Vic Edelbrock’s 1938 purchase of a 1932 Ford Roadster marked a turning point in his small company’s history. By designing and manufacturing the first Edelbrock intake manifold, Vic Sr. started the hotrod era. Edelbrock Sr. knew that a strong top-end design might liberate horsepower. He designed the first 180-degree dual-plane performance intake for Flathead V8s. Choosing the correct intake manifold for your build is more than just finding the biggest one. For best results, experts recommend matching the head and intake to the rpm range.
If you only compete on the drag strip every now and then, you may want an intake that is good for both the street and the strip. Engine manufacturers must be able to interpret performance components that blur the distinctions between street and race. It should have a smooth shape and moderate segment transitions. The intake manifold’s design and direction affect an engine’s efficiency. Major contour changes can reduce air entering the combustion chamber.
What are the Best Intake Manifolds
While there are many styles to pick from, each design has certain compromises. Consider the dual-plane manifold. Its performance from idle to 5,500-6,000 rpm has been appreciated. OEMs utilize this manifold because it is easy to drive. The cylinder runners are split by 180 degrees of crank rotation. A V8 engine has two distinct independent plenums, each feeding four opposed cylinders. Remember that air velocity impacts throttle response and low-end torque when choosing an intake. That’s why oversized port runner volume cylinder heads may not function as well as stock. Turbulence improves airflow into the cylinder and improves the air-fuel mixture for better combustion. Wet flow testing can help determine what is causing the fuel to separate from the air in the combustion chamber.
Carbureted intake manifolds include dual-plane, single-plane, airgap, and tunnel ram. Matching the intake style to the vehicle and anticipated rpm range is key.
Air and fuel mingle in the plenum as it passes through the runners into the combustion chamber, giving these intakes their “wet flow” nickname. Contours or induction pulses allow fuel droplets to separate and fall out of the suspended air/fuel combination in wet flow designs. These engines use a “dry flow” manifold. The dry flow manifold is more sensitive to heat, which is why racers place ice on their plenum between rounds.
For carbureted applications, most intakes are either dual-plane or single-plane, and both have advantages. Dual-plane intake manifolds have two independent plenums that accept air fuel from the carburetor. Each plenum feeds four of the eight cylinders. The split design lets each bank of four cylinders observe every other firing pulse, reducing induction pulse overlap. Better induction pulse at low rpm. They have longer intake runners, making them suited for low and middle power.
The open plenum architecture of single-plane intake manifolds feeds all eight cylinders of a V8 engine. The dual-plane clean induction pulse is not provided at low rpm, but the flow distribution between cylinders is improved. For a higher air volume, single-plane intakes use shorter, straight runners. For high-rpm power up to 8,000 rpm, these intakes are employed mostly in racing.
Once you’ve decided on an intake manifold style (and rpm range), you need to find one that matches your engine. Consider hood clearance, which may dictate whether you can run a hi-rise or lo-rise intake, cylinder head port form, oval, square, or other? Then there’s the carburetor’s mounting position and size. In street applications, hood clearance is critical. If you wish to keep the standard hood without a hood scoop or low-profile air cleaner, you’ll need to measure the stock manifold’s height and choose a performance intake that matches it.
Choosing the correct manifold that fits the induction pulses to the intake valve generates a supercharging effect, pushing a bit more air/fuel into the cylinder. “How this works is your intake air will come in, pass through the throttle body, and then start traveling down the intake runner on the intake stroke for the cylinder,” he adds. Your valve closes just before the air enters. As a result, the air still possesses velocity. It forms a pressure wave that pushes back up to the plenum and then starts to come back down after bouncing off the plenum.
After bouncing back and forth for a bit, the pulses start to diminish, and the effect goes away. When the intake valve is open, this pressure wave will return to normal. “You may add more air to the cylinder and produce more power. This effect is only helpful for a very narrow rpm range because if the timing is off, the effect is lost. One reason to employ a variable intake manifold to generate another range.”
When choosing a manifold, consider the cylinder head port style. There are other port types, including rectangular, oval, and peanut-style, so make sure the intake ports match the cylinder heads. Consider your carburetor’s mounting pad arrangement. Four-barrel carbs exist in three styles: square bore, spread bore, and Dominator. Assemble the intake to the mounting pad. Use the same throttle body inlet size for a fuel-injected manifold.
Last but not least, consider plenum design. An Australian performance engine components maker says plenum capacity and geometry affect intake manifold performance. There are various theories underpinning plenum volume and form design, but the foundations are the same. A tiny plenum dome on an intake manifold might produce poor low-end performance. You’ll be choking the engine since it’s out of air. A high plenum capacity can cause poor air-fuel distribution to all cylinders and sluggish engine response. Today, a performance intake plenum dome requires a lot of care.
A well-designed manifold that is well matched to the engine’s needs will provide more torque and horsepower. An intake manifold connects the carburetor or throttle body to the cylinder head ports. It is part of the induction system that must fit the cylinder head and camshaft airflow characteristics to the engine displacement and rpm range.