Add Horsepower with a Holley HP Main-Body Swap

The Test
We figured the best way to test this was on our 466ci big-block Ford that we had on the dyno for our big-inch Ford story elsewhere in this issue using Jim Grubbs Motorsports' SuperFlow engine dyno. We have to admit that the 750-cfm carb was probably a bit small for this free-breathing Ford, so while this is still a good test, increasing the airflow potential through the carb with a cleaner main body would certainly deliver more of an advantage than you might see on an engine with less airflow and power potential. As an example, if we had used a 400hp 302 small-block Ford as our test mule, the difference in power between the two carb bodies would probably have been less.

With that said, we were impressed with the results we saw on our big-block Ford. A quick peak-to-peak horsepower evaluation revealed a minor 4hp difference--literally less than 1 percent. But once we compared the overall power curves, we saw major increases just past peak torque including a solid 14 lb-ft of torque at 4,600 and as much as 17 hp at 5,400 rpm. But the best news is the average power increase of 12 lb-ft and 10 hp across the entire test range.

To be fair to both carburetors, we did not use the air turbine to measure airflow since the particular unit JGM was using offers a slight restriction to airflow. Without the aid of cfm numbers, we looked more closely at the fuel flow and discovered that the power increases achieved by the HP conversion in the midrange could be attributed to roughly 5 percent less fuel than with the standard Holley carb. We had already increased jetting on the original 750 in order to improve power, yet the HP carb made more power with less fuel in the midrange. We'll attribute that to better mixture distribution in the engine from the HP's radiused inlet into the venturis of the carburetor. This may also have improved mixture distribution in the intake manifold as well. Either way, the HP made more power with measurably less fuel.

Test 1 was the baseline test on the Ford 460 with the PN 0-4779 750 carb, jetted to make best power. In Test 2, the only change was to the HP main body. The fatter jetting included with the HP carb was already in place so this effectively leaned out the air/fuel ratio on the HP conversion slightly.