Without a doubt, in recent years the evolution of performance carburetors has been revved up to the redline-with the stick in high gear. Modern high-performance carburetors have been on the market since the Holley modular-style carburetor made its debut in the late 1950s. As the lineup of carbs grew from this basic design, performance enthusiasts had just a few basic styles and sizes of carburetors to choose from. Those basic 4150 and 4160 carbs with mechanical or vacuum-operated secondaries served well for decades, covering the needs of street enthusiasts, racers, and even OEM manufacturers. While most of those original carb configurations from the '60s are still being manufactured today, there has been an explosion in choices available in the performance carburetor market.
What better way to test Holley's...
What better way to test Holley's new Street HP Carbs than running them on the chassis dyno on our Street Sweeper Chevelle's 496? These carbs are designed to be big on performance, while being easy on the budget.
Why all the carbs? As the needs of enthusiasts and racers evolved to demand ever more sophisticated carburetors, custom Holley carburetors created a sub-industry, and this sub-industry in modified carbs played a role in feeding that demand. It wasn't long ago that a carb specialty shop or end user would take a basic double-pumper carb and doll it up with all manner of modifications, with some of these mods proving more successful than others. The market reacted by filling these needs at the manufacturing level to the point that Holley now offers carburetors off-the-shelf with features and materials that make some of the old custom tricks obsolete.
Engine builders looking to maximize airflow no longer need to mill and streamline the airhorn for more flow, when the HP-Series is already cast with maximum flow in mind. The old practice of drilling the precision tuning circuits for calibration changes has been sidelined by replaceable air bleeds and calibration orifices. Carbs can be had with externally adjustable secondary linkages, four-corner idling, billet baseplates, lightweight aluminum bodies, float bowl sight glasses, slabbed-throttle shafts, annular boosters, and the list goes on. Selecting a carb is now far more involved than just picking a double pumper that's sized suitably for the combination. These days, the enthusiast must balance the level of features with the price point.
We had two of the new Holley...
We had two of the new Holley Street HP carbs available to test, PN 0-82851 at 850 cfm on the left, and PN 0-82951 at 950 cfm on the right. We had to wonder whether these lower-cost carbs could produce competitive power to one costing $150 more.
A new series of carbs just released by Holley is the Street HP line. Offered in 650-, 750-, 850-, and 950-cfm versions, these carbs incorporate many of the performance improvements an enthusiast really needs, while maximizing value. The main distinguishing feature is the high-flow HP-style main body, which provides greatly improved airflow and reduced turbulence compared to a standard main body. Up top, you'll find screw-in air bleeds for custom tuning, along with high-flowing, spun-in, downleg boosters. In contrast to the race HP-Series, the Street HP comes with the required vacuum ports to help with a street installation. Vacuum-secondary carbs come with two-corner idle mixture adjustment and a quick change vacuum diaphragm for easy secondary tuning, while double pumpers feature four-corner idle screws. What you won't find are billet and aluminum components as used on some of Holley's higher line carbs, but rather the traditional Holley zinc body in a tumble-polished finish, with conventional bowls and linkage. The carbs come wet-flowed and calibrated for street/strip performance.
When you really look at what these carbs have, you'll realize that most of what makes the HP carbs famous for performance and tuning is there, but you'll also notice while shopping that the Street HP is priced significantly lower than the higher-range carbs.
The 950-cfm carb on the right...
The 950-cfm carb on the right comes through with 1 3/4-inch throttle bores, while the 850 (left) features a 1 11/16-inch size. Both carbs come with conventional Holley linkage arrangements, and are mechanical secondary units with dual 30cc accelerator pumps.
A closer look down the bores...
A closer look down the bores shows the Holley HP-style main body, with replaceable air bleeds and downleg boosters. Four-corner idle circuits are also a part of the package in the double pumper versions.
The Street HP carbs come with...
The Street HP carbs come with traditional Holley components, including the conventional center-hung float bowls, cast zinc bodies and metering blocks, and cast-aluminum baseplates. Shunning the billet reduces the cost of the carbs without a penalty in performance.