How To Choose a Carbureted Intake Manifold
Let’s face it there’s a ton of aftermarket intakes out there from mild to wild, but how do you know which one is right one for your engine? Choosing the correct Intake manifold can pay huge dividends with increased power and additional torque for your engine. But only if you make an educated decision.
Let’s take a quick look at a stock intake manifold. The plenum in a stock manifold is typically on the smaller side, this helps keep the air velocity high. Likewise, the cross-section of the runners is also fairly small, this keeps the air moving at maximum speed and the fuel atomized going into the cylinders. These small runners provide good idle quality and crisp throttle response, but the small size also limits the amount of air the manifold can flow at higher rpms. Eventually the engines going to reach a point where it’s trying to pull more air in, than the stock intake can actually flow. This is the point at which a stock intake manifold needs to be upgraded to a performance manifold with a larger plenum and larger runners.
As with most situations when building an engine, the intake manifold should be matched to your intended purpose for the engine. Be sure to consider the engine combination that you are building or already have. Will your project be a daily driver or is it going to be a weekend warrior for the strip or track? These are some important questions to ask yourself, so be realistic with your answers. Throwing a bunch of mismatched parts at your engine, more than likely isn’t going to give you the performance your looking for.
Everyone likes a big tunnel ram with dual quads sticking through the hood, but it’s probably not the most practical set-up for your weekend cruiser. Intake manufactures advertise RPM ranges identifiying where their intakes are the most efficient. For example, an intake manufacturer may advertise a range of "1,500-6,500 RPMs". Taking into consideration this advertised rpm range, is one of the easiest guides to use when choosing the right intake for your engine.
Most street cars work best with a dual plane intake, and most advertise an rpm range of "idle to 6,000 RPM" or "1500-6500 RPM" because that is the rpm that they be running at most of the time. Race cars typically produce their power more in the upper RPM ranges and will require a single plane intake with a 2,500-8,000 rpm range". You also need to consider the physical fitment, be sure to select the appropriate part number for your engine and cylinder head design. And look for any specific features you may need, like engine vacuum ports, water coolant ports, carburetor flange fitment, and don’t forget to check for proper hood clearance, before you close the hood!!
Let’s take a look at a dual plane intake. They’re named for the split plenum opening just below where the carburetor sits and each side of the opening feeds 4 of the cylinders on a V8. Dual plane intakes are popular on performance street and some mild racing applications since they generally build power across a wider rpm range starting at idle to 1,500 RPM, depending on the manifold. Every intake has its own performance characteristics, so It's best to know how you plan to use your vehicle and select an intake from there. Our Weiand Street and Speed Warrior dual plane intake manifolds are an excellent choice for performance in this rpm range. Holley and Weiand carry a variety of dual plane intakes in several configurations including 2x4 and 3x2 set-ups. They are an excellent choice for a performance intake in this rpm range.
In a Single plane intake all the cylinders share the same intake plenum. Fuel and air from the carburetor enters the intake through this one opening without any separation unlike the dual plane. This single hole feeds all 8 cylinders on a V8. Single plane intakes are typically less restrictive and work best for building power between 3,000 and 8,000 RPM's. Because of the higher RPM range, a single plane intake manifold is best suited for racing applications and not so much for you daily driver. Holley Strip Dominator and Weiand’s Track Warrior and Team G intakes are excellent intakes, designed to perform in this power band range.
If you’re looking for something outside the box, Check out Weiands line of Hi-ram intakes. They’re nostalgic looking single plane intakes that you can run a single or dual 4bbl set-up with. And a more modern look can be had with one of our Sniper sheet-metal fabricated intakes they too are available in single and dual 4 bbl configurations.
You’ll also hear the term low rise and high rise manifold. Both these terms refer to the overall height of the intake manifold but can also help to identify the rpm range that they work best in. There is no standard or set height where low rise intakes end, and high rise intakes begin. But low rise manifolds are usually similar in height to stock intake dimensions. They offer good hood clearance and most applications allow you to build your combination without having to cut a hole in your hood or adding a hood scoop. Low rise can also identify the runner length and rpm range as well. The shorter, closer to stock length runners will perform closer to the factory rpm range, and offer great throttle response right off of idle and throughout the rpm range.
High rise intakes on the other hand are better at building horsepower in the upper RPM range and typically have larger and longer intake runners. The power band of a high rise usually starts around 2700 to 3000 rpms and they can be capable of making power all the way through 7000 to even 8000 rpms.
The last bit of info that you’ll need to consider when selecting an intake manifold depends directly on which carburetor or throttle body you plan to use. For street use you’ll likely find 2 choices of mounting flanges. First is the 4150 or commonly referred to as the square bore style. This design uses 4 holes of equal size or it may one large square hole or even 2 elongated holes for the intake opening. They’re designed to work with a wide variety of Holley, Quick-fuel, Brawler and Demon carbs with the 4150 flange.
The second design is called the spread-bore, it can also have 4 holes or you may find spread-bore manifolds with a large single hole or even 2 elongated holes. But if you look closer you’ll see that the opening is larger towards the rear portion. If we take a look at this Holley spread-bore carburetor you’ll notice that the front holes or primary venturis are smaller in diameter compared to the rear or secondary holes. The odd shape of these intakes allows clearance for the larger secondary venturis found on spread-bore carburetors. If you happen to find a manifold you like but it’s not available for your particular carburetor, there are plenty adapters available to mount a square bore carb to a spread-bore intake and vise versa.
The 3rd choice you’ll run into is the 4500 Dominator style intake. These are typically single plane intakes designed for racing or high horsepower applications. They have a much larger mounting flange which allows you to mount one of our Dominator carburetors to them.
So now that we have covered the basics, you can see just how important intake manifold selection is. Remember to match the rpm range of the manifold with rpm range of your other engine components. And you’ll will be happier in the long run and so will your engine!
To see our full line intake manifolds and intake accessories, visit our website at Holley.com
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