For several issues now, you've been watching us squeeze more horsepower and torque out of an aging '65 Mustang GT with 289 4V power. During our first installment, we tried tuning tricks with our 289 to see how much power could be gained. We changed the spark plugs, curved the stock ignition, tuned the carburetor, and installed a Pertronix Ignitor retrofit. After a baseline of 128.4 hp and 193.9 lb-ft of torque, we gained 2.9 hp and 3 lb-ft of torque with simple tuning. No horsepower records there but some difference with tuning.
When we installed the Edelbrock Performer RPM manifold and 600-cfm carburetor in our second installment, then retarded the ignition timing, we gained 16.3 hp and 7.4 lb-ft of torque-not bad. From there, things began to look up.
In Part 3, we installed National Parts Depot's Turbo 211/44-inch dual exhaust system and Hedman long-tube headers for another 6 hp and approximately 10 lb-ft of torque. This gave us a total gain of 22.3 hp and 22 lb-ft of torque. Do you notice the pattern here? Horsepower and torque tend to go hand in hand with our modifications. Along with our exhaust system mods, some carburetor tuning tricks gained us yet another 8.5 hp and 9 lb-ft of torque-for a total increase of 30.1 hp and 30.8 lb-ft of twist. Again, horsepower and torque run neck and neck.
So what does all of this teach us? It teaches us that we should always think about engine modifications as a package. Merely bolting on a manifold and a carburetor won't net you those outlandish power promises you've been reading about since high school. To create power effectively, we have to tune and retune-with modifications. And we have to perform modifications as a cohesive package that works well together.