3 Barrel Holley carb and conversion kit
Complete modified 600 carb, it is now a 450 CFM 3bbl.
Or: Instructions and a special plug to convert your Holley Vacuum Secondary Carb to a 3 BBL for improved fuel mileage and response. To be used with a OPEN plenum intake design. Like is used on Chevy inline 6 intakes.
A 600 CFM converts to 450CFM Good for 250
A 750CFM converts to 562CFM Good for Hot 250 and 292
If a complete carb is ordered, a new Aluminum Holley 600 or 750 is used and converted, a adjustable vacuum can and spring kit are also added to carb.
In this case 255 inline Chevy 6 cylinder. The modded carb is equal to 450 CFM and performs flawlessly. When in normal cruise RPM's, the carb runs one 1 primary throttle blade and when power is needed, both secondaries will then open providing the CFM's for power. As shown, this carb delivered almost 21 MPG going on highways ranging from 55-75 mph.
I know you are asking yourself, why convert it to a 3 bbl when the 600 4 bbl should also perform well. When running both primary's at cruise speed, the throttle position is not very far open and you are running on the idle circuits on a small engine. This is a inefficient fuel / air mixing circuit. When running a single primary, the blade will be opened further, promoting better fuel/ air mixing with the venturi .
Cam is a same as my Thrifty cam at www.12bolt.com . I sell a instruction sheet and the special plug to modify either a 600 or 750 Holley. They take different plugs.
The secondary opening rate is adjustable on these carbs to tailor it to your engine.