Stromberg BIG97 dyno thrash

Norm Schenck at Competition Fuel Systems has been dyno testing Stromberg 97 and BIG97 carburetors for us for year. In fact he had a major hand in developing the BIG97 from scratch.

We set up a dedicated dyno motor at Norm’s facility in Vassar, Michigan and we’ve been watching intently as horsepower has grown with small tweaks to the carburetion and heads. This set up is with the cast iron vortec heads, that Norm ported himself. We have a set of AFR CNC ported heads waiting in the wings and they would probably make more power, but Norm suspects that the limitations of the Edelbrock tri-power intake would not have allowed for much more flow than was achieved with the vortec heads.

Want to know the numbers? This is a GM 330 horse crate motor and the best we got this time (by taking off the mufflers) was 404 ft-lbs of torque at 4300rpm and 386HP at 5400rpm. We still made over 400/380 with the mufflers on. This was on 89 octane gas with top end A/F ratios all in the 13s ! The dyno can now read separate A/F ratios per cylinder.

What this motor will do once someone (ie us) develops a new intake for the BIG97s is anyone’s guess. But it will be impressive, you can be sure of that…

Chrome Chevy 97 fuel line


Back in the summer we launched our first Big Bore 97 fuel line – 9146-BIG for Small Block Chevy intakes – backed by a range of new fittings to make installation easy. You can click the links to read more about them. This time, we’re announcing that all of these – and more – are now available in traditional chrome or hand-polished finish to complement your chrome 97s.

We’ve added pictures of the whole range below, with the new part numbers so you know what to order. All you need to remember is that the fuel block has 1/4NPT threads at both ends so you can input your fuel line (solid or hose) from front or back, and either plug the other end off or add a fuel pressure gauge.

This 97 fuel line is designed for use with our BIG 97 carburetors which have special S-jet inlet valves to accept the 5/16in line (regular 97s need 1/4in line). To use the new 9146-BIG-P with regular 97s you MUST swap the S-jets out for 9564K-BIG-C chrome S-jets. The new 9146-BIG-P line comes with special chromed Ford Nut style compression fittings to fit the bigger line and S-jet, but they are also available separately as kit 9081K-BIG-C in case you want to build your own polished 5/16in fuel lines.

Finally, while we’re looking at new polished fuel fittings, now’s a good time to mention fully polished versions of our banjo spacers (9086K-P) and ‘fuel gauge banjos’ (9082K-G-P and 9083K-G-P).

Our new Big Bore 97 fuel line and fittings are part of the Stromberg Linkage & Fuel Delivery range, available from a network of Genuine Stromberg dealers worldwide. As always, full instructions are included with the fuel line and further help is available via the Stromberg Tech Center at .


Let’s build a Stromberg 97 3×2

Chevy 3x2The basis for this how-to comes from some posts we made to a Jalopy Journal HAMB thread, “Let’s build a Stromberg 97 3×2“. We felt it was good idea to give our own view on the best way to set your 97s up on a Chevy small block motor. Everyone is entitled to their own opinions, of course, and we respect that. These are just ours. This does not apply to the new BIG97s, either. Please see our separate How-To articles on the BIG97 tri-power.

Primary/Secondary…It is our belief that you cannot regard three Stromberg 97s in the same way as an old muscle-car era, factory Rochester tri-power. They are completely different carburetors. It is far wiser to ask how the 97 can work best for your particular application. Back in the day, people mostly used a direct linkage for 97s on the new Chevy 265 and 283 motors, with all three carbs kept the same, and yes, you can set the carbs up to work like that with great results. What we tend to do now, though, is use a progressive linkage  – also with all three carbs the same – rather than the traditional idea of one good primary and two ‘dumb’ secondary carbs with giant main jets, but no power valves or idle circuits. It’s a sort of half-way house solution. We still call them primaries and secondaries, but only in terms of where they sit and which open first.

Looking at your 3×2 progressive then…We recommend you leave all three carbs with WORKING idle circuits in all three so all of the cylinders get even fuel distribution at idle and up the rev range (idle circuits stay on for long than you might think).. On those dual-plane Chevy 3×2 intakes, the center carb can supply all eight cylinders, but they’re pretty old designs, unchanged since the 1950’s, so the better access you can give all cylinders to even fuel/air distribution the better. What you don’t need is lean end cylinders. And by the way, leave all the chokes in as 97s need them to ensure reliable vacuum signal at the emulsion tube tips. You can lock them open with our 9537K-L kits if you need (all or just the outer two). And aim for 2.5psi regulated fuel pressure. You can go lower but not much higher.

Using this exact set-up, we tested a hot 355inch Chevy motor back in late 2010 in Arizona (around 2000ft elevation) on a new Edelbrock 3×2 intake and it made 345hp at around 5000rpm with better fuel efficiency than a Holley 600 4bbl. Those intakes max out at 5000rpm. We found it revved to about 5700 but the power and torque was flat after 5K. Max torque was about 380ft-lbs. We were testing something else at the time so at the end of the session we literally used three 97 carbs out of the box with stock 0.045 jetting and number 65 power valves, and the air/fuel ratio was pretty good from idle to 5K. We did find, however, that you could disconnect the outer carb accelerator pumps and it made almost no difference. You didn’t need the outer pumps (squirters) or the extra top end enrichment from the outer carb power valves either (they come in when the accel pumps hits the pin on the top of the power valve at about half throttle).

Some people have talked about filling the outer carb PV holes with epoxy. If you do this, and leave the accelerator pumps linked, you will get some hydraulic pressure in the pump well (which could damage the linkage), even with the little relief valve in the bottom of the pump. Plus you pretty much wreck the carb for alternative use. It’s easier to just disconnect the outer carb pump link rods, though we have developed a ‘dummy’ pump for use in a future project so you can keep the look of your pump and pump link. We did not spend a lot of time on this dyno test and maybe we could have adjusted the tune to keep all three PVs and pumps working. I expect we’ll test this set again soon, so I’ll report what happened on a different 330hp GM Performance crate motor we have.

CFM Requirement…This is one of the main reasons why some people believe that three 97s are not enough for a modern 350inch small block Chevy. But it’s too easy to get hung up on cfm requirements. The important thing to remember is that maximum cfm is only important at max revs. The traditional math for cfm requirement might say that three 97s at 162cfm each is not enough air for a 350 inch Chevy, though evidence on the dyno and the road disagrees. And we suspect that’s because we all overestimate the volumetric efficiency of our engines. Remember we said that the 355inch dyno results stopped at 5000rpm? That wasn’t the carbs. It was the manifold. At idle your Chev could run on a lawnmower carb because the basic requirement is cylinder volume x revs. Low revs = low cfm requirement. And when you get higher up the rpm chart, volumetric efficiency pays a larger part in governing what you really need. We can only quote the dyno test above and remind you that we have many customers running this system including one local buddy who leaves black tyre lines at every local stop light. 345hp in a lightweight ’32 Ford can get pretty scary! And they really do rev up quick with the progressive linkages.

Balance/Tuning…Set all three carbs on the manifold with no linkage at idle. Get a vacuum gauge and balance all three carbs so each is set the same and contributing the same air/fuel mix to the overall engine. Aim for the maximum vacuum from all three carbs. You can adjust them using the throttle stop screws on the side of the carbs, and the idle mixture screws on the bases to keep it smooth and not lumpy. It’s fiddly and you have to go around and around adjusting. There was a great post on the HAMB about carb balancing a few years ago if you can find it. But you should get a smooth idle at the rpm you want – using all three carbs.

Then you can fix the linkage making sure that it does not disturb the idle balance you have already. You can read how to set the linkage up on our tech center –…nkage-Inst.pdf

With a progressive linkage, your outer carbs sit there (feeding a little in through the idle ports) until you hit about half throttle, at which point your centre carb will come onto the power valve and start enrichening the mixture just as the outer carbs start opening, adding more air and gas. The main jets start up literally the moment you open a 97, so they’re good to go straight away as the signal is very accurate. It’s that smooth progression that makes them work so well. On a Chevy, start them out of the box and then read the plugs or get the gas analysed. You won’t be far off at 0.045 main jets and number 65 PVs (the ‘out of the box’ setting). And try it with the outer accel pump links disabled. Each application will differ slightly with local gas, elevation, cam etc.

Distributor vacuum…The 97 provides no ported vacuum for a distributor advance. We recommend an all-mechanical distributor because we have had customers connect the distributor to the manifold and it doesn’t like it. It won’t idle and throws out black smoke because the distributor is fully advanced at idle. We have seen vacuum taken from the rear plug on the 97 base, but Norm Schenck, our consultant at Competition Fuel Systems in AZ says, “we need the vacuum advance only at light load/part throttle conditions (cruising), and none at idle or full throttle. Only a port on the front of the throttle bore at the same height as the transition fuel port accomplishes this”. We are working on a new base to achieve this, right now.

Linkage and fuel lines….Stromberg offers a wide range of fuel delivery parts for this application, from straight brass hose ends to banjos – including some with a mechanical fuel pressure gauge port in the end. Please note that to use banjos with a progressive linkage you also need our banjo spacers to move the fuel line away from the center carburetor linkage lever. For the Chevy, our 9246PRO kit is well proven and comes with two torsion carb return springs. If you want to use a throttle cable, our 9136K Cable Throttle Bracket is designed to hook you right up. We also offer a 9246PRO-KD version that can pull your auto trans kickdown cable.

Got any further questions? Email us any time at

1940 Chevrolet D-Gasser – Stromberg equipped!

Beaty 40 chev

They don’t come more original – nor much cooler than this baby. Move along please for Texan Chet Beaty’s 1940 Chevrolet D-Gasser, running an original Wayne-equipped 1952 GMC 302 with 5 – count ’em – Stromberg 97 carburetors along with everything else right from that period. A Spalding cam, Vertex distributor, Sun Tacho, 1937 LaSalle floor shift tranny and a 1951 rear end. Down to the window decals, this car is a genuine 1958-built car and you know what? He fully intends to keep it that way. Now, if we can just fix those leaky throttle shafts…

STOP PRESS! Chet just fitted five brand new 97s from Stromberg Carburetor, keeping the car authentic and Genuine! Just the same but Better than ever…






Stromberg linkages now with kickdown!

DSC_8943Got a Chevy or a Ford with three 97s and an auto box? You need our new 9136K Cable Throttle Bracket plus our new Stromberg TwoStep progressive carburetor linkage with auto-trans kickdown capability.

What’s the secret? Our totally new center (primary) carburetor lever, which extends below the throttle shaft center line to pull the kickdown cable at a point set by the owner. The ‘kickdown’ end has a ¼”UNF thread, which accepts the special fixing common to most hot rod aftermarket auto-trans kickdown cable kits.

Linkages with the new kickdown capability simply add a KD suffix to the regular part number, so the 9246PRO 3×2 kit for small block Chevy intakes becomes 9246PRO-KD with kickdown. For small block Ford, choose 9253PRO-KD. Chrome versions are also available. All KD linkages come with two of our Snapback torsion-type throttle return springs, by the way. We have shown the traditional springs in our ‘assembly’ pictures to highlight a typical conversion from a Lokar-equipped 4-barrel carb to three 97s.

To be honest, kickdown is an issue we rarely encounter with flathead Ford applications, but with more hot rodders choosing a 97 tripower for their small block Chevy or Ford, our new ‘kick-down compatible’ progressive linkage, coupled with our new 9136K Cable Throttle Bracket, is a real problem solver. Just one note, if you have one of the more modern auto-transmissions like the 700R4, for example, please seek professional advice about the TV cable requirements. It’s not as simple as with an old-style Turbo 350, for example, as the rate of cable ‘pull’ is as important as the distance pulled. We are looking at special solutions, but they’re not ready right now.

Here’s the full KD range, available from stock. The new center carb lever (Part No: 9096K-KD) is also available separately, complete with swivel and clamping screw. If you need something else, please ask!

9246PRO-KD – 5-1/2″ carb centers – typical small block Chevy 3×2

9251PRO-KD – 4-7/8″ carb centers – Offy Y-block & Cad 3×2

9253PRO-KD – 4-3/4″ carb centers – Edelbrock small block Ford 3×2

All these new Stromberg linkages are on the website under the Linkage & Fuel Delivery menu. Prices are the same as the regular linkages. And as ever, full installation instructions and ‘how-to’ help are also available at the Stromberg Tech Center at