Hi,does anyone know if a 650dp and a 750dp baseplate are interchangable,just bought a 650dp on ebay and the throttle housing has excessive play,got a spare 750 baseplate i can strip down if they will fit?
cheers dave
Holley 650dp holley 750dp
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It will physically screw in place BUT, the throttle bores are larger and will not match the bores in the body. The larger butterflies will change the airflow signals that the carb uses in its metering circuits, this will result in less than optimum calibration. Big carburettor specialists in the states used to do this kind of mod for certain racing classes that limited venturi size but they did have the facilities to completely recalibrate all circuits.
Alan
Alan
Actually, if you indeed are speaking of Holley 650 double pumpers (list #s 4777, 82651, 76650, 80541, and others) and Holley 750 double pumpers (list #s 4779, 8156, 82751, 80528, and others) then yes, the baseplates will interchange between them, as all of these carbs have a throttle bore diameter of 1.6875". Confusion often comes in when one confuses the 600 cfm family of carbs with the 650s. List #4776 for example, has the same venturi diameters as the #4777 650, but with 1.5625" diameter throttle bores.
However, the following caveat should be noted:
Earlier (essentially pre-1995 production) versions of the non-HP carbs (list #4777 650cfm, #4779 750cfm) were "2-corner idle" carburetors and lack curb idle fuel discharge ports in the secondary (rear) throttle bores. Also, the baseplates of these 2-corner idle carbs have cast-in slots which -- while serving no purpose in these units -- route idle idle circuit fuel from the primary bores back to the secondary throttle bore down wells in some O.E.M. applications. If you are installing one of these "2-corner idle" baseplates on a later model 4-corner idle carburetor, you'll need to drill the curb idle down wells of the rear throttle bores to the proper depth, drill the proper size and location curb idle fuel discharge ports in these throttle bores, and also block the above-mentioned "front-to-rear" slots in a fuel-proof (no pun intended) manner. otherwise the carb will run overly-rich when accelerating from a stop at part-throttle.
Stan Justus
Stallion Racing Components
However, the following caveat should be noted:
Earlier (essentially pre-1995 production) versions of the non-HP carbs (list #4777 650cfm, #4779 750cfm) were "2-corner idle" carburetors and lack curb idle fuel discharge ports in the secondary (rear) throttle bores. Also, the baseplates of these 2-corner idle carbs have cast-in slots which -- while serving no purpose in these units -- route idle idle circuit fuel from the primary bores back to the secondary throttle bore down wells in some O.E.M. applications. If you are installing one of these "2-corner idle" baseplates on a later model 4-corner idle carburetor, you'll need to drill the curb idle down wells of the rear throttle bores to the proper depth, drill the proper size and location curb idle fuel discharge ports in these throttle bores, and also block the above-mentioned "front-to-rear" slots in a fuel-proof (no pun intended) manner. otherwise the carb will run overly-rich when accelerating from a stop at part-throttle.
Stan Justus
Stallion Racing Components
