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Testing 1-2-3
We put several multi-carb setups through a workout on dyno
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In preparation for our Ford Y-Block engine build story in the July/August 2009 issue, we discovered a great deal of conflicting information in regards to using Holley 94 series carburetors in multi-carb setups. Some believed the Holleys were a poor choice for these setups, while others proclaimed their superiority over the more commonly used Stromberg 97s. The bulk of the controversy centered on the power valves, and whether it was best to block them off on the secondary carburetors when using progressive linkage, or to leave them open.

We decided to put the Holleys though their paces and accurately test them to determine what tuning was needed to optimize their performance on our Ford 292ci Y-Block. Our test engine was overbored .060-inch and features a Clay Smith cam, Ford #113 heads, and a vintage Edelbrock 573 manifold with a set of “Marshall Since ’62” one-inch aluminum carb spacers. We wanted to test the different primary and secondary bases available through Vintage Speed, progressive linkage versus straight linkage, staggered jet sizes versus even jet sizes, and different power valve sizes and block offs.

Engine dyno testing is only one means of judging a carburetor’s performance, but it gives us the ability to monitor closely the air fuel delivery to the engine throughout the rpm range in a controlled environment with the engine under a prescribed load. This enabled us to tune our carburetors to achieve optimal performance for the engine without the risk of damaging the engine by running it in a too rich or too lean condition.

A new Player
As soon as we finalized our plans and started rebuilding several Holley cores (see Web Exclusive story ‘Rebuilding The Holley 94’), Speedway Motors released their new take on the old, familiar Stromberg 97 in a carburetor they dubbed the “9Super7.”

The 9Super7 is not the first recreation of the original Stromberg 97 design, in fact, we tested the “Stromberg 97” built by English manufacturer Stromberg Carburetor Ltd. on our earlier ‘Desoto Hemi’ build and found them superior to rebuilt originals. However, by the time we dropped $450/each for the quartet of new Strombergs and $650 for a vintage Weiand intake manifold, our wallet felt considerably lighter and left us wondering if we should just pony up a few more bucks and equip our engine with Hilborn injection.

The English built Stromberg 97 is truly a great piece in its exacting detail, recreating the original to the smallest detail while making several improvements in functionality. On the other hand, the 9Super7 from Speedway Motors lists for $299/each, and we had nearly racked up that much each into rebuilding our Holleys with all the options we wanted to test. We were skeptical of how they would perform for the price, but couldn’t resist ordering a set; after all, we were going to be on dyno anyway. There seemed to be a great deal of speculation about Speedway’s newest release, but mostly by people who had ever actually tested one or even bolted one to an engine and fired it up. So, we were anxious to get some real numbers on this budget friendly alternative.

All fired up
When dyno day finally arrived, Speedway’s 9Super7 carbs were first up to be tested. We knew from our experience with Stromberg carbs that they would be easy to tune and could be “dialed in” in a few short pulls. We pulled the carbs straight from the box and bolted them on. They came with .045-inch jets that proved to be a little stout for our application, but not so fat as to harm the engine. We reduced our jet size to .042-inch and then .040-inch to get the air/fuel ratio optimized before making our first pull on the dyno. We were impressed by the smoothness of the engine as well as the throttle response, as Clay Witt of TPIS pulled back the throttle lever. The 9super7 maintained excellent air/fuel ratios throughout the entire rpm range of our Y-Block engine. The dyno numbers rolled across the screen and yielded us 243-horsepower at 5,400 rpm, and 278 ft.-lbs. of torque at 3,500 rpm. It was a good start to the day, but we knew we’d have our work ahead of us fine-tuning the Holleys.

We began testing the Holleys by installing a set of Vintage Speed primary and secondary
bases to our Holley ECG5 carbs with 1 1/16-inch venturis. The secondary base kit from Vintage Speed came with everything we needed to get the job done, including gaskets, #4.5 power valve, power valve block off plates and tri-carb stainless steel progressive linkage. After a few short pulls, we finally settled on#68 jets in the primary carb and #58 jets in the secondary carbs. This combination gave us excellent air/fuel ratios throughout the rpm range as well as idle and part throttle situations, and delivered 252-horsepower at 5,400 rpm, and 284 ft.-lbs. of torque at 3,800 rpm.

Next, we tested the same carb and jet setup but changed out the bases in favor of the original ECG5 bases, which include a spark valve at the back of the carb base. All three bases included #4.5 power valves. We suspected our combination would be excessively rich with the addition of two more power valves, but soon realized we were closer than we would have guessed. We reduced the primary carb jets to #66 and left the secondary jets at #58. This combination yielded 253-horsepower at 5,400 rpm, and 277 ft.-lbs. at 3,500 rpm.

In conclusion

We left TPIS with a fist full of dyno sheets that would keep us occupied for days to come. What struck us first was how well the 9super7 performed right out of the box and how little adjustment was necessary to tune it to our engine. Comparing the overall engine performance between the 9super7s and the Holleys would be unfair, as the flow rating of a Stromberg 97 styled carb is only 155 cfm with its 97/100-inch venturi, while the Holley ECG5 venturi size of 1 1/16-inch boasts a 185 cfm flow rating. Considering the large difference in venturi size, the 9super7 held its own against the larger Holleys up to 4,500 rpm when the advantage of greater flow kicked in.

When comparing the two Holley configurations we tested, we were surprised to see both a torque increase when equipped with the Vintage Speed bases and a modest increase in horsepower with the original Holley bases. In either case, we concluded both would make a solid street combination, though the final word would likely have to come from behind the wheel. While dyno testing will ensure we are within reach of our goal without sacrificing our engine along the way, it’s no substitute for real world drive testing.

Marshall Since ’62

Outcast Kustoms
(651) 492-9565

Speedway Motors
(800) 979-0122

TPIS-TPI Specialties
(952) 448-7988

Vintage Speed
(772) 778-0809


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