Ford Mustang Performance

In Parts 1 and 2 of our “Plan For Ponies” series, we’ve shown you what changes in induction and ignition do for performance. In Part 1, we removed the air cleaner, changed spark plugs, adjusted the timing, and installed a Pertronix Ignitor—gaining 4 hp and 5 lb-ft of torque. This demonstrated what simple engine-tuning could do. In Part 2, we gained a modest amount of power—installing an Edelbrock Performer RPM intake manifold, a 600-cfm carburetor, and a Pertronix Ignitor module.

This time, West Coast Classic Mustang of Reseda, California, will install Hedman long-tube headers. Magic Muffler of nearby Canoga Park will install a high-performance turbo 2-¼-inch dual exhaust system from National Parts Depot. Then we’re going back to Mike Morgan Motorsports to take another crack at the big drum to see what induction, ignition, and exhaust tuning has done for our Mustang.

What we’ve learned most from this series is that you must plan for power as a package. And it’s a good idea to begin with the exhaust system, not the induction and ignition as we have. We say this because we’re convinced that our stock, original Mustang GT dual exhaust system has hindered our efforts. In order for an engine to perform, it has to have good exhaust scavenging; otherwise, no amount of induction, ignition, or headwork will matter. Our high-performance Turbo 2-¼-inch exhaust system from National Parts Depot has 2-¼-inch pipes with Turbo mufflers that not only improve sound, but performance as well. Hedman long-tube headers reduce backpressure and scavenge exhaust gasses, while keeping torque in play. With aftermarket headers and larger exhaust tubing, we wonder what all this will do for performance. We’re about to find out.

We took the Mustang back to Mike Morgan Motorsports, and once again, we were disappointed with the result on the first pull. Our rejetted Edelbrock 600-cfm carburetor struggled with an ugly flat spot that was hurting torque something awful. During throttle tip-in, the 289 was gasping for a respectable air/fuel mixture that would allow it to make power. Wide-open throttle passes were made with poor results. This was no reflection on the exhaust system or Edelbrock induction system; it was an issue of proper engine tuning. We did some carburetor tuning and achieved impressive results.

Our first dyno run with Hedman headers and NPD dual exhausts was right off the street without any tuning. We gained 4.8 hp and 4.6 lb-ft of torque by improving the exhaust system. There’s room for more improvement.

Prior to Run No. 2, we adjusted the Edelbrock carburetor’s accelerator pump rod to see if we could eliminate the flat spot. We were marginally successful. The flat spot remained, indicating the need for more extensive carburetor tuning. Despite the surging, we gained 2.3 hp and 5.2 lb-ft of torque. This is due mostly to a warmer engine, not necessarily the accelerator pump adjustment. But this shows us what’s possible, given respectable engine tuning.

Using Edelbrock’s carburetor jetting kit, we tuned the main metering circuit using the pink metering rod spring. This gave us a richer fuel mixture where we needed it most: under power where an engine makes torque. This netted 5 more horsepower and 6.2 additional lb-ft of torque; not bad considering how easy this performance-tuning trick is.

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 2½- 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. In the next installment, 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.