Carb Signal
"Engine displacement, camshaft duration, intake manifold design, and torque-converter stall speed each play a factor in determining the amount of signal a carb will have. The signal is the pressure difference between the atmosphere above the carburetor and the internals of the intake below the carburetor, which draws the air/fuel mixture through it. Venturi size and style (straight-leg, down-leg, annular) are used to determine the most suitable carburetor for a given application. Frequently, a manifold designed with overly large ports and plenum will suffer from a low signal condition at the boost venturi. Transmission types and stall speeds also affect whether a mechanical or a vacuum secondary carburetor is needed. On a vehicle with a manual transmission or a converter with a stall speed of 3,000 rpm and above, we recommend a carburetor with mechanically operated secondary throttle plates. With lower stall speeds, we recommend vacuum-operated secondaries."
Carb Sizing
Big carbs look hot, and some magazines are guilty of plopping on carbs that are too big for sheer intimidation factor. Our advice is not to be like them, since a carburetor that is correctly matched to an engine combination will give both optimum performance and drivability. "The most common error in carburetor selection is choosing one that is too big," says BG. "Big carburetors make headlines in magazine stories, but usually don't provide the best drivability. A carburetor that is too big may idle poorly, hesitate at part-throttle, and become lean at wide-open throttle. It's best to ask the carburetor manufacturer or a competent engine builder for their recommendation in order to avoid costly mistakes."
Carb Spacers
Similar to changing jets, carb spacers can be used as an effective tuning device. Since a motor reacts differently to varying heights and configurations of spacers, trial and error is often the best method of selecting the proper spacer. While the effect of a carb spacer is barely noticeable on some engines, others will show significant gains or losses. "Generally, an open spacer will increase top-end performance, whereas a four-hole spacer improves low-end torque," BG explains. "An open spacer has the effect of increasing plenum volume, while the four-hole spacer gives the effect of a longer runner."
Alcohol
With an air/fuel ratio of about 6.0:1, methanol carburetors consume almost twice the fuel of their gasoline counterparts. To accommodate their greater fuel flow requirements, the needle-and-seat assemblies of a methanol carburetor are much larger, measuring 0.150 inch compared with 0.110 to 0.130 inch in a gasoline carb. "The power valves in a methanol carburetor are designed for higher flow, and the jets, air bleeds, squirters, and passage sizes are changed to suit the needs of the methanol carburetor," BG explains. "Furthermore, methanol absorbs moisture from the atmosphere, which is detrimental to cylinder walls, combustion chambers, valvetrain, and oil. Consequently, oil changes and engine rebuilds must be conducted at shorter intervals. However, methanol engines regularly produce more torque than gasoline engines, and run cooler and more consistently."
New Products
Maintaining market presence requires continually updating your product line, and Barry Grant has several exciting products that will soon be available to the public. "We are concentrating on getting our new BadMan inline four-barrel carburetor to market," says BG. "We're currently producing our initial production batch of carburetors in-house from billet aluminum, in the hope that they'll be available by September. Also, with the recent surge of interest in hot rods with Stromberg 97 carburetors, we've finalized new carburetor designs to enter that market called the Demon 98!" CHP