Four Barrel Inline Carb - Meet The Bad Man

Barry Grant's new inline four-barrel carb is likely the most innovative induction system since the advent of electronic fuel injection.

By Steve Dulcich

Photography by Johnny Hunkins

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 Roots
It 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 Better
While 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 Details
While 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.