whisperer
Member
This is just my opinion, but Holley 4150/4160s are very much misunderstood. What is the List Number on your 4150 650 DP? There are a few oddballs out there but the 650 and 600s typically share a common main body, both of which have a 1-1/4 primary and 1-5/16 secondary venturi. The main difference in the carbs is the base plates, the 600s having 1-9/16 throttle plates on primary and secondary, and the 650s having 1-11/16 on primary and secondary. You can make one into the other by changing the base plates so instead of selling your 650 and buying a 600 just buy a 600DP base plate if you are so inclined. That said, changing the size of the base plates will have little effect until you run out of CFM capability at top end. Changing the size of the venturi will indeed have a strong effect on lower RPM performance. A smaller venturi will pull harder at low RPMs but will run out of capability at higher RPMs, and visa-versa.
The rest is just tuning that you will have to do with any carb. Something to remember is that a smaller carb (venturi) takes a smaller set of main jets to achieve the same mixture on a particular engine. It doesn't mean you use less fuel, it just means that the CFM requirement of the engine is the same at a given RPM, and the velocity through a smaller venturi is higher and "pulls harder" on the fuel through the main jets. (Smaller venturi, higher vacuum signal).
It's very important on a 4150/4160 to get the power valve sized correctly for the engine. On a near-stock 289 you will have plenty of fuel on a DPDF 600/650 4150 as long as the pump shots are timed correctly. I'd start with 125-65 or possibly 125-50. These will operate when the vacuum signal drops BELOW 6.5 in. or 5.0 in. respectively. (125-65 = 6.5 in., 125-50 = 5 in. and so on.)
If it was mine I would just bolt on the 650 with a 125-50 power valve and probably install down-leg boosters in the primaries and install 65s and 75s main jets to start. Then it's just tuning from there.........
The rest is just tuning that you will have to do with any carb. Something to remember is that a smaller carb (venturi) takes a smaller set of main jets to achieve the same mixture on a particular engine. It doesn't mean you use less fuel, it just means that the CFM requirement of the engine is the same at a given RPM, and the velocity through a smaller venturi is higher and "pulls harder" on the fuel through the main jets. (Smaller venturi, higher vacuum signal).
It's very important on a 4150/4160 to get the power valve sized correctly for the engine. On a near-stock 289 you will have plenty of fuel on a DPDF 600/650 4150 as long as the pump shots are timed correctly. I'd start with 125-65 or possibly 125-50. These will operate when the vacuum signal drops BELOW 6.5 in. or 5.0 in. respectively. (125-65 = 6.5 in., 125-50 = 5 in. and so on.)
If it was mine I would just bolt on the 650 with a 125-50 power valve and probably install down-leg boosters in the primaries and install 65s and 75s main jets to start. Then it's just tuning from there.........