Manifold Essentials

Flip through the pages of a current issue of the most popular automotive enthusiast magazines and your eyes will likely distort from the flash and pop of the technical wonders on display. Computer generated images dazzle the senses, horsepower promises reach unheard of pinnacles. But wait, what about the fundamentals of engine basics? Reality, it seems, is obscured by a composite of delusory photos and bikini clad young ladies.

This is not to suggest that technology, offering electronic innovations, or the use of computers and on-line information sites is a bad thing; that is what progressive thinking is all about. The automotive performance industry has always been nurtured by evolution and we applaud every new discovery.However, not every street rod owner is an advocate of technical wizardry for their own personal use. To the contrary, in many cases the street rod owner loves the idea of today's high technology, but in reality, simply wants a smooth running, dependable machine that can be driven on rod runs, on picnic outings, to and from shows, all without worry about a malfunction requiring a white coat garbed technician to unravel. In many ways today's street rod owner is a retro-personality.

Place simple function in the same column with do-it-yourself and you get a clear description of most street rod owners. Half the fun of owning a hot rod is hanging out in your garage, bench racing with friends and doing projects offering personal gratification. As part of this process, the installation of aftermarket parts and pieces plays a significant role as a popular activity. Taking things one step further, we unveil the purpose of this story. Under the category of aftermarket parts installation of a replacement manifold seems to rank high on everyone's to-do list. The reasons vary from improving the capabilities of an original engine to building a brand new high-performance engine. Whatever the case, installation of a manifold is easily within the reach of any street rod owner willing to spend the time. There are only two impediments that come to mind once a manifold project is decided on as a project; how to do the job correctly and choosing the right manifold for the application. The impetus of this story is to meet these primary objectives without hassle and with professional results.

Our first objective would be establishing key points to be aware of when investigating the basic fundamentals in choosing a manifold for a street-driven application. Nothing fancy, or complicated in the choice; good performance and reliability the only prerequisites.

Next, we wanted to clarify the best methods for installation easily performed by the enthusiast. The search for answers did not take long. What better place to garner the information we required than from a icon in the performance industry, a company in the business of designing and manufacturing manifolds for over 60 years, the Edelbrock Corporation. As has been the tradition since 1948, the door to the dyno-room was thrown open for a magazine writer to spend time gathering information for readers. The idea was to talk to the crew, get the straight story on picking the right manifold and how to do the job of installation correctly. It is not rocket science, we were told, just a matter of common sense, basic knowledge, a few tools and considerable patience. Curt Hooker, engine builder, racer, long-time employee and keeper of the dyno-room's secrets offered to answer our questions. First on our list of inquiries, what is the purpose of a manifold and what type is best suited for the average street rod application?

In its simplest terms, a manifold is a device that is made up of a defined series of passageways, which distribute a fuel and air mixture from outside to inside the cylinders. And, without getting into exotic and/or custom designs, there are two basic styles of manifold design addressed to the street rod enthusiast. The two types are a single-plain and a dual-plain design. Without calling on a complicated engineering hyperbole, a homespun explanation of a single-plain manifold is that of a giant room (the plenum chamber) with eight doors (the valves). This common area (room) is filled with fuel and air, when a valve or door to the cylinder opens, the air and fuel mixture rushes in through a runner. In a dual-plain manifold the (plenum) or room is divided into two chambers located at different elevations or plains. There are many advantages to a dual-plain style manifold, including the fact that the air/fuel charge can alternate between the two chambers throughout the firing order.

This design is referred to as a 180-degree manifold; with four cylinders firing from one chamber and four from another. Edelbrock has taken the dual-plain design one step further with its all new Air-Gap system. This system features an open air space that separates the runners from the hot engine oil in the valley portion of the block resulting in a cooler, denser charge. The Air-Gap manifold design is available for small-block Chevy, big-block Chevy, Chrysler 340/360 and 5.2L and 5.9L Magnum engines, and Ford small- and big-block models.Now, back to the question at hand, what manifold is best for the street rod driver? Again, the underlying component is vehicle use. The average street rod owner uses their vehicle for weekend outings, rod runs, driving to and from various shows, some long distance trips and a mix of highway and city traffic situations. The key ingredients needed to meet these aforementioned demands would be reliability, simple operation and total driveability. The overwhelming choice suggested by the crew in the Edelbrock dyno-room was a dual-plain designed manifold because of its inherent characteristics of excellent throttle response, adequate torque, good low- to mid-range power and, when using a single four-barrel carburetor, reliable. At this point in the story we need to jump back to the beginning and remind the reader, that when you initially begin planning the engine to be used in a street rod, set realistic goals, choose a manifold and fuel system combination that will make driving easy, fun and low maintenance while providing good performance and dependability. There is a plethora of choices to be made if you decide on using a dual-plain style manifold, and to illustrate the point, we used the Edelbrock product line as examples.

Beginning at the bottom of the horsepower food chain, there is the Performer series of Edelbrock manifolds, featuring a dual-plain, low-rise design. The Performer series is street legal in 50 states. The Performer offers its best power range from idle to 5,500 rpm.

One step up would be the Performer RPM, with a high-rise design and providing its best power from 1,500 to 6,500 rpm. And, as mentioned, the newest design, available in both the Performer and Performer RPM series, is the Air-Gap manifold. It should also be mentioned that Edelbrock has just introduced a pair of Performer RPM manifolds for the LS-1 engine, 1998 and later, that comes in the Camaro and Firebird and the 1998 and later LM series (4.8L, 5.3L and 6.0L) found in the GM pickup truck series. These engines are popular engine swaps for street rod applications. One very distinct advantage of this new manifold is the fact that it comes as an assembly including a MSD timing control box, so all of the OEM sensors can be attached. And, by using the MSD box, the factory control box can be set aside making this a very easy swap. In simple terms, the manifold includes a kit converting an EFI engine to a carburetor engine replacing the factory map sensor with the MSD unit.

During our conversation on simple manifold combinations, the question of EFI could not be discounted. Edelbrock does offer a line of Performer fuel-injection manifolds to replace stock units and it offers a compete EFI system for the Performer and Performer RPM manifold called the Pro-Flo Multi-Point EFI system. The only comment on using EFI for a street rod application is cost. The more involved the system, the more money is needed for the project.

As long as we are on the subject of cost, the question arises, what if you just are not satisfied with a simple, low-profile manifold/carburetor combination? Of course, at any rod run, or roadster show, there are always a few exotic engine setups getting a large share of comments like, "Oh man, look at that!" from passing spectators. It is only fair that we consider this approach to street rod performance. According to the guys at Edelbrock, they offer what the catalog calls their Dual Quad, a manifold designed to offer maximum performance between 3,500 and 7,500 rpm. It should be noted that although the Dual Quad, with two, four-barrel carburetors, offers the monster motor image, it is difficult to tune, and lacks smooth performance on the street at low rpm. Many street rod owners, who choose the monster look, offset the problems by using a progressive linkage setup allowing the engine to cruise at low speed using only the rear carburetor and engaging the front unit only with full throttle position. With this method, you can have the look without some of the negatives. Edelbrock also offers a retro-look setup using three, two-barrel carburetors on its "three deuce" manifold designed for '55-86, 262-400 cubic-inch engines.

This particular manifold carries a history back to 1955 when the first version was introduced by Vic Edelbrock Sr., beginning the small-block Chevy revolution. Today, as in the past, the carburetors are activated with progressive linkage, allowing low-speed performance using only the center carburetor. (Note: the three-deuce manifold does not come with carburetors as part of the package.)

So far, we have spent a lot of effort on the small-block version of street rod performance, so what about the big-block? The same answers can be related to most big-block applications, the Performer, Performer RPM and Air-Gap manifolds are available in most of the popular big-block configurations, and will fill the same order of performance perimeters found in the small-block versions.Before continuing, there are several precautions and noteworthy bits of information regarding choosing a manifold and relating that choice to a total concept.

It should be noted that the Chevrolet small-block has two very distinct types of manifold design. The early models feature a six-bolt per side manifold and the Vortec version, 1996 and later, feature a four-bolt per side design. The number of bolts used to secure the manifold is not the only difference. The early model six-bolt per side manifolds have the bolts entering on an angle and on the Vortec version the bolts enter straight down in a clamping effect. The two styles have different torque readings for the bolt tightening sequence. Care should be exercised when installing the manifold bolts to avoid damage. Under the heading of interesting bits of information, we discovered that the Edelbrock Thunder Series carburetors, especially the 650-cfm version (in manual or electric choke), were labeled the best choice for the basic street rod engine up to 400 hp when used in combination with a Performer manifold. It was concluded, by a unanimous vote, that the average street rod owner, wanting nothing more than to be able to drive to and from events, go cruising without worry and in general use their hot rod for fun should consider the following formula: An engine with a power curve from idle to 5,500 rpm, the use of a dual-plain manifold to obtain good torque characteristics, throttle response and mid-range power coupled with a four-barrel carburetor that is easy to tune and offers reliable performance. Not everyone will agree, but it is a good starting point.

On the list of precautions, comes one echoed by Edelbrock engineers as well as the crew in the dyno-room. Before choosing a manifold fuel system combination, take time to consider the total picture. The total engine package should be explored before any final decisions are made. It is very important that the internal parts of your engine are matched in their function with the external parts. Example: an engine with stock factory camshaft, pistons and rods inside, equipped with a supercharger, two four-barrel carburetors, a nitrous system on the outside may not perform up to expectations. This is one reason why Edelbrock has taken the time and testing research to create the total power package concept. With this idea, the camshaft and related parts are matched to the manifold and carburetor combination to provide the best possible performance with the least amount of hassle. If a customer chooses not to use the Edelbrock camshaft package, they can contact the technical department at the Edelbrock headquarters in Torrance, California, and the crew will consider the customer's camshaft, depending on lift and duration, and suggest the manifold and carburetor combination best suited for the job.

In fact, the consensus of opinion offered by the Edelbrock staff was to do your homework before buying. Don't just walk into a local speed shop or national chain auto parts store and have the counter salesperson chose a manifold for your needs. They just may sell you what they have the most of instead of what you need. Do your own research, talk to other enthusiasts, to engine builders, or someone with a lot of experience. You can call or e-mail the Edelbrock technical hot line. You can go on-line. What ever method you chose, get advice before buying.

INSTALLATION
The installation of a replacement manifold is not an unachievable task, but it does require the proper tools, common sense, a little patience and careful procedures. To get some first-hand tips on the correct methods we spoke with Curt Hooker, of the Edelbrock engine building department, who installs the company's products on a daily basis.

If the manifold is a replacement for a factory unit or a installation on a newly built engine the steps to a successful conclusion are basically the same.Clean the gasket surfaces on the heads, getting rid of any signs of old gasket material or other corrosion. Check the manifold mating surfaces to be sure they are clean and free of imperfections. Just because a manifold is fresh out of the box does not mean it can't have a miss placed part hung up in one of the runners. Curt recommends a coating of Edelbrock Gasgacinch sealing material on the head surface and the backside of the gasket. Let the bond dry slightly then place the gasket in its proper location. Curt then suggests a tiny bead of silicone on the front side of the gasket to aid in sealing. It should be noted that many of the new style gaskets have a thin silicone seal built into the gasket material on the manifold mating side. You can now apply the end seals and sealant around the water inlet. Next, carefully place the manifold straight down onto the engine block head surfaces, making sure you do not disturb the gasket position.

With the manifold in position, the fastening bolts are next. Here, the plot thickens slightly. The recommended method for installing and tightening the bolts to their correct torque readings is to work from the center out. Using a torque wrench is necessary to achieve the proper specifications. Curt suggests that you tighten the bolts in two stages; a lower torque reading for the first applications, then a final tightening to recommended specifications. All Edelbrock manifolds come with instructions and torque specifications. However, a note should be made regarding the Chevrolet small-block, as there are two very distinct types of manifold design with different torque specifications. The early model manifolds have a six-bolt per side pattern that has the bolts entering the engine on an angle. The late-model Vortec block has a four-bolt per side design with the bolts entering straight down. Also, the newest gaskets for the Vortec engine are self sealing, some having a rubber O-ring built in for a better seal. The Vortec and the early models have very different torque readings, and you must follow proper procedures to avoid damage to the manifold. It seems to be a unanimous feeling that the late-model, Vortec-style manifold with its straight in bolt design offers excellent clamping pressure and a better seal.

A question asked by many do-it-yourself enthusiasts is should manifold bolts be installed wet or dry? Curt Hooker suggests that a small amount of lubrication on manifold bolt threads will prevent galling. Actually, there is little danger of thread stretching on manifold bolts, as could be the case with head bolts, because torque readings are not high enough to cause a problem. One suggestion worth noting, however, is to place a small amount of silicone on the bottom thread area on bolts protruding into the block valley to prevent oil from working up into the outer surface of the manifold bolt recess area. As for manifolds bolts, it was recommended that aftermarket hardware replace stock factory bolts. Aftermarket bolts, like those manufactured by companies like ARP or Edelbrock, are of a higher quality and in some cases, factory bolts with large heads could interfere with manifold designs. Also, using manifold bolt washers to evenly distribute torque and to prevent galling is a useful suggestion.

In conclusion, the selection and installation of an aftermarket performance manifold on your street rod is a matter of taking some time to research your needs, chose a quality product, keep everything simple, and use common sense in determining a street friendly combination. Also, rely on a manufacturer for advice and service. With all of the instant methods of communications (e-mail, Fax, on-line web pages and the old fashion telephone) a street rod enthusiast should be able to count on a manufacturer to offer support and guidance when choosing a manifold.