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8 Muscle Mustangs Dynojet Showdown
We Test Eight Mustang Musclecars On The Dynojet
1969 Mach 1 428 CJ Automatic
Actual Rear Wheel: 213 hp/266 lb-ft
Estimated at Flywheel: 266 hp/332 lb-ft
Factory Rating: 335 hp/440 lb-ft
When Chris Sackett’s 1969 Mach 1 rolled onto the Dynojet rollers, we knew we were stepping up to some serious big-block horsepower and torque potential. The Mach 1’s 428 Cobra Jet ram-air rating of 335 net hp has led the street-wise to accuse Ford of sandbagging the numbers for drag racing purposes. We figured we’d find out.
Chris, from Bath, Michigan, purchased the blue Mach 1 a year ago, supposedly with about 10,000 miles on a fresh engine rebuild. During the first three Dynojet pulls, the exhaust dumped a lot of dark smoke, indicating an overly rich mixture. Removing the air cleaner for a look revealed an Autolite service replacement four-barrel, a 480-cfm 4300 version, instead of the correct 715-cfm Holley. According to Paul, the secondaries also were opening too soon, well before the engine was ready for the additional fuel, leading to the rich conditions and only 192 rear-wheel hp. Making a pull without the shaker-scooped air cleaner helped, providing the best run at 213 hp. Factoring a 25-percent power loss through the C6 automatic, the engine was putting out 266 hp at the flywheel, way off Ford's 335 rating.
Paul noted an incorrect distributor, noticed during the carburetor inspection, may also have been a factor in the car's lackluster performance. Although it looked factory, Paul explained that non-CJ Ford distributor probably had an incorrect advance curve for optimum Cobra Jet performance.
1970 Boss 302 Four-Speed
Actual Rear Wheel: 179 hp/209 lb-ft
Estimated at Flywheel: 209 hp/245 lb-ft
Factory Rating: 290 hp/290 lb-ft
We expected a better showing from John Niffin’s 1970 Boss 302. A mostly original, 45,000-mile car, the Medium Lime Boss has belonged to John since 1976. The original engine expired at 18,000 miles--the result of the Boss 302’s piston skirt problem, no doubt--and was rebuilt to factory specs. However, John, who lives in White Lake, Michigan, added a Motorcraft electronic ignition to eliminate the hassle of keeping the factory dual points adjusted.
The Boss sounded stout on the Dynojet, but the first three pulls generated a best of just 169 rear-wheel horsepower. A quick inspection under the hood revealed that the manual choke was partially closed and the initial timing was set at 19 degrees, so Paul quickly shoved in the choke handle and reset the timing to a more realistic 14 degrees. The simple changes resulted in a 10hp jump, up to 179, at an uncharacteristically low 4,700 rpm on an engine recognized for its high-rpm power.
Afterward, Paul noted that electronic ignitions advance the timing slower than point ignitions, and they also dial in up to 45 degrees of advance at higher rpm, which is too much for vintage cars that require only 36-38 degrees. Paul felt that a simple ignition change, back to the original dual-point distributor, would restore the factory performance in John's Boss 302. As a side-note comparison to the Windsor-head K-GTs, which developed their torque peaks between 1,800 and 2,300 rpm, the Boss 302 didn't reach its peak torque, as expected with the large-valve, Cleveland-style heads, until almost 4,000 rpm.