Take your pick. Whether you choose to let nature fill your engine's cylinders with 14.7 psi of absolute pressure or you cram a bit more in the hole with a blower, Weiand has you covered. For about as long as our hobby has existed, the company has been providing top-notch intake manifolds and superchargers to the salivating masses.
In the decades since their inception, aftermarket intakes and blowers have made tremendous progress thanks to a wave of technological innovations and cutting-edge CNC advancements. To learn more about the modern state of induction, we got together with Jay McFarland and Jim Dralle of Weiand. A multitude of factors determine which induction combination is best for a given application, so it seems rather wacky to skim aimlessly through a parts catalog and hope for the best. In addition to helping you maximize the potential of your top end, the boys at Weiand shared some fascinating info on what goes into designing high-performance intake manifolds and blowers.
Forced induction motors necessitate lowering the static compression ratio, and traditionally the tradeoff is a loss of low-rpm torque before the motor makes usable boost. However, since roots-style blowers offer such immediate off-idle torque, this is less of an issue than with other forms of forced induction. "When building a new engine specifically for use with a roots-style blower, we recommend a maximum static compression ratio [CR] of 7.5- to 8.0:1," says McFarland. "If you already have an engine you are retrofitting, you can use the formula below to determine your effective compression ratio [ECR]. If it is above 10.5- to 11.0:1, you should go with race fuel."
ECR= (Boost PSI/14.7+1)x CR
Considering all the different cylinder heads on the market, selecting the right intake manifold for your engine combination can be daunting. "With both cylinder heads and intake manifolds, the cross-sectional area of the ports or intake runners controls the velocity of the incoming charge, which is what most strongly affects cylinder filling at a given engine speed," says Dralle. "It's important to understand the engine speed where peak torque should occur and how broad the power curve should be for your application. Dual-plane designs typically provide a broader power curve, especially between 2,500 and 6,500 rpm, whereas single-plane designs should only be used where a narrower powerband is acceptable at engine speeds above 6,500 rpm. Furthermore, customers should feel free to use the information given by reputable manufacturers and also use their tech lines."
Selecting the right blower requires determining how large a blower your application requires, and the first step in doing so is making sense of the different nomenclature. Weiand offers many series of blowers such as 142, 144, 174, 177, 250, and 256. On Weiand's smaller blowers, the number represents the volume of air in cubic inches that the blowers move per revolution. For example, the144 series blower produces 144 ci of air per revolution. On the company's larger 6-71 and 8-71 blowers, the number refers to the original GMC labeling scheme. "GMC designed the 6-71 blower for a six-cylinder motor displacing 71 ci per cylinder, hence the name," McFarland explains. "An 8-71 was designed to feed an eight-cylinder motor displacing 71 ci per cylinder. That said, a 6-71 blower moves 411 ci of air per revolution, and an 8-71 moves 436 ci per revolution."
Manifold Design Parameters
"Despite their simple outward appearance, countless factors such as runner volume, runner cross-section, and plenum volume must be considered when designing an intake manifold. Runner volume is a function of the charge-air passage length and cross-sectional area. The passage length determines the engine speed at which the pressure waves within the inlet passage best promote cylinder filling. Cross-sectional area is always a balance between providing velocity to aid inertial filling at the end of induction cycle before the intake valve closes, reducing flow restriction during the pumping portion of the induction cycle and providing a good pressure-wave signal to the passage inlet. Plenum size affects how the pressure waves generated by engine operation will aid cylinder filling, while plenum geometry contributes greatly to cylinder-to-cylinder air and fuel distribution. Unfortunately, the least interesting but most important factor in designing intake manifolds for the performance aftermarket is optimizing design within the packaging constraints given by vehicle applications. Other important factors are casting design, casting tooling, manufacturing techniques, and new raw materials that are now available." -Jim Dralle
"Even if you've gone through the effort of porting your heads, it doesn't necessarily make sense to port the intake manifold. A wise porter once explained that it's not the material that's removed that's important, but the material that isn't removed. Unless proper development and validation testing is performed, most intake manifolds are best left unported. Good port matching usually won't do any harm and will typically provide a 5-10hp gain. This is especially true when the flange exit size has a smaller cross-sectional area than the upstream charge-air passage, which is sometimes the case since a single manifold design must often fit several different cylinder head designs. Usually, enlarging the flange opening area larger than the upstream charge-air passage cross-sectional area will not yield any power gains." -Jim Dralle
Choosing the right carburetor is critical when installing a blower. Under boost, an engine needs 40-50 percent more air and fuel, so picking the correct carb is the key to being able to make full boost. "Generally, it's safer to have a carb that's a bit on the large side rather than the small side in order to prevent a precarious lean condition," McFarland advises. "Additionally, two smaller carbs often promote more even fuel distribution compared to having a single large carb in the center of the motor. Holley offers supercharger-specific carburetors that feature a boost-referenced power valve to prevent a lean condition and that are calibrated for use with a roots-style supercharger." A simple formula to determine the proper CFM requirements of a carb is:
CFM = Engine CID x Max RPM/3456 x (Max Boost PSI/14.7 + 1)
Powerboat blowers are different animals from automotive blowers, so there are a few things to keep in mind if you score a sweet deal on a boat blower at the swap meet or are thinking about putting an automotive blower in your boat. "Blowers that utilize a toothed belt incorporate a pop-off valve to relieve pressure in the advent of a backfire, which prevents stripping off all of the teeth from the belt," McFarland explains. "However, pop-off valves can't be used in marine applications due to their enclosed engine compartments and the risk of explosion they present. Consequently, Weiand's smaller marine blowers do not have a pop-off valve, instead relying on a serpentine drive pulley that will allow the belt to slip in a backfire situation. We do offer 6-71 and 8-71 kits for higher-horsepower applications, but they're for open-air engine compartments only."
Airflow is power. Getting exhaust out of your motor is just as important as getting air into it. Since blowers increase the exhaust gases produced compared to a naturally aspirated motor, using a free-flowing exhaust system and larger primary tube headers is very important. "As a rule of thumb, if you are producing 6-10 pounds of boost, the bare minimum for small-blocks is 15/8- to 13/4-inch headers, 3-inch collectors, and dual 21/2-inch mufflers," says McFarland. "For big-blocks running the same amount of boost, shoot for 17/8- to 2-inch headers, 31/2-inch collectors, and dual 3-inch mufflers. For small-blocks running over 10 pounds of boost, use a minimum of 17/8- to 2-inch headers, 31/2-inch collectors, and dual 3-inch mufflers. Big-blocks running more than 10 psi will require 21/8- to 21/4-inch headers, 4-inch collectors, and dual 31/2-inch mufflers."
Big or Small?
"Since each motor is different, it's hard to generalize how much power a blower will add, but here are some basic points of reference. Our smaller blowers on a stock small-block Chevy running 6-7 pounds of boost will result in an increase of approximately 100-120 hp. Add a mild blower cam and a larger carb, and you can expect a typical small-block to produce anywhere from 360 to 400 hp. With a good set of heads, you can reach 440-470 hp. Upgrading to a larger blower such as a 6-71 could push the output to well over 500 hp. It's important to understand that an engine does not know what size supercharger is bolted to it. The boost produced by the blower is a bigger factor than the actual size of the blower. So the estimates above are somewhat typical of any Weiand blower. An important characteristic worth noting is that at low rpm, smaller blowers typically produce more torque than bigger blowers. Conversely, at high rpm, larger blowers produce substantially more power than smaller blowers." -Jay McFarland
If not for the fact that most people expect intake manifolds to fit under the hood, then all motors would have tunnel-rams. Dralle says that the best inlet duct for a given engine will have uniform charge-air passages with the correct length and cross-sectional area and a passage inlet geometry that is straight with minimal wetted surface area. "Due to the packaging considerations for most passenger cars and race cars, dual- and single-plane carbureted intake manifolds are designed to perform best within the compromises created by packaging constraints," Dralle explains. "A tunnel-ram style intake manifold can be more closely designed to the optimum inlet duct geometry and is often considered the ideal design for maximizing power and torque."
Although they've evolved quite a bit, roots-style blowers look very similar from the outside as they did decades ago. However, most of the significant technical innovations that have been made since then aren't noticeable to the naked eye. The product of state-of-the-art CNC machines and the manufacturing of brand new components, Weiand blowers can hold much tighter tolerances than roots blowers from the past. This allows the lobes to fit much closer to the case, which dramatically improves efficiency. "You want to ensure the parts you are using are machined to exacting tolerances," says McFarland. "If not, you will lose boost pressure. The rotor-to-rotor and rotor-to-endplate clearances are very critical, and each blower is hand-assembled with all critical clearances being checked and recorded. They are also tested in our supercharger test cell, which measures boost pressure and airflow at varying speed points up to maximum rpm."
On paper, the efficiency advantages of a centrifugal blower look good, but roots-style blowers are still extremely popular in the hot rod market. "The advantage of a roots-style blower is that it is considered a positive displacement design," McFarland opines. "This design can move a much larger volume of air at a lower rpm than a centrifugal. Roots-style superchargers produce a very flat and wide torque curve and will begin to generate power as low as 1,000 rpm. No centrifugal supercharger can produce this same kick-in-the-pants feel."
Spring-loaded belt tensioners are idiot-proof, but don't fret if you must adjust the blower drive-belt manually. "On a cold engine, grasp the belt halfway between the upper and lower pulleys on the driver side of the engine and move it in and out," McFarland explains. "When it's properly tensioned, you should be able to move the belt approximately 1 inch total, or 1/2 inch inward and 1/2 inch outward. Check the belt again once the engine is warm and it should have approximately 1/4 to 1/2 inch of play. If it is less than that, then the belt is too tight and could damage the blower or crank snout."
"People are so focused on the cfm a cylinder head flows, yet they often ignore the intake manifold. However, a cylinder head is only as good as the intake manifold it's attached to, so both are key components in an engine's overall inlet ducting. For both cylinder heads and intake manifolds, a focus on flow alone can lead to a poorly performing engine combination. Once again, having the correct charge-air velocity with the best flow coefficient, or least restrictive flow, will yield the best engine power. A poor intake manifold choice can limit the power gained by a good cylinder head, while a good intake manifold choice will maximize the performance potential of any cylinder head. The two components really work hand in hand." -Jim Dralle
Although Weiand is best known for its premium carbureted intakes and blower kits, the company is currently completing development on a new line of composite EFI intake manifolds for the LS-series engines. The new Weiand Street Warrior EFI intake was developed in conjunction with Starr Technologies of Australia to optimize the low- and mid-range power of LS1, LS2, LS3, LS6, L76, and L92 engines. "These intakes generate as much as 32 hp and 31 lb-ft over a factory LS6 intake on a mildly modified motor at 4,000 rpm," says Dralle. "They should hit the streets some time this summer."
Supercharged motors have different needs than naturally aspirated motors, so Weiand has some tips for spec'ing one out. "If you are building an engine specifically for a blower, we recommend a 7.5:1 static compression ratio, four-bolt mains, steel rods, a steel harmonic damper, and a forged crank and pistons," says McFarland. "High-flow heads will get the most out of the blower, and wider valve seat widths will help cool the valves. In addition to longer duration specs, grinding the cam on a 112- to 114-degree LSA is preferable. Lastly, a high-output ignition will ensure adequate spark to light off the denser air/fuel mixture." CHP