The Stromberg 97 might not be the most commonly used carburetor on today's hot rods, but when it comes to plain old popularity, it's still at the top of the list. Nothing looks cooler on top of a traditionally dressed Flathead or small-block (or Nailhead or Y-block or Hemi or ...) than two or three or six of these time-honored two-barrels. We can't explain exactly what makes something cool, but these carbs qualify, which is why hot rodders coast to coast are scouring swap meets, boneyards, classifieds, and eBay for these holy grails of hot rodding.
It's far too common, however, to find out too late that the batch of what you thought were 97s were in reality either Holley 94s or Stromberg 48s or 81s, or were in such horrible shape that no amount of cleaning and rebuilding could resurrect even a single carburetor.
In the next few pages we're going to give you some tips on taking the trouble out of finding and fixing old 97s. We'll also take a look at those long awaited, brand-new 97s coming out of England.
The BeginningIn 1908, the Chicago Police Department bought its first motor vehicle, the Cubs won their last World Series, and in a one-room shop near the waterfront, a Swedish immigrant named Alfred Stromberg and five business partners incorporated the Stromberg Motor Devices Company.
Stromberg was manufacturing brass carburetors with glass fuel chambers at the rate of one per week, but production grew as demand rapidly increased. The company provided carbs for cars, tractors, and World War I aircraft. By 1929, when Bendix Aviation acquired the company and moved it to South Bend, Indiana, Stromberg employees were producing 4,000 carburetors a day.
Early in the '34 production year, Ford decided to replace Detroit Lubricator carburetors on their V-8 engines with Stromberg 40s. The similar 48 model replaced the 40 as the standard carb in late 1934. The 97 appeared on the '36 models and continued through early 1938 on the 221-cid flatheads. The smaller 81 carb was used in 1937 and part of 1938 on the 136-cid V8-60 engine. In the middle of 1938, Ford switched from Strombergs to Holley 94 carburetors.
The 97s continued to be manufactured as aftermarket replacements for later carburetors and gained a lot of aftermarket support. When Vic Edelbrock started manufacturing aftermarket speed equipment in the early '40s, his first product was the 180-degree "Slingshot" manifold, built for dual 97s.
Today, almost 70 years after Ford quit running Stromberg 97s, hot rodders all over the world continue to buy and rebuild these old carbs.
97s, 48s, And 81s How Are They Different?In the simplest terms, the three most prevalent Stromberg carburetors vary in size from the 48 (largest) to the 81 (smallest).
To the uneducated eye, it's hard to tell the difference between the various models of Strombergs, which can be frustrating at the swap meet or boneyard. Frequently the sellers don't even know what they have and unintentionally mislabel the carburetors they're selling.
We asked Sperry Hutchinson at Rodworks and Chad Blundell at Blundell Speed & Machine for tips on telling them apart. Despite internal differences, the 48 and 97 top air horns will fit each other's bodies, which makes things more confusing if they've been mixed and matched. The 48 and 97 bases are interchangeable and may both be marked EE-1. The 81 base can be spotted by its smaller size and may be marked EE-7/8.
Many 97s are easily identified by the raised circular casting on the outside of the bowl that may or may not be marked with a large raised number 97. Unfortunately, this is not true in every case. Sometimes the number 97 may be small, or the circular casting may be blank. A 48 can frequently be identified by a tiny number 48 cast into the same location. The 81 body is visibly smaller inside than the other two models. The side of the bowl will frequently (but not always) be marked with the numeral 81.
A more dependable method for telling these two apart is to look on the opposite side of the outside of the bowl where lettering has been cast. The 97 should be marked with a 31/32 symbol. The 48 will be similarly marked with a 1 1/32 symbol. The 81 will be marked with 13/16.
An easy way to check if the carb is a 97 is to check the inside of the air horn. A 97 has a choke linkage ball detent that holds the choke open. The 48 doesn't have that, so the inside casting is smooth.
Why Are 97s The Favorite?All the old Strombergs are in high demand, as are Holleys, but 97s are definitely the favorite among rodders. Ed Wimble, who just started manufacturing brand-new Stromberg 97s, thinks that part of the reason 97s are everybody's favorite is nostalgia. The 97s were the carbs more frequently used for multiple carb setups on hot rods in the early days. The fact that they continued in production and had a lot of aftermarket support also helped maintain their popularity. The 97s gained a reputation in racing, and their 155-cfm rating was better suited to the Flathead engines of the era. Double or triple 48s, which flow approximately 170 cfm each, can be too rich of a setup for a typical street Flathead. We'll talk about determining the right carburetion for your engine in a few minutes.
Treasure Or Trash?Once you're confident that you can identify your swap meet treasure, you still have a lot of scrutinizing to do. Sperry, Chad, Ken Isidor from Ken's Carburetors, and other rebuilders we spoke to all expressed frustration in how many old 97s are too far gone for a rebuild, but provided these tips:
1. Check the air horn, main body, and base for pitting, especially along the mounting surfaces. Make sure that all flanges are flat. Sperry brings a piece of glass to lay against the flanges, then holds the part up to the light to spot potential leaks. Minor problems can be resolved with a surface block and emery cloth, but removing too much material can interfere with the accelerator pump ratio and other elements. The cover of the fuel bowl that is attached to the air horn is a rectangular shape fastened with a triangular screw pattern. Years of over-tightening can cause the outer corners to warp, which may be unsalvageable.
2. Pay attention to how the throttle plates fit in the base. Reject any that are severely pitted or corroded, or that aren't flat. When you hold them up to the light, there should be a thin ring of light all the way around each plate. Not enough light could mean stuck plates. Too much light could mean flooding the engine.
3. Look for stripped threads. Chad recommends bringing along a fuel inlet jet for checking the threads in the inlet fitting.
4. Inspect the float pin. If the brass pin has been cranked in too tight, it can start to leak.
5. Look for bowls that are porous or caked with residue. The residue can be cleaned out, but it may be hiding pinholes in the bowl.
6. Be sure the idle adjustment screw ports in the base haven't been filled in by a previous owner, who might have used the carburetor in a multi-carb application.
7. Make sure the emulsion tubes haven't been damaged by over-tightened jets, which restricts the air supply.
8. Look for sloppy up and down throttle shaft movement, a sign of worn bushings.
9. Check for discarded choke blades.
10. Make sure the extended throttle shaft goes all the way through the base. This allows you to run your throttle linkage on either the passenger side as it was from the factory, or on the driver side, which is how many aftermarket throttle linkages are hooked up.
Gathering up half a dozen salvage yard carbs is no guarantee that you'll have enough decent parts to put together one that is functional, but knowing what to look for can save time, money, and aggravation. And take it for granted that you will treat any pre-owned carburetor to a cleaning and rebuild before running it.
Counting CarbsHow many 97s should you run on your engine? Are dual 97s enough? Is three too many. Six looks cool, but does it make sense?
There are plenty of hot rodders out there who answer those questions based on how many carburetors they can afford, how many they already own, what looks good, or what kind of intake manifold they've got hanging on the wall. To be fair, many of the cars running radical Stromberg combinations are either show cars or "shock rods," neither of which are built for maximum performance. Tuning these simple carbs to meet the performance standards of those cars is not difficult.
On the other hand, three 48s flow 45 cfm more than three 97s. That much extra air could cause a flat spot when you get on the throttle. As Chad Blundell put it, "the more you know, the more rubber you can burn!"
Determining the optimal carb combo involves figuring out your engine's airflow capacity, which is measured in cfm (cubic feet per minute). The formula to determine airflow is rpm multiplied by displacement divided by 2 (because the engine displaces half its overall capacity each intake stroke). The resulting number is then converted from cubic inches into cubic feet by dividing by 1,728 (cubic inches per cubic foot).
It looks a lot simpler on paper:(rpm x displacement) / (2 x 1,728) = cfm or more simply(rpm x displacement) / 3,456 = cfm
Let's say your 239 flathead displaces 275 ci. At 4,500 rpm the arithmetic would be: (4,500 x 275) / 3,456 = 358.07. Your engine's theoretical maximum airflow capacity at 4,500 rpm is 358 cfm.
Unfortunately, theoretical airflow is not actual airflow. Street engines operate below maximum capacity. The ratio of how much air your engine can pump to how much it does pump is called volumetric efficiency (VE). As a general estimate, VE hovers around 75 percent (0.75) for stock engines, 85 percent (0.85) for modified street engines, and 90 percent (0.90) or above for race engines.
To find the actual airflow for that modified street Flathead, multiply the theoretical airflow by the VE estimate of 85 percent (358 x 0.85 = 304). That Flathead is flowing approximately 304 cfm, so a pair of 155-cfm Stromberg 97s is just what it needs. Which might be the long way of saying that the manifold hanging on the wall may have been the right choice after all.
The New 97sThe ultimate solution to the problem of finding, identifying, and repairing Stromberg 97s comes in an orange, black, and white box. Ed Wimble and Clive Prew from Suffolk, England, were surprised to discover that, despite the popularity of these carburetors, the patents had expired, and nobody owned the Stromberg Carburetor name. They knew they had to do what old Alfred did almost 100 years earlier-answer an increasing demand for Stromberg carburetors by putting them back into production.
Before actually reproducing the carbs, Stromberg Carburetor Ltd., began manufacturing individual components. The company Web site offers a long list of 97 carburetor components; not only expected items such as jets, gaskets, and rebuild kits, but virtually every single component, except the castings.
Eventually Ed and Clive obtained copies of the original drawings, which allowed them to begin reproducing complete Model 97 carbs to the original dimensions, specifications, and casting details from the 1930s. The inlet needles and seats sizes are precise, and the venturis have a true 31/32-inch diameter.
In the process of duplicating a 70-year-old product, the new company chose to take advantage of modern materials and manufacturing processes. Parts that had been made from zinc- or cadmium-plated steel are now stainless. The zinc air horns and bodies and cast-iron bases are pressure die-cast in new dies, and CNC-machined as opposed to the old gravity casting process. Gaskets are a high-tech, reinforced cellulose/nitrile material.
The most valuable piece in the box might be the instruction literature. When's the last time you got a manual with a swap meet Stromberg?
Some of our tightfisted hot rodder friends have sniffed at the price tag for the new 97s (in the neighborhood of $400), but when you add up the time and money you've spent searching for old 97s and various mystery variations, cleaning and repairing them (or paying somebody to do it), and discarding unusable carbs, the price of a correct, complete, perfect condition, fresh-out-of-the-box 97 starts to sound a lot more attractive.
Stromberg has been building up a network of dealers in the United States. The current list can be found on their Web site. Stromberg is currently working on building a 200-cfm version of the 97 in addition to a reproduction 81.
Rod & Custom will be covering the installation of a pair of these repro 97s in the near future, so stay tuned for the full story on bolting them up, along with some seat-of-the-pants driving impressions of these new and improved Strombergs.
Main jet Venturi Air flow* Power valve 97 0.045” 31/32 (0.97)” 155-cfm 65 (0.0350” diam metering hole) 48 0.048” 1 1/32 (1.03)” 170-cfm 63 (0.0370” diam metering hole) 81 0.035” 13/16 (0.81)” 125-cfm 71 (0.0260” diam metering hole)
*Air flow is approximate on old Strombergs due to inconsistencies in the castings
