Holley came out with the HP series,
to copy the BG patented scalloped entry,
billet pieces, etc.
BG's offerings were obviously so superior,
Holley had to upgrade their entire line.
they didn't have custom venturi sizes like BG,
they simply bolted an 850 baseplate, onto a 750 main body,
and called it a 950. Holley basically admitted, it was marketing hype,
by stating their 850 made more HP at WOT applications.
they also copied the BG sight windows in the fuel bowls.
https://www.motortrend.com/how-to/mo...true-hardcore/
Background
Holley introduced HP carburetors back in 2004, with new features such as removable air bleeds and a contoured main body. Those features were a significant improvement over the previuos style 4150 carburetors that existed, but over the years racers have asked for even more features. While the HP carbs do have some adjustment capability, the idle circuit and the power valve circuit are still controlled with pressed-in jets. With the advent of low cost, wide-band meters, the demand for fully adjustable metering has greatly increased. For that reason, Holley recently introduced a complete redesign of their classic 4150 series carburetors. These new carburetors, known as the aluminum Ultra HP series, are so loaded with new features that they make the previous 4150 models obsolete--not really, but you know what we mean. In the interest of keeping our readers in the know, we put one of the new Ultra HP carburetors under our microscope, and then bolted it on the dyno. Living up to the buzz, this new carburetor performed perfectly.
A True 950
There has been some confusion over the last several years about the 950HP carburetor that Holley sells. Many people assumed that since Holley calls it a 950HP, that it actually flows 950 cfm. More experienced people knew from looking at the specifications, that the 950HP used a 1.38-inch diameter venturi which is the same size venturi as the one used in the 750-cfm carburetors. As a point of reference, 850-cfm carburetors use a 1.56- inch venturi, and 650-cfm carburetors use a venturi with a diameter of 1.25 inches.
While I'm sure that the marketing guys at Holley had a good reason for introducing the 950HP and 1000HP carbs with those names, it did cause a certain amount of confusion in the marketplace. It's still common to hear someone mention that they are going to pull off their 850 carb and "step up to a 950." The ironic thing is that in many cases, the 950HP actually works better than the 850. Not because it is bigger, but because it's smaller. The smaller venturi size provides increased air velocity and a better booster signal for improved part-throttle performance. While the smaller 950HP works well on the street, for all out racing the 1.375-inch venturi size can limit the power output.
The large sight windows are visible on the sides of the bowls. Also notice