Today our resident Stromberg expert Steve is going to show us his step by step process on rebuilding Stromberg 97s. This step by step process can also be used with Stromberg 48 & 81s but there are some differences between the 3 models. Please comment below with any tricks that we missed!!
Tag: Stromberg 97
If you know hot rods, you know Stromberg 97, right? Whether it’s the dry lake, the drags, circle track, car show, or just a street near you, they were the go-to, go-fast carburetor for generations. And you know what? They still are, if you’re building an early style hot rod or race car. Whether you’ve got a flathead four or eight, six-pot Chevy or Lincoln V-12, or pretty much any American OHV from ’49 to ’60-something, there’s an manifold somewhere to make it move a little faster, all with the tell-tale three-bolt, two-hole Stromberg carb mounts.
So where did it all start? Strombergs have been around since the earliest of automobile days. 1909, in fact, when Alfred Stromberg and five others formed the Stromberg Motor Car Devices Company producing one brass carburetor a day. By 1928, it was 4,000 a day thanks to some 12,000 staff. And in 1929, the company was sold to Bendix Aviation, moving to join their other operations in South Bend, Indiana. Up through the 40s to the 60s you’d find a Stromberg carb on your Buick, Olds, Plymouth, Stude, even Auburn and Lincoln. But by the 70’s the writing was on the wall for carburetion. In the USA, Stromberg’s last hurrah was the ’74 GMC V-6 truck. And in Europe they stuck the name on a Zenith-designed constant vacuum carburetor, flogged to a host of popular brands including Mercedes and Lotus.
But if we’re talking hot rods, it’s all about the 97. Easy to find. Easy to tune. Good for a reported 150 cfm through 15/16-inch venturis. Original equipment on Ford V-8s for barely more than two years—1936 and ’37. Yes, as we said, the carburetor of choice for hot rodders and drag racers right up to the 1960s.
So here’s the question: Why the 97? Chandler-Groves. Ford. Holley. Carter. Rochester. They were all around at the same time. A lot of them were bigger too, which offered more bang for your buck at the time. Its replacement, the Ford/Holley ‘94’ 2-bbl was Ford’s V-8 choice for some 15 years in various guises. And there were plenty of other Strombergs to choose from too. The 1933/34 Model 40 and 48 had a bigger 1-1/32-inch venturi and a reported 175 cfm. Some Lincolns had a 1 inch 160 cfm-rated LZ version, and Ford’s thrifty little V8-60 motor came with the 81, a smaller version of the 97 with a 0.81-inch throat, making it perfect in a 2×2 for your Ford 4-banger or V8-60 powered midget.
Our hobby is full of contradictions; on one hand it’s steeped in tradition, on the other it embraces the latest technology. There are rodders, like Editor Brennan, who love the latest, high-tech components. Brennan’s gadget-oriented philosophy is “anything worth doing is worth making as complicated as possible”-if a computer, multiple sensors, and miles of wire is involved controlling any function he’s happy. Throw in a couple of blinking LEDs and he’s delirious. On the other end of the spectrum are those of us who consider simplicity the ultimate engineering accomplishment, no electronics, no wires, and the only mode is manual. Apparently there are more than a few who appreciate the uncomplicated approach. How else could the selection of brand-new old carburetors be explained?
Of all the carburetors that have ever been produced, two of the most popular have been the Stromberg 97 and the Holley 94. Today both are being reproduced-Stromberg Carburetors, a British company, offers the 97 and Edelbrock the 94; both are cosmetically identical to the originals with some unseen mechanical improvements. A third offering, the 9Super7 from Speedway Motors is similar in appearance to a Stromberg but will not be mistaken for one by those familiar with an original. Speedway has made several changes to the original design, including manufacturing the base assembly in aluminum rather than cast iron.
All carburetors have the same basic systems: an idle system to deliver fuel below the throttle plates when they are almost completely closed with the air/fuel ratio controlled by needle valves; a main system that delivers fuel to the venturi when the throttle plates open past idle; a transfer system that supplies fuel as the throttle plates open and the carburetor goes from idle system to main; a power system that provides a richer air/fuel ratio when the engine is under load; an accelerator pump to add fuel and prevent stumbling when the throttle is opened suddenly; a float, needle, and seat to control the fuel level in the bowl. Stromberg 97 and Holley 94 carburetors have these systems, but there are subtle differences in how they are configured. Let’s take a look at the two designs individually and then compare them.
Stromberg produced carburetors for a variety of automobile manufacturers but the versions that most hot rodders are familiar with first appeared as the Model 40 in 1934 on 85hp Ford Flatheads; the model 48 was introduced on V-8s in 1935 (the preceding were both rated at 170 cfm); and from 1936 to early 1938, 97s were installed on Fords (155 cfm). The smaller-model 81s (125 cfm) were used on the V-8/60s while the larger LZs (160 cfm) were found on the Lincoln V-12s. In addition to those factory-installed carburetors, what were known as Type I Stromberg 97s were manufactured by Bendix in South Bend, Indiana, as replacements for Holley 94s; most of these have the 97 logo. Replacement versions, designated the Type II, were manufactured by Bendix in Elmyra, New York, and have a 1-1 logo.
Holley 94s are often mistaken for Strombergs even though there are some obvious differences. Used as original equipment by Ford from 1938-57 and sold by parts stores as replacement carburetors 94s have always been more plentiful than 97 and as a result less expensive. Like many things that Henry Ford was involved in, the Holley 94 had an interesting beginning.
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.
As a result, carburetors produced for Ford in 1938 are labeled Chandler-Groves, those made by Holley may have the Ford script on the float bowl while some later-model versions have a 94 cast into the bowl. There are also replacement carburetors.
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).
Seems that the MyRideisMe.com Bonneville experience never runs out of steam. Hanging out at the Nugget one evening, we bumped into Clive from Stromberg Carburetors. After a lengthy BS session, the conversation turned to carb tech. And to cut a long story short, we asked him to contribute to our ongoing “5 Things” series. Alright, so 5 turned out to be 6 – or as the English say, ‘half a dozen’. Here’s what he had to say:
1. Stromberg Carbs Run Better With The Chokes Left In
We’ve all seen those pics at Bonneville with 97 chokes removed and the kicker linkages brazed onto the base casting. It should make sense. No choke means more air space means more cfm. And you’d be quite correct, too.
Extensive 97 flow tests carried out this year by acknowledged race carb expert Norm Schenck showed that the carb did indeed pick up a little cfm without the choke plate installed. So all those Bonneville racers were right, after all? Well, yes and no. Salt Racers are only interested in WOT. On the street it’s a different matter.
Stromberg authority Jere Jobe told that 97s run better with the chokes in, so we suspected what Norm’s tests would show. Only we forgot to tell him the full story. Here’s what he said:
“I retested the signal curve with the choke butterfly and shaft removed, with somewhat disappointing results. The signal was unstable at most of the test CFM’s, and taking the average signal at each CFM to figure the signal curve showed a much less manageable curve than with the choke parts installed. My conclusion is that the choke butterfly serves as an airflow straightening “vane” that directs the airflow to the area of the boosters with reduced turbulence. Even though the choke parts cause a reduction in flow, it is not a good trade to lose good fuel metering for that CFM gain.”
So there you have it. The same story from two very qualified horse’s mouths.
By the way, if you want to keep your choke plates fixed open, try our Choke Lock Detent kit (Stromberg Part 9537K-L), which replaces the usual round-tipped detent pin in the airhorn to lock the choke plate open.
2. Bigger Stromberg Power Valves Have Smaller Numbers
Stromberg main jets are easy. What you see is what you get. Stock Genuine 97s come with 45s which means 0.045inch. Power by-pass valves (PV) – the ones underneath the accelerator pump — use the old engineering Number and Letter Drill system, devised as a way to fill in the gaps between the 1/64th sizes. And to complicate matters, the bigger the number, the smaller the drill!
And to complicate things even further, changing your PV by one number does not always mean the same change in jet size! We offer everything from #72 up to #60 (note that I said ‘up to’). The #72 is 0.025inch, #71 is 0.026, but #70 is 0.028 (a two thou’ jump), then #69 is 0.292 (WTF!) . The gap between #66 (0.033) and #65 is also 0.002inch before it returns to 1 thou’ per size right up to #57. We didn’t make the rules! But it pays to remember this when you’re trying to rejet.
And while we’re on the subject, remember that the PV only starts to affect the fuel ratio at just after 50% throttle. And when you swap them, cut a slot in the centre of a wide blade screwdriver so you don’t
3. Set The Stromberg Float Dry
The float in a Stromberg 97 (and 48, 81, etc.) is supposed to be set so the fuel level (not the float itself) is 15/32 inch (plus or minus 1/32) below the top edge of the casting without a gasket. But to be honest, that’s easier said than done, especially with the engine running and a cigarette on the go.
So for increased customer safety, our Premium Service Kits (9590K-97 and 9590k-81) now recommend that the float is set ‘dry’, as we do at the factory. Rather than a float gauge, our kits now include an extra leaflet about setting the float level. To download a copy, click here. Basically, just get the float so it sits level in the bowl when the inlet valve is shut.
All new Genuine 97 floats are pre-set at the factory, but if you’re rebuilding, you adjust the front ‘tang’ of the hinge to push it nearer or further from the inlet valve. If (and only if !) the carb is empty of gas, hold the bowl section upside down so it closes the valve by its own weight, then eyeball it through.
Here’s a 2013 article from the Stromberg website that I wish I’d seen earlier, I can 100% confirm the accuracy of the findings!
Will take the advice in the article in terms of the K&N element and see how it goes
From the article –
Our buddy Lez dug into his legendary vintage magazine stash for this great Street Rodder magazine tech article all about choosing the best air filters for your Stromberg 97s. Written by the highly esteemed Ron Ceridono back in 1998, with input from Stromberg expert Jere Jobe (from Vintage Carburetion North), it is, of course, just as relevant today as then. Sorry about the quality. It’s a scan of a photocopy, but if you click on the pages below, they will come up at a readable size.
While it’s well worth reading every word – hey we’ve even thrown in a free Dick Spadaro ad – if you’re looking for the ‘executive summary’, it’s this….. “if you have an air filter on your 97, make sure it’s a K&N E-3120”. Here’s why: Click the pages below to view, or ‘right-click’ this link to download the 2-page pdf. Choosing The Right Air Filter
As part of the installation of the Scalded Dog manifold and Stromberg 97 Carb my friend Austen at Ozcraft made the throttle link you can see in the pictures above from Charlie Yapp’s plan. The link bolts to the manifold, but had a habit of coming loose and if tightened too much the throttle action would be very stiff. So, the link was drilled out a bush added along with a locknut behind the link. This allows the link to turn freely meaning the action was far more acceptable.
As part of the fitting of the Scalded Dog inlet manifold and Stromberg 97 Carb the take off for the vacuum was no longer available in the same manner. The inlet manifold has a blanking plug underneath as standard. This was removed and replaced with a fuel line type fitting to create a vacuum take off of to power wiper motor
A piece of fuel pipe was attached to the fitting and mated with some vacuum pipe fed into the passenger compartment and added to the existing pipework to feed the motor
After the conversion to the Scalded Dog inlet manifold and Stromberg 97 carb there has been some slight throttle sticking issues. The majority of the issue had been cured by the snap shut device provided by Stromberg
Despite this the throttle still occasionally sticks a little due to the nature of the linkage.
A spring was needed and not one that was too heavy which would add to an already fairly stiff throttle action.
I couldn’t really find what I wanted so I decided to create something out of some small springs that I already had, plus an electrical connector to allow for some adjustment once fitted.
This worked out well and I was able to adjust the tension after fitting. You’ll notice the use of some heat shrink tube to make things look tidy.
So far so good!
One of the most popular carburetor choices used by Ford and Lincoln, as well as several other auto manufacturers, is the Stromberg two-barrel. The most desirable of these is the “97;” however, four other versions were also offered by Ford: the “L,” the “40,” the “48” and the “81.”
So what can they fit? There are a lot of aftermarket Edelbrock, Weiand and Offenhauser intake manifolds that will accommodate the 3-bolt Stromberg mounting base. Obviously, Ford flathead manifolds of the 1930s are their primary candidates. But the Slingshot manifold that was designed by Vic Edelbrock Sr. was just the beginning of intake and Stromberg configurations that have been offered over the last 60 years. Y-shaped manifolds are also available, allowing you to install two Strombergs on a single-barrel manifold. There are base plate adapters to convert a single-barrel manifold to the 3-bolt Stromberg 2-barrel and to adapt a four-barrel spread-bore manifold to accept dual 97s. Plus, there are 3 x 2 and 4 x 2, manifolds for 1953-’56 Chrysler Hemis and 1955-’86 small-block Chevys. You can even still find 6 x 2 manifolds for most Chevy engines. All of these manifolds are compatible with Strombergs as well as the Holley model 94, another 3-bolt two-barrel performance carb that was built by Holley and Chandler Grove for Ford, as an alternative to a Stromberg carburetor.
Read the rest of the article here
Stromberg Carbs are available new, information can be found here
Some time ago before my Dad passed away we had chatted about what upgrades might have been done to the coupe back in his days. He was born in 1936. Before I managed to get the parts my Dad sadly passed away.
So as a bit of a tribute I bought the following parts
Stromberg 97 Carb – from Dave O’Neil (O’Neill Vintage Ford)
Scalded Dog Manifold – from Charlie Yapp (Secrets of Speed)
Chrome Air Scoop – from Dave O’Neil (O’Neill Vintage Ford)
Facet Electric Fuel Pump – Carbuilder.com
Petrol King Fuel Pressure Regulator – Carbuilder.com
Fuel Pressure Gauge – Carbuilder.com
Braided Fuel Line – Carbuilder.com
Copper Fuel Line – Amazon
Rubber Fuel Pipe – Carbuilder.com
Various Connections and Unions
Jubilee Clips -Screwfix
Fuel Pump Relay – eBay
Rocker Switch – eBay
Parts I already had
MSD plug lead set and tool
Modern distributor cap
Wire and connectors
My friend Austen fabricated the required new throttle link rod from the dimensions provided by Charlie
First job is to remove the existing manifold and carburetor
This is a Model B carburetor fitted by a previous owner, this carb has had a brazed repair in the body which whilst a bit rough and ready worked fine.
These inlet manifold fixing bolt holes where not used with the original manifold, but are needed for the new one. These were cleaned out with a tap.
The carburetor and manifold were assembled and bolted into place
First attempt at wiring the fuel pump and the use of braided fuel line. This looked quite bad as the wiring was temporary to get home from my friends workshop. I didn’t like the look of the braided line.
Decided to go with copper fuel line with rubber termination to solve any issues with engine movement that may cause leaks.
The fuel pump and regulator fit nicely in the chassis rail, these were removed to change 90 degree elbows for a better pipe run
First attempt with copper/rubber fuel pipe as you can see the wiring is a lot tidier, you can also see the pipe run between the pump and the regulator. The wiring will be tidied and weatherproofed further. Use of the screwed connector has been chosen to make a pump change on the road easier.
This is a view from above, quite tidy but still not happy! Too much pipe run above the exhaust manifold and the carb feed pipe is not secured enough for my liking.
At this point a leak from the sediment trap was noticed, caused by the failure of the gasket
The reproduction item is made of neoprene but a horrible fit and had to be cut to fit. Bowl and trap were cleaned and then reassembled
Wasn’t happy with the throttle feel so spaced with some fibre washers, a lot better now. The throttle also stuck a little, so the joints on the rods were lubricated and Clive at Stromberg provided a nifty little solution to snap the throttle shut. This also doubled as a safety measure as per Charlie’s advice in case of linkage failure.
As you can see runs very well, starts better, warms up quicker, very happy.
More once I get a few trips under my belt with the new set up.