Conclusion
The Holley Street Avenger carburetors are designed to be calibrated correctly straight out of the box if they're used for their intended application (and there's a chart on the Holley website to help determine this), though admittedly the 670cfm carburetor is slightly large for a 305ci engine and we'd probably have been better off starting with a 570, but then we probably wouldn't have been able to improve on the stock settings! Given the engine's stock state of tune and its stock cam, it wasn't going to respond to tuning much beyond what we did, but we did pick up 4 lb-ft of torque and almost three horsepower by installing smaller secondary jets. The motor also ran slightly leaner above 3,500 rpm, though admittedly its cruising speed in third gear is around 2,300 rpm, so it's a somewhat moot point on this vehicle.
Out on the road after the test however, the pickup was more responsive, with better acceleration, though I haven't driven it far enough yet to report any change in gas mileage. While the FAST meter is of more use on a performance engine, you can see how it is useful for tuning fuel delivery. 14 parts of air to fuel is where you'd expect to see a carbureted engine in the lower rpm range, so we were in the right area to start with, and managed to improve the ratio at higher revs while increasing both peak horsepower and torque. Sounds like a successful morning's work to us!
 The Holley has a square flange...  The Holley has a square flange bolt pattern, meaning we had to move our carburetor studs to the outer holes. Two nuts locked together make it easier to remove stubborn studs, using the wrench on the lower nut. Beats mangling them with Vice-Grips! |  We used the fuel lines that...  We used the fuel lines that were supplied with the carburetor to hook up the fuel supply as this was the easiest way to connect to our existing gas line. The electric choke wires were in the same place and the Heim-jointed throttle linkage also needed no modification. The only change we had to make was to lengthen the vacuum line to the PCV. |  Though Holley supplies a base...  Though Holley supplies a base gasket we had to use a thicker insulated gasket to raise the Street Avenger enough to enable the fast idle set screw to clear the intake manifold at wide-open throttle. Weiand manifolds have a groove machined into them to eliminate this problem, but on stock intakes and some other aftermarket manifolds, including the Edelbrock Performer, there can be a slight clearance issue. |
 With the sensors installed...  With the sensors installed we strapped the pickup to the dyno to simulate a real world road test (this also allowed us to get some horsepower and torque figures to illustrate the results of the tests). This offered all the benefits of a test with the drivetrain under load at cruise speed without actually having to drive the truck at a steady speed on a long stretch of road. Call us lazy but it enabled more data to be collected in less time, though we should stress the FAST kit is designed for mobile use. The FAST meter is ideal for tuning to achieve the optimum air/fuel ratio, but it doesn't give horsepower figures. | | |