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Holley vs. Edelbrock
Tom Herman; via CarCraft.com: It seems a Holley carb is worth 10 to 20 hp over a similar sized Edelbrock. My question is why?

Jeff Smith: I'm not sure what your question bases its assumption on, but there are a few details about both carbs worth considering. When it comes to the smaller four-barrel carburetors, such as the 600-cfm fuel mixers, our experience indicates there is very little difference in terms of power potential. The Edelbrock Performer carburetors are based on the older Carter AVS (air valve secondary) series of carbs. These carbs use a mechanical-secondary actuation and then control secondary airflow with a spring-loaded secondary air valve door that opens as primary airflow velocity increases, feeding air and fuel to the engine as needed. These carbs come in 500-, 600-, and 750-cfm sizes. The Edelbrock carbs seem to enjoy a reputation for running well right out of the box. For performance applications under 450 hp, the 750-cfm Performer or EPS 800-cfm carbs would be a good choice. Above 500 hp, these larger-cfm carbs may be limited based on maximum fuel flow because of a single fuel inlet and needle and seat compared with a dual-inlet Holley of the same cfm rating.

Let's assume for a moment that we have a 400hp single-four-barrel small-block Ford and we've decided to use a 600-cfm carburetor. Let's say we've chosen to compare a Holley 0-1850 ($253.95 Summit Racing) vacuum-secondary carb with an Edelbrock PN 1405 ($273.95 Summit Racing). The prices are very similar so that's not really an issue. From a power standpoint, the difficulty in comparing these carburetors is that they are generic performance carburetors. As such, they will probably be very close in terms of horsepower, but to get maximum benefit we would need to tune them for the engine in question. The best way to do that would be with a wide-band air/fuel (A/F) ratio meter to ensure the ratio is somewhere around 12.5:1 to 12.8:1 at wide-open throttle (WOT) and a leaner 13.5:1 to 14.7:1 at part throttle for good throttle response and driveability. More than likely, these carbs will be close but may require some tuning with jetting, power valves, or idle-mixture adjustments to achieve these numbers. If we were to put both carbs on the engine on the dyno, our opinion is that you would be hard-pressed to see more than a 5hp difference between the two. Frankly, you would need a very repeatable bracket car to see even that small a difference, and even then, the difference would be measured in hundredths of a second.

Both carbs have tuning advantages and disadvantages. There's no simple way to change the secondary opening rate for the Edelbrock, but on the Holley you can swap secondary diaphragm springs (the Thunder Series Edelbrock carbs are more expensive but do offer secondary adjustment). Primary metering adjustment for the Edelbrock is really easy. It uses a combination of metering rods and jets, and you can access the primary metering rods from the outside of the carb with a simple Torx screwdriver. The Holley requires you to drain and remove the fuel bowl to change jets. The same is true for secondary metering adjustments on the Edelbrock because the top needs to be removed to access the secondary jets. The latest version of the 0-1850C Holley has also eliminated the external float adjustment, which means both carbs require disassembly to adjust the float. This might be a long answer to a very short question, but in my opinion there would be a very small, if any, performance advantage of one carb over the other. As the saying goes, "You pays your money, and you takes your pick."

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