There is no arguing that a single four-barrel carburetor is the most prevalent induction system used in high-performance V-8 engine applications. Barry Grant's Demon line of carburetors launched headlong into the fray about a decade ago, and earned a reputation as a premier unit, taking the conventional four-barrel to a high level of refinement. Up until now, all four-barrel carbs shared the characteristic of having four venturis clustered in an essentially "square" arrangement, with the intake manifold placing the carb centrally between the cylinder head banks of the engine. This basic configuration has been in use so long, it is nearly set in stone. Thinking outside the box, the natural question is whether this common arrangement is necessarily the best. If you really think about it, the accepted configuration leaves a lot of room for improvement
There is something of an incongruity with the essential layout of eight cylinders arranged in two longitudinal banks of four cylinders, with the induction clustered from effectively a single central point. The need for a resultant central plenum, and the routing of the ports from this central local to the various intake ports of the cylinder heads, creates compromises in the intake's layout and design
In a typical single-plane application, the outer ports require longer curved manifold passages, while the inner runners are necessarily shorter, with a different radius of curvature. In a cylinder head layout with evenly spaced runners, the problem becomes even more acute, with the inner runners of the manifold becoming very short, and with almost no curvature, while the outer runners are significantly longer. Runner length is a key component in tuning the engine's torque curve, so when the lengths are all over the map, just what is the targeted tuning point? More often than not, the dictates of what can be physically fit within the manifold's space and arrangement is the intake port arrangement's final determinate, rather than any effort to tune effective runner length. Further compromises are considered in relation to the runners' junction with the plenum. Targeting the "square" plenum's corners beneath the carb is the best compromise when attempting to equitably split the plenum's contents. Again, this layout is virtually impossible to achieve in engines such as a small-block Ford, where the intake runners are not paired on the heads.
Historical RootsIt is not surprising, then, that Ford sought to find a better solution back in the "Total Performance" days of the late '60s. SCCA Trans-Am racing was in the spotlight. While multiple carbs with an appropriately designed intake manifold could reduce the manifold layout compromises, the SCCA rules presiding over the series dictated that only a single four-barrel carb could be used. Seeking to improve distribution in the induction system, Ford introduced the notorious Autolite inline four-barrel carb. The idea was to arrange all four barrels in a row, a layout that is intrinsically superior at providing mixture to all of the cylinders along the length of the engine. The original Autolite inline four-barrels were purely "race-only" carbs, and were never used on a production car. Early versions of these carbs did not even have an idle circuit. Though the basic layout proved valid then, development was short lived, since once Ford pulled out of racing in 1970, the inline carb was essentially dead.
A Good Idea Made BetterWhile the concept has been buried for over 35 years, the fundamental principle is just as logical today as it was back then. There is a purely geometric advantage to the inline layout, feeding mixture evenly along the length of the cylinder banks. What makes it even better is this inline arrangement lends itself beautifully to a plenum-ram-style intake manifold, with perfectly identical runners feeding every cylinder head port, with the runners firing in a straight line down the throat of the heads. The promise is near ideal distribution, and equal-length manifold passages that are effectively a straight extension of the cylinder head ports themselves
Leave it to Barry Grant to recognize the inline four-barrel carb's potential advantage. Always on the hunt for a definitive edge in the design of high-performance carburetors, Grant decided to pursue a logical end and explore the potential of the inline carb. Slicing sections of conventional Demon four-barrels and running the resultant pieces in the unconventional inline configuration, the potential was readily apparent. Testing was done compared to the best contemporary four-barrel manifolds, and according to Grant, the results revealed immediate and dramatic benefits. With Lambda sensors recording mixture readings in each port, the usual saw-tooth pattern of uneven air/fuel ratio delivery at idle speeds gave way to an uncanny readout of nearly perfect mixture distribution to every hole
As Barry tells it, "We thought something blew out in the mixture monitors when we saw what amounted to virtually a flat-line reading on all eight holes. Sure as can be, all of the equipment was reading on the money, we just had distribution like we'd never seen. What was even more apparent was the way the system idled remarkably smooth at low rpm, despite the fact that the engine was equipped with a stout cam. The inline setup tamed the radical cam, and gave us a fuel curve across the board we never see with a conventional four-barrel carb." Coming from a major conventional four-barrel manufacturer, we have to give Grant's word serious credibility
With the theory proven, the development team at Barry Grant went to work conjuring up a modern incarnation of the fabled inline four-barrel. What resulted from this effort will perhaps transpire to be the most significant innovation in carburetion since the introduction of the WCFB four-barrels back in the '50s. Dubbed the "Bad Man," Barry Grant's new carb is as revolutionary as it is familiar. Though the carb's layout is all-new, the tuning points, such as jets, bleeds, needle, and seat assemblies, are the same pieces used on conventional Demon carbs. In fact, a survey of the Bad Man leaves little mystery for anyone familiar with traditional carbs; the essential tuning parts and even the linkages are related to carbs we have been dealing with for decades.
Bad Man Technical DetailsWhile we have discussed the inline four-barrel configuration's potential performance benefits, actually taking the concept and physically creating such a carb involves a monumental development process. Grant's approach was to achieve the desired configuration with all-new major castings, while maintaining many of the familiar tuning components traditionally used in high-performance carburetors. The castings were designed to accommodate a wide range of bore sizes, utilizing Grant's highly regarded replaceable venturi sleeve design. The configuration allows the carb capacity to be varied over a wide range, from approximately 500 cfm to over 1,000 cfm, simply by changing the venturi sleeves. The enthusiast's real advantage is that the same carb can be calibrated in terms of airflow capacity for a broad range of engine sizes, or it can be tailored to meet the engine's needs based on rpm and power requirements. The concept is well-proven in Grant's Demon RS line of conventional four-barrels. Incorporating this system was a natural design element in creating the Bad Man
Conventional four-barrel carbs are equipped with progressive linkage arrangements, allowing the primary two barrels to open to approximately 30 percent before the secondary barrels begin to open. The reason is throttle control, since this linkage arrangement allows more precise mechanical control of throttle area at lower throttle openings. Similarly, the Bad Man is equipped with a progressive mechanical linkage, however, the arrangement opens the first and third barrels simultaneously, with the linkage picking up the second and fourth barrels further in the travel. The "secondary" barrels open at an accelerated rate so all four barrels reach wide-open throttle at the same time. The slick linkage setup essentially uses every other barrel as a primary, with the alternate barrels as the secondaries. This spreads the mixture discharge over a broader length of the intake manifold compared to any conventional four-barrel, which improves mixture distribution to all the cylinders
A notable Bad Man design element is the configuration of the major castings. Essentially, the carb comprises a main body, which incorporates integral float bowls, the venturis, and the throttle plates, with a separate air horn casting bolted on top of each primary/secondary pair. The air horn is highly contoured to direct airflow straight down the carb's barrels. Unlike conventional four-barrels with separate float bowls hung off each end, the Bad Man's integral bowl system contains all the casting's fuel, so the carb does not rely on any gaskets for sealing below the fuel level, a design that guards against fuel seepage or leaks
The upper air horn assembly contains most of the tuning parts of the carb, including the air bleeds, emulsion tubes, accelerator pump squirters, the jets, the needle and seat assemblies, floats, and the enrichment circuit. Rather than draining the fuel in a catch can, unbolting the bowls, and pulling the metering blocks, a jet change on the Bad Man is a matter of just popping the air horn lid, and swapping the conventional jets screwed inside. The fuel stays captive in the bowls, preventing much of the mess and potentially torn gaskets normally associated with a jet change. Each barrel has a pair of air bleeds, one for the main or high-speed circuit, and one for the idle circuit. Again, these are familiar parts, with the same tuning process as any other Demon four-barrel
You'll find regular needle and seat assemblies on the Bad Man's air horn, just like any other Demon carb, but this inline carb has a separate needle and seat assembly and fuel inlet for each barrel. This arrangement is capable of handling the mightiest race engine's fuel flow requirements, while providing precise fuel control suitable for a mild street driver. The floats are unique to this carb design, with paired floats swinging from a central yoke, though the adjustment procedure is the same as a regular Demon four-barrel, with Demon's excellent large sight glass giving a clear view of the bowls' fuel level
Two items that are substantially different in the Bad Man are the accelerator pump system and the enrichment (power) circuit. Rather than using a diaphragm accelerator pump as found on the Demon carbs, the Bad Man uses a piston-style pump located in the main body. Piston-style accelerator pumps are a proven design, with a long history of use in OEM carburetors. The piston-style pump is a far more suitable design for the inline carb's layout and eliminates the diaphragm pump's potential seepage below the fuel level of the bowls. With the piston pump, the amount of pump shot can be adjusted by simply changing the linkage for more or less pump stroke. With the Bad Man's rocker-style pump linkage, there seem to be endless possibilities for fine tuning the accelerator pump delivery. The shooter size controls the accelerator pump discharge rate, just like with a conventional four-barrel carb. The pump shooters on the Bad Man look similar to those used on a Demon four-barrel, however, each has a single orifice, since there is a separate squirter at each barrel instead of just one splitting fuel flow to each pair of barrels
Probably the biggest change to be found in the Bad Man's metering is the power enrichment circuit. Four-barrel Demon carbs have always used a power valve for this function, where a rubber diaphragm operates against an integral spring to open and close the enrichment circuit based on engine vacuum level. The Bad Man uses a power piston for this purpose, again a design proven in a multitude of OEM-style carbs. The power piston, like a power valve, operates against a spring, based upon the level of engine vacuum. The piston has the advantage of not being subject to rupturing or blow-out, as with a power valve, and tuning can be done by changing the spring instead of having to replace the entire assembly. The Bad Man's power piston is linked to a simple slide mechanism, which opens or closes an auxiliary fuel orifice at the main well via a Viton seal.
We took one look at the Bad Man, and immediately recognized the inline concept's value. Although the carb is radically different, on closer inspection it seemed imminently familiar. The regular tuning parts, Demon-style sight glass in the side, and even the linkage to the throttle plates, bear enough resemblance to the four-barrel carbs we are used to for us to feel right at home. One glance and you know how to adjust the idle speed, and the two idle mixture screws at the primary barrels promise easy dial-in. We can see the natural advantage to fuel distribution. According to testing at Demon, the setup accomplishes this goal so well it allows larger camshafts to operate at low engine speeds (as low as 450 rpm, according to Grant), improving vacuum and low-speed idle as well as part-throttle drivability and fuel consumption
The plenum-ram-style Aero-Ram intake is exactly the correct arrangement to make the best use of the inline carb configuration, and we suspect the straight, direct runners are nearly ideal for unrestricted airflow while taking advantage of ram-tuning effect. Grant has the small-block Chevrolet version of this induction fully worked out, while the LS1 and big-block Chevrolet versions are following close behind. We're already putting the thumbscrews on Grant's people to get one over to us for serious dyno evaluation. With the inline Demon combined with Grant's Aero-ram Triple-D intake manifold, this induction looks hot.