Sweet2

Can someone tell me what the metering block #'s mean.
I have a list 3310, 780 with 5271 primary and 4519 secondary.
The info I find is that for a 1970 350 LT1 the the Holley was a 780 list 4555 and primary#6333 but the same secondary #4519.
What is the difference?

Steve - Race Eng

iTrader: (1)

The 3310 came in several variations through the years. 3310-1 all the way to 3310-7. Most of the changes were emissions related one cost related. The 3310-1 is a model 4150 with jet style metering blocks on both sides. I have no clue where you are coming up with 4555 for a list number. The later 3310-2 and newer carbs (1976 and newer) were 4160 carbs had a metering plate on the secondary side.

There is no reference for jet style metering blocks in terms of which stamped number fits which carb in any of my Holley manuals or books. Holley shows a 134-131 primary metering block used on all series of 3310 carbs. It is possible that somewhere through the years the primary metering block on your carb was replaced.

Metering blocks vary by idle channel restrictor size, idle and main air bleed sizes and a few other details. Most need tuning in these areas to work best anyway so I wouldn't worry too much about it.

Steve