Holley Ultra XP 850 vs 950?

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All Holley HP carbs are rated at a different vacuum than "normal" Holleys. Kind of liek comparing head flow numbers from one bench at 15" and another at 28".Barry Grant started that back in the day. To really compare carbs you need to look a venturi diameter and throttle blade size.
The HP 1000 has the same size as the old Holly 850s-yes the contoured air horn picks up some but not that much. The "
old" 950s had 750 venturi size and 850 throttle plates.That was started many years ago my some of the carb gurus liek DaVinci and others. A friend just got another 950 HP that was basically the same venturi/throttle as the 1000HP/850DP size so not sure why it was only rated 950. Had down leg boosters and not the large annulars that can decrease cfm. He actually swapped the main body out for one with annulars and liked it better.



Also many of the carb tweaker guys do not like the new HP metering plates as they moved the idle restriction feed higher up and seems to create some transition issues for many motors.