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Most Mustang and Ford performance enthusiasts want more horsepower at the rear wheels. There are numerous ways to accomplish this, from bigger-inch stroker blocks to bolting on all sorts of high-performance goodies, like aftermarket cylinder heads, bigger cam, aluminum intake, or a host of other possibilities.
While all of these parts are great for adding horsepower, there’s a simple way to boost power if your engine is in good condition–supercharging. We know that Carroll Shelby was interested in supercharging, too, because his 1966 GT350 was offered with a Paxton supercharger as an option. The good news is that Paxton still offers a great unit specifically for early carbureted Mustangs.
With bracketry available from Paxton, it’s possible to bolt on the Paxton unit for a horsepower increase of up to 40 percent or more, depending on boost levels and other performance components on your engine. Not only will your lightweight Mustang be ready to run with cars having far larger engines, you’ll have great driveability to boot, meaning no lousy idle and fouled plugs to go along with the soggy bottom-end performance.
With a supercharger, torque is available as soon as you hit the gas. Your power will be available down low, not up in the clouds above 4,000 rpm where a mega-cam puts your power band.
The principle is exactly the same as it is for the thousands of late-model Mustangs with centrifugal superchargers. The mechanically driven supercharger pumps, or boosts, the combustion chamber with a compressed mixture, far above the normal atmospheric pressure. The principle is also the same for a turbocharger. However, a turbo is driven by exhaust gases rather than a belt. Other than that, the two devices both force-feed the engine to make it far more powerful.
Intrigued by the idea of duplicating Shelby’s supercharged GT350 application, we spoke to Paxton’s supercharging expert Bob Wyman. When we learned that a unit similar to the one offered on the 1966 GT350 was still available, we made the appointment to go out to the Paxton facility in Camarillo, California, for an installation and dyno test.
Along with the Paxton supercharger, we decided to use a specially prepared Holley four-barrel carburetor, modified to work smoothly and reliably in a supercharged application. Our project car, an original four-speed 1965 GT fastback owned by Joe Lackerdas, has an A-code 289, not a modified 289 High-Performance mill as found in a GT350, so it doesn’t have the solid-lifter cam, aluminum intake, Tri-Y headers, and other features found on Shelby’s original Cobra 289 engine. On Paxton’s chassis dynamometer, the stock 289 generated 124.1 hp at the rear wheels, similar to other 289s we’ve tested in the recent past. Remember, the old gross ratings were taken at the flywheel. Lots of power is absorbed in the drivetrain and rolling resistance.
Back on the dyno after the Paxton supercharger installation, rpm was limited to just 4,200. The stock distributor was suspect, with a loose-fitting rotor and a weak spring on the points. These problems can be easily remedied. A more powerful coil wouldn’t hurt either, and one technician speculated that perhaps the boost was blowing out the spark as the rpm climbed. Also, the factory A-code cam waves bye-bye at about 4,500 rpm anyway, so we weren’t too far off the mark.
Even at the low revs, maximum horsepower went from 124.1 to 152.5, an increase of 28.4 hp. Torque jumped from 176.5 lb-ft to 207.5 lb-ft, an improvement of 31 lb-ft overall. When you consider these numbers, be advised that Paxton technicians told us that early drivetrains can absorb up to half of the available power.
But there is more to these numbers. A closer look shows a 100 lb-ft gain at 2,000 rpm, right where it’s needed on a street car. Remember, our completely stock Mustang still has factory, log-type exhaust manifolds, 2-inch exhaust pipes with silent mufflers, and a cast-iron intake manifold. Paxton technicians told us that a prepped distributor, headers or K-code exhaust manifolds with 2-1/4-inch pipe and performance mufflers, and a good intake would be good for another 40-50 hp.
After driving his Mustang for a few days with the supercharger, Joe told us that the blower is completely silent. He also remarked that he must feather the clutch carefully because the engine wants to spin the one rear tire relentlessly. Remember, before the supercharger, Joe’s Mustang had 100 lb-ft of torque at 2,000 rpm. Now it churns out 200 lb-ft at 2,000 rpm. Joe tells us that his car pulls harder while running smoothly and quietly. Look for further upgrades on the 1965 fastback as we follow some of the suggestions made by Paxton, and we’ll keep you advised of the power increases.
|Here are the main components for the Paxton setup. At front left is the airbox that contains the carb. It’s airtight, so boost pressure has nowhere to go except down the carb and into the engine. Behind the airbox is the supercharger, or blower, mounting bracket with its adjustable idler pulley. At the back is the Paxton SN 2000 supercharger (center) and air cleaner canister (right) with its flexible hose to connect to the blower. Also shown is the special crank drive pulley and belt, the short hose to connect the blower to the airbox, and a special fuel pump. View Related Article|