not be pulled from the carburetor's discharge ports accurately and the air/fuel mixture will be lean. The opposite of this effect is when the carburetor's bore and venturi are too small for the engine's airflow demands. While throttle response will be outstanding, the engine's maximum power potential will be diminished.
The ideal carburetor will move the maximum amount of airflow through the carburetor and intake manifold, while maintaining the strongest possible signal. This was very evident when we spent a day at Pony Carbs, testing various carbs on a small six (see the tech article on our dyno results).
It is important to use a CFM calculator to select the proper size carburetor for your CFM requirements. However, the calculated results are just that, calculated. Once you have done the calculations, consider the following "Rules of Thumb" before you make your final decision.
Rule of Thumb |
Bigger Carb |
Smaller Carb |
Results in More Horsepower |
Results in More Torque |
Results in a Higher RPM Range |
Results in a Lower RPM Range |
Prefers Higher Compression Ratios |
OK with Lower Compression Ratios |
Best with Higher Rear Gear Ratios |
Best with Lower Rear Gear Ratios |
Prefers More Cam Duration |
Good with Lower Cam Durations |
Better with Manual Transmissions |
Better with Automatic Transmissions |
Better with High Stall Converter |
Better with Low Stall Converter |
Needs More Mechanical Adv. |
Needs Less Mechanical Adv. |
Sizing the Carb Based on Usage.
For street motors and/or city driving, it's better to start with a smaller carb, which provides maximum torque, throttle response, and fuel economy. If you do a lot of highway driving you may want to go with a carburetor that's a little bit bigger. A slightly larger carb will sacrifice some low-end torque, throttle response, and/or fuel economy, but it will give you more top-end horse power for passing and cruising. If you do a combination of highway and city, it's better to size the carb on the smaller side, rather than larger, especially when fuel economy is a primary concern.
Next lets talk about drag racing, where low-end torque, throttle response, and/or fuel economy are not a concern. In this situation a larger carb is required to achieve maximum horse power at wide open throttle. However... while bigger is better, you still don't want to oversize the carb. This is where dyno testing comes in handy, or for those on a tight budget, numerous test-n-tune passes. It also helps to have a several carbs on hand.
Finally we have the mild performance motors, or those used for Street/Strip applications. These motors usually require a carb sized somewhere in-between Street and Strip. Basically, you simply need to decide what size carb best suits your own particular needs. You may even decide to run two carbs. Maybe you'll run a 32/36 Weber during the week, driving to and from work, as this will give you the best economy and overall driveability. Then swap to a 38/38 Weber on Friday night, so your ready for that long weekend cruise with your local Mustang or Falcon club. Or maybe you'll swap to a Holley 500 in preparation for a weekend of drag racing. In any case, remember it's always better to go smaller when selecting a carb for street use.
VE or Volumetric Efficiency
Volumetric Efficiency must also be figured in to your CFM calculations. A stock small log head with a 1-7/16 carb bore (commonly referred to as a 1.5" bore) will normally see about 65% efficiency do to the restrictive nature of the log intake. The later large log heads will do slightly better at 75%, and fully ported may reach as high as 85%. An aluminum head should get around 90%, while a fully ported version can reach 100%. Turbo charging the log heads, large or small, will net huge improvements in the efficiency, as the short comings of the asthmatic log manifold are greatly diminished. In such cases the VE may reach upwards of 120% efficiency, depending on the amount of boost.
In the chart below, we have done the CFM and VE calculations for a daily driver or weekend cruiser. If you're building a race motor, increase the size by 50-100 CFM, as the motor will require more airflow when operating in the higher RPM ranges. It's easy to see how the CFM requirements change, based on the various modifications.
Block |
Cylinder Head |
Modifications |
200ci |
250ci |
Stock Motor |
Early Small Log |
Stock valves |
200-210 |
255-265 |
Mild Build |
Early Small Log |
Large valves |
240-250 |
300-310 |
Performance |
Early Small Log |
Port & Polish |
275-300 |
325-335 |
Stock Motor |
Late Large Log |
Stock valves |
220-245 |
295-320 |
Mild Build |
Late Large Log |
Large valves |
255-280 |
325-350 |
Performance |
Late Large Log |
Port & Polish |
295-320 |
375-400 |
Stock Motor |
Converted Log |
Stock valves |
235-260 |
295-320 |
Mild Build |
Converted Log |
Large valves |
275-300 |
345-380 |
Performance |
Converted Log |
Port & Polish |
315-340 |
395-420 |
Stock Motor |
OZ-250-2V |
Stock valves |
250-275 |
315-340 |
Mild Build |
OZ-250-2V |
Large valves |
290-315 |
365-390 |
Performance |
OZ-250-2V |
Port & Polish |
335-360 |
420-445 |
Stock Motor |
Aluminum |
Stock valves |
285-310 |
355-380 |
Mild Build |
Aluminum |
Large valves |
330-355 |
410-435 |
Performance |
Aluminum |
Port & Polish |
375-400 |
475-500 |
Stock build: 5500 rpm - Mild build: 6000 rpm - Performance: 6500 rpm |
Once you've determined your CFM requirements, the next step is to select a carburetor. The biggest decision is whether to use a one barrel (1V) or upgrade to a two barrel (2V). With all the different carburetors that are available, this may be very confusing, but its really pretty simple and straight forward.
The other thing you need to think about when doing a carb swap, is the ignition system. If you're replacing the stock Autolite 1100-1V carb, you'll need to swap out the distributor as well. The early (63-67) 1100's came with a "Spark Control Valve" and were designed to work hand in hand with the stock "Load-O-Matic" distributor. Even if you have a Petronics Ignition system, which eliminates the points, you still haven't resolved the problem. And while the later (68-69) 1100's carbs eliminated the "Spark Control Valve", you'll still want to ditch the stock distributor in favor of a Duraspark or DUI.
Simply put, the early distributors were a piece of junk. Do yourself a HUGE favor and get rid of the stock distributor. It will be the best money you've ever spent, guaranteed. I have a lot of customers call in asking how to resolve their carb issues, and the first thing I tell them is to replace the stock distributor. Nine times out of ten, a good ignition system will resolve their carb issues, or should I say, what they assumed were carb issues. If your going to replace the carb, why not start with the ignition system first, since it has to be replaced anyway. You may be surprised.
CAUTION: For more information, please read our tech article on the Load-O-Matic distributor and how it works hand in hand with the Autolite 1100-1V carb. Before you swap carburetors, it is essential to understand the differences between the various distributors and how these differences relate to selecting the right carburetor. |
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Autolite 1100
carb with a "Spark Control Valve" (circled) |
First, lets go over your carb choices for a one barrel. In the early years Ford used Holley-1904-1908-1909 carburetors from '60-63, and the more common Autolite 1100 from '63-69. All of these carbs had 1-7/16 inch carb bores. The Autolite 1100's were offered on the 170 and 200ci, with three venturi sizes (1.00/1.10/1.20). Mustangs normally had the 1.10 or 1.20 depending on the model year, configuration, and engine size. In '69 most sixes got the larger Carter YF carbs, which were first use in California to lower emissions on the '67-'68 model years. However, some models came with the Autolite 1101. Ford switch to the more common Carter RBS for the '70-'73 models, which came on all 250ci engines. The 1101, YF, and RBS carburetors were larger, with 1-11/16 inch carb bores.
The Autolite 1100's are fine for stock applications, but they obviously come up short in the performance arena.
Many inline enthusiast prefer upgrading the early log heads and smaller Autolite or Holley carburetors to a late model cylinder head with the larger Carter-YF and RBS carbs. While this increases the engines power output, most of the additional power is the direct result of the of the late model large log cylinder head, with it's larger valves and increased manifold volume, rather than the carburetor itself. However the larger carburetor, which increases CFM, certainly doesn't hurt.
While Autolite carbs are commonly considered to be the best carbs ever built, the Autolite 1100's were designed and manufactured before Annular Fuel Discharge technology was developed. As such the Autolite 1100's don't measure up or perform nearly as well as their bigger brothers (2100/4100 series carbs), which incorporate annular discharge boosters.
The early Autolite 1100's (63-67) also used a Spark Control Valve (SCV), which was designed to work hand in hand with the Load-O-Matic (LOM) distributor. However, the later 1100's (68-69) were designed without a Spark Control Valve. Please read our tech article on the Load-O-Matic distributors for more information on this subject, as it's important to know how they operate, especially if you are planning a carb swap.
Another option for using one barrel carbs, is to install triple one barrels. This is done by installing a custom manifold produced by Offenhauser, which bolts to the top of the existing log manifold. To maintain low end performance, the setup utilizes progressive linkage. As such, the engine runs on the center carb most of the time, and only kicks in the outer two carbs when they are needed. Triple one barrels are also hard to beat if your looking for some great eye candy to spruce up your engine bay, however they do come at a price. Triple carbs are difficult to tune, and to keep tuned, so they require regular maintenance. Another drawback is that the cylinder head has to be machined to accept the new manifold, and the linkage needs to be modified accordingly. Finally, by the time you purchase the manifold, linkage, carbs, air cleaners, and hardware, this upgrade can get a little on the pricey side.
For more detailed information see 1V Carburetors, which covers the various 1V carbs that were used on the Ford small six.
One of the most popular modifications for increasing horse power and performance, is to install a two barrel carburetor on the existing log manifold. This can be accomplished with a 2-1 adaptor, or by machining and modifying the log manifold, which is commonly called a "2V Conversion". Each method has advantages and disadvantages, so you'll need to know the differences to make the best decision.
The most common mistake when installing a two barrel carburetor, is installing a carb which is simply too large for the application. The engine might actually make less power, and may stumble and fall flat on its face when you push the peddle to the medal. Most DIY, backyard mechanics simply ignore CFM calculations and install the biggest two barrel carb they can get their hands on, thinking they are going to haul ass once it's installed. They couldn't be more wrong, and they are most certainly going to be disappointed with the results.
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CARB CHOICE
In general, if you want a little more performance, but still want to maintain throttle response and mileage, a smaller carb will work better. On the other hand, if your not overly concerned about mileage and/or driveability, and you want maximum top-end performance, a larger 2V carb may be a better choice.
Holley and Autolite carbs can be installed on stock or fairly mild performance motors using a 2-1 adaptor, however they may not be the best choice. While you might get a little more top end power, you can almost certainly expect to see hesitations and flat spots under hard acceleration, at lower rpm's, and off idle. They certainly won't be an out of the box installation, which means you'll need to re-jet the carb to get it to a point where it is satisfactory, if this is even possible. In fact, some suppliers won't even sell you a two barrel carb if they know it's going on a stock log style cylinder head via an adaptor. In most cases, Holley and Autolite carbs should only be used on large log cylinder heads, and preferably on a head that has had some work done to increase airflow, such as larger valves, porting, or a 2V Conversion. A performance cam and headers are also recommended, as well as milling the cylinder head (reducing the size of the combustion chamber) to increase the compression ratio.
A far better choice for stock or mild performance motors would be the progressive 32/36 Weber DGV, or the Holley/Weber 5200, which is a Weber carb manufactured by Holley. The progressive Weber is a two barrel carb, but it differs from Autolite's and Holley carbs, in that the secondary throttle plate doesn't open until the carb is at 2/3 throttle. The advantage of this is simple. As a progressive carburetor, it operates as a one barrel carb most of the time, with the secondary only opening when its needed, under hard acceleration and/or wide open throttle. This reduces the likely hood of hesitations and/or flat spots under normal operation, and it greatly improves throttle response and fuel mileage. Yet the added airflow of the secondary venturi increases acceleration, passing power, and overall top-end horsepower. If you want to maintain throttle response and fuel economy, while adding a little more top-end horsepower, the progressive Weber's are an excellent choice for stock or mild performance 170/200ci motors with a stock small log cylinder head.
If you insist on installing a synchronous carb (both throttle plates open at the same time) via an adaptor, on a stock or a fairly mild performance motor, you'll be better off using one of the smaller Autolite carbs or the Weber 38/38 DGS. You can also use a Holley 350cfm, but only when the carb has been properly tuned and adjusted, which includes the use of a custom metering block, which we'll cover in a separate tech article (coming soon).
The reason we like Autolite carbs, is because they are available in several different sizes, making them much easier to size to your motors specific CFM requirements. The Autolite 2 barrel (2V) carbs also incorporate Annular Fuel Discharge, which helps to diminish the effects of over-sizing the carb. In other words, while you may still have hesitation and flat spots under acceleration, they may not be quite as noticeable. In most cases, the 1.01 (240cfm) or 1.02 (245cfm) carbs work best. On the other hand, if you have a large log head which has been reworked and converted to a two barrel carb, what we call a 2V Conversion, the larger Autolite's and/or a Holley carb may work nicely, providing they are properly tuned.
It should be noted that there are kits are available to add annular discharge to Holley carbs, however they may diminish the CFM ratings slightly, as the annular boosters are larger in diameter and take up more space inside the venturi, thereby reducing airflow.
REMEMBER: The idea is to choose a carburetor that is large enough to allow maximum airflow, but small enough to maintain a high-speed airflow signal through the venturi(s). Use a CFM Calculator, then select an appropriately sized carburetor. In general, smaller carb for driveability and mileage, larger carb for top-end performance. It's that easy..... |
Holley 2V
Holley offers two sizes, 350cfm and 500cfm, which are available with manual, electric, or hot-air chokes. Both carbs are synchronous, which means both barrels open at the same time. Unfortunately this also means they are more prone to hesitation and flat spots under sudden acceleration, especially if your using a 2-1 adaptor. Therefore in most cases, the smaller the carb the better. However if your motor has a performance rebuild and/or a modified cylinder head (2V conversion), the likely-hood is greatly reduced or eliminated all together. It all depends on the CFM requirements of your specific motor. Normally the 350 has better throttle response and low end torque, with less top end power. The 500 offers more top end power, but it sacrifices lower end power, throttle response, and mileage, and there is a greater chance for hesitation and/or flat spots.
For more information on Holley carbs, please see our tech article (coming soon).
Autolite 2V
Autolite carbs, also synchronous, are available in seven different sizes, making them much easier to size to your motors CFM requirements. Ranging from 240cfm to 424cfm, they are available with manual, electric, or automatic hot-air chokes. Not only can you can select a smaller carb, which is better suited to your CFM requirements, they also incorporate a feature called Annular Fuel Discharge, which greatly reduces the likely-hood of hesitation and flat spots under acceleration. For stock or mild performance applications, we usually recommend the 1.01 (240cfm) or 1.02 (245cfm). For performance motors we recommend one of the larger Autolite's, a Holley, or the 38/38 Weber, depending on the situation, and the CFM requirements of your specific engine build.
For more information on Annular Fuel Discharge, please see our tech article on Autolite Carburetors. It should be noted that kits are available to add annular fuel discharge to Holley carbs, however the larger annular boosters slightly diminish the CFM ratings.
Autolite 1V Carbs |
Autolite 2V Carbs |
Size |
CFM |
Size |
CFM |
Size |
CFM |
1.00 |
120 |
.098 |
190 |
1.14 |
300 |
1.10 |
150 |
1.01 |
240 |
1.21 |
351 |
1.20 |
185 |
1.02 |
245 |
1.23 |
356 |
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1.08 |
287 |
1.33 |
424 |
Weber 2V - 32/36 DGV or Holley-Weber 5200
Weber offers several carbs, in various styles (side-drafts, downdrafts, etc) and sizes, with manual, electric, or hot water chokes. The most commonly used carb on a stock or mild performance engine is the Weber 32/36 DGV, which is a progressive down-draft carburetor. As a progressive carburetor, it operates as a one barrel most of the time, using the smaller primary venturi during light acceleration and cruise. The larger secondary venturi only opens when it's needed, at 2/3 throttle, under hard acceleration and/or wide open throttle. This vastly improves throttle response and mileage, and it greatly reduces the likely-hood of hesitation and flat spots during acceleration.
Weber 2V - 38/38 DGS
If your not overly concerned about mileage and driveability, the synchronous 38/38 Weber is a great way to increase performance. The advantage Weber carbs have over other carburetors, is that they are infinitely tunable. In the hands of a qualified tuner the Weber carb can be tuned to out perform any other two barrel carb, when it is sized correctly for the application. The only drawback, is that it takes a qualified tuner to get them running at peak performance. Hence the reason so many backyard mechanics prefer the Autolite and Holley carbs.
In the coming months (as time permits) we will be adding several tech articles on the Weber carbs, simply because very little information is available on the internet.
Classic Inlines stocks 32/36 and 38/38 Weber carbs, as well as carb adaptors, linkage kits, fuel regulators, and air cleaners. For more information on Weber Carbs, click here.
CFM RATINGS
One final point to consider is how 1V and 2V carbs are rated, as compared to how 4V carbs are rated. All one and two barrel carbs are rated at .3 inches of pressure drop through the carb, while all four barrel carbs are rated at .15 inches of pressure drop, which is more accurate. For example; a Holley 500-2V carb flows 380cfm when it's rated like a 4V carb. As such a 480-4V actually flows considerably better than a 500-2V (380cfm), even though the Holley 500 appears to be the larger carb.
NOTE: For more information on sizing your carburetor properly, please see our tech article on Calculating CFM.
INSTALLATION
The most common method for installing a two barrel carb is accomplished using a 2-1 adaptor. The adaptor merely changes the bolt pattern and bore size of a one barrel manifold so it accepts a two barrel carb. They are several different adaptors available, some work with Autolite and Holley carbs, others with Weber carbs. Carb orientation also varies depending on the design of the adaptor, however most adaptors install the carb with the throttle plates parallel with the crankshaft. Bottom line, make sure you purchase the right adaptor for your application. Classic Inlines now offers billet adaptors for most applications. If we don't have what you need, let us know and we'll see what we can do.
Note: Classic Inlines also offers phenolic spacers, or insulators, which provide a thermal barrier to prevent heat soak (transfer of heat to the carb). This is a common problem with our sixes, with the carb sitting directly over the exhaust manifold or header, as heat transfers upward to the intake manifold and carburetor, resulting in vapor locks and/or diminished performance.
The other option for installing a two barrel carb, is using a special conversion plate or adaptor, which allows you to hog out the intake making it a true two barrel opening. This method, called a 2V Conversion, requires machining the log intake. As such, the cylinder head must be removed for the modification, then reinstalled when the modification is completed. However this isn't all bad, as its a great time to install larger valves, new valve guides, hardened seats, and if your budget permits, a little port work . It's also a good time to CC the chambers and increase the compression ratio, which is accomplished by milling the head (reducing the size of the combustion chambers) and/or installing a thinner head gasket. You can also install deck the block and/or install flat top pistons to increase the compression ratio, however this requires pulling the motor and disassembling the short block. In most cases we recommend using dished pistons and zero decking the block on 200ci engines, as this improves the quench. However zero decking isn't possible on 250ci engines, as zero decking would result in compression ratios that are way to high. As such, we normally recommend flat top pistons for the 250ci, then decking the block and/or milling the head accordingly, to archive the desired compression ratio.
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The 2V Conversion method is by far the best way to install a 2V carb on a log intake manifold. Regardless of which carb you select, the power gains are substantially increased when the log intake is opened up to accommodate a two barrel carb. It also increases low end torque, due to the increase in air velocity at lower rpm's. Classic Inlines did a lot of dyno testing last summer and the results verified our suspicions. Adding a 2V carb via a 2-1 adaptor generally netted 4-5HP, while a converted head bumped the power by 20-25HP, or more, depending on how the motor is built (cam, headers, etc). That's a huge difference considering we used the same carburetors. The only difference was the method used to install the carbs. For more information, see our tech articles on 2V Conversions and Dyno Testing.
In the near future Classic Inlines plans to offer modified large log cylinder heads, which will be rebuilt and converted to use a two barrel carb. We may even offer one that's set up for twin two barrel carbs. You can save a core charge by sending us your cylinder head, or you can purchase a core from us, if we have one in stock. Remember, we only modify large log heads. We do not modify small log heads, since it's a waste of money (a stock large log head outflows a small log head, regardless of how much work is done to the small log head). Classic Inlines also offers a wide range of services, including new or oversized valves, unleaded valve seats, valve guides, valve springs, retainers, viton seals, and freeze plugs. We also do multi-angle valve jobs and back cutting, CCing and reshaping the combustion chambers, 2V Conversions, porting and polishing, flow testing, and any other machine work required. We also offer furnace brazing, aluminum and cast iron welding, and we can repair most cracked or damaged cylinder heads. All cylinder heads are cleaned, hot tanked, and magna-fluxed before we start work, and pressure tested when the work is completed.
Autolite 1V |
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Advantages |
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Allows use of original distributor (with SCV), or an aftermarket distributor. |
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Allows the use of existing carb linkage and air cleaner. No modifications required. |
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Out of the box install, making it the easiest carb swap. Built for your application. |
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Does not create hood clearance issues, like some carb swaps might. |
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Keeps the engine bay stock, which is required for a contours restoration. |
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Disadvantages |
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Autolite 1V carbs are notorious for hesitation and flat spots, and hard starting when hot. However, these problems are usually eliminated when you buy a rebuilt carb from Classic Inlines. |
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Limited power potential, due to the smaller size of a 1V carburetor. |
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Requires frequent maintenance (rebuilding) to maintain peak engine performance. |
Offy 3-1V |
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Advantages |
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Center carb functions as primary, and outer carbs as progressive secondaries. |
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Maintains fuel economy, yet provides additional power when needed. |
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Offers old school Hot Rod appearance, which is a show stopper. Great eye candy. |
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Vacuum secondaries eliminate the likely-hood of hesitations and/or flat spots. |
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May cause hood clearance issues, depending on adaptor and air cleaner height. |
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Disadvantages |
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Requires the removal and reinstallation of the cylinder head. |
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Requires machine work and modification to the log intake. |
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Requires modification to the throttle linkage. |
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Requires continued maintenance to keep carbs in tune. |
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Increased return spring pressure may cause leg and foot fatigue on long drives. |
32/36 Weber 2V |
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Advantages |
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Operates on primary 80-90% of the time, secondary only opens when needed . |
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Maintains throttle response & fuel economy, yet provides added power when needed. |
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Allows two barrel carb swap on an otherwise stock motor, without over carbing. |
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Vacuum secondary eliminates the likely-hood of hesitations and/or flat spots. |
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Disadvantages |
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Requires modification to the throttle linkage. |
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May cause hood clearance issues, depending on adaptor and air cleaner height. |
38/38 Weber 2V |
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Advantages |
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Increased horse power for performance street motors. |
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Maintains throttle response & fuel economy when properly tuned. |
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Excellent carb for highway use, providing more passing and cruise power. |
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Disadvantages |
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Requires modification to the throttle linkage. |
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May cause hood clearance issues, depending on adaptor and air cleaner height. |
Autolite 2V |
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Advantages |
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Carbs are available in eight different sizes to meet your specific CFM requirements. |
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Incorporates Annular Fuel Discharge, which in itself has numerous advantages. |
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Annular discharge reduces hesitation and flat spots, when compared to a Holley 2V. |
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Disadvantages |
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Requires modification to the throttle linkage. |
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While hesitation and flat spots are reduced, they may still occur under acceleration. |
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May cause hood clearance issues, depending on adaptor and air cleaner height. |
Holley 2V |
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Advantages |
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Both sizes are readily available, as are parts for tuning and maintenance. |
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Resulted in the highest HP gains, using a 2-1 adaptor, during our dyno testing. |
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Cost may be lower due to availability. Easy to find at swap meets, new or used. |
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Can be modified to accept Annular Fuel Discharge boosters. |
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Disadvantages |
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Only available in 350 and 500 CFM models, which may result in over carbing. |
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Hesitation and flat spots are likely under hard or sudden acceleration. |
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Requires modification to the throttle linkage. |
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May cause hood clearance issues, depending on adaptor and air cleaner height. |
2V Conversion |
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Advantages |
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Yields the highest power gains possible from a 2V carb. |
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Allows the use of any 2V carb, without adaptors. |
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Ability to use any aftermarket air cleaner. |
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No hood clearance issues. |
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Cleanest looking installation. |
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Disadvantages |
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Requires the removal and reinstallation of the cylinder head. |
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Requires machine work and modification to the log intake. |
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Requires modification to the throttle linkage. |
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Of all the 2V upgrades, this is the most difficult and costly. However, that being said, it also offers the greatest gains. Like the old saying says, "You get what you pay for".
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If your building a stock or mild performance motor, and you want to maintain the stock appearance, the Vaporizer can't be beat.
This is especially true if your building a concurs restoration, where you need to keep the motor stock, or when you don't want to modify (temporary or permanent) the existing carb linkage or a numbers matching cylinder head.
If your building a stock or mild performance motor, and you want the added punch of a two barrel carb, there are a couple ways you can go. The Progressive Weber is a good way to go when you want to maintain mileage and throttle response. The only modification required to complete the install, is to modify the existing carb linkage, however that's usually pretty simple. A lot of guys just switch over to a throttle cable. The only problem is that no one makes a kit, yet. If you leaning more towards performance, rather than mileage and/or driveability, then a 38/38 Weber, a smaller Autolite, or a Holley carb, work great.
If your building a performance motor, and you can't afford the OZ head or our aluminum head, a late model, large log cylinder head with a 2V conversion is the only way to go. The best way to do this, is to purchase a second cylinder head, and work on it as time and money permits. This way you won't be rush and wind up taking short cuts, and you can work on it when your pocket book allows, rather than trying to do it all at once.
If you already have a carb sitting on the shelf, grab a 2-1 adaptor and install the 2V carb on your existing log head, while your working on the conversion head. The experience you'll gain tuning the carb will be invaluable when you go to install the converted head. And if you get frustrated tuning the 2V carb, or run out of time, you can simply remove the 2V carb and adaptor, reinstall the one barrel, and go back to it when you have more time and patience. For carb selection, a larger Autolite, a Holley 500, or the 38/38 Weber, are recommended. Another option is to go with multiple carbs. Maybe triple one barrels, or twin Weber's?
Finally, if your building a performance motor with an OZ-250-2V head or Classic Inlines aluminum head, you have several options. You can use a large two barrel carb, a four barrel carb, twin two barrels, triple two barrels, triple one barrels, a throttle body, or multiple throttle bodies. The sky's the limit, providing you have a large pocket book.
If you really want to add some punch to your small six, add a turbo or super charger. Of course that's a whole new subject, which requires a tech article all in it self.
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