Run No. 4 gained us 1.8 hp and lost us 2.1 lb-ft of torque with a spring swap. Softer metering rod springs allow the fuel to activate sooner to virtually eliminate the flat spot. Horsepower is up marginally while torque remained nearly the same. The loss in torque can be attributed to a warmer engine, not necessarily the spring swap.
Just for fun, we decided to uncork the headers to see if there really is a difference in power without the restriction of an exhaust system. We gained an eye-opening 9.2 hp by simply opening the headers. But check out the torque. We lost 2.5 lb-ft of torque. Why? Because the exhaust system helps the engine make torque via backpressure, which--given the right cam profile--increases cylinder pressure. Horsepower nearly always increases when we uncap the headers. Torque almost always decreases. Derek Real of Mike Morgan Motorsports tells Mustang Monthly that torque would improve with a 2-1/2- or 3-inch diameter exhaust system.
Our latest battery of dyno tests demonstrate that a lot of power gains aren't always in the components, but in the tuning. Common sense carburetor tuning by Mike Morgan Motorsports has netted the greatest gains thus far. But these power gains wouldn't have been possible without the correct combination of performance parts from Edelbrock, Hedman, and National Parts Depot. This is where "package" thinking comes in. Think package. Think tuning. Then retune.
Next month, we're going to install a set of Edelbrock Performer RPM heads with larger valves and ports to see what kind of power gains can be achieved.