Stromberg 97 and the Holley 94 - 97 Nuances

When Ford was getting ready to release the new 24-stud Flathead he contracted with the Chandler-Groves Company to develop an entirely new, more efficient carburetor and produce them for the 1938 production run. In exchange for that agreement, Ford was granted the patent on the new design and when the year was up he went looking for a better price on carburetors. Holley was able to cut the price by less than 10 cents a piece and became the sole supplier of 94s until production came to a halt in 1957.

Now that new versions of both carburetors are available, the debate over which is better could go on indefinitely. The Holley 94 has two 15/16-inch venturi while those of the Stromberg 97 measure 31/32 inch. It would seem obvious that the slightly larger 97 should flow more, however their numbers are almost identical. Although Stromberg 97s and Holley 94s share the same three-bolt mounting pattern, there are a number of significant differences between the two. The fuel inlet is in the float bowl top of the 94s, rather than the side of the bowl as on the 97s. The 94s use a center-hung float as opposed to the side-hung design of the 97s. Finally, the 94s used spray bars for discharging fuel in the main system, while the 97s used emulsion tubes. All that being said, dyno testing has revealed that there is no significant difference between the two designs. The Stromberg is slightly better at producing horsepower in relation to the fuel consumed at low speeds (below 2,500 rpm) and the Holley is better above that range-but the difference is roughly 1 hp. So, why were 97s more popular than 94s on hot rods? One advantage of the 97 is that when multiple carburetors are used the main jets can often be changed without removing the carburetor from the manifold, not possible with 94s. Of course in a race environment that was important, on a street engine not so much. The other issue with 94s was the enrichment system.

Strombergs used a mechanically operated power valve that is only activated when the throttle was wide open and the engine can use the extra fuel. Holley's enrichment system used a vacuum-operated power valve that opened to supply extra fuel to the engine when the vacuum dropped to a certain point, usually 7-1/2 inches Hg or less. The problem is that when two or more carburetors are used, the vacuum signal drops earlier and more aggressively than with a single carburetor. As a result, when using multiple carburetors the power valves may open prematurely, making the mixture much richer than necessary. This is easily cured by selecting a power valve that opens at a lower value. Another issue with using multiple 94s is their size. Slightly larger front-to-back than a 97, fitting three 94s on some manifolds can be a problem (a situation some responded to by grinding down the front screw boss on the float bowl).

New Old Carburetors Stromberg Carburetor
Not long after Stromberg Carburetor of England was formed and began producing new 97s and parts there were some conflicts within the management that interrupted manufacturing. The rumor mill was quick to provide all sorts of false information, however we're happy to report that the issues have been resolved and the company is in the capable hands of Clive Prew.