Eric English
February 17, 2010

This is a tough engine to separate from the car it came in-primarily the Boss 302 Mustang-as it was as magical as the engine itself. The Boss 302 Mustang was purpose-built as a homologation effort to legalize the high-winding small-block for Trans-Am racing, and yet it turned into one of the most successful Ford muscle cars of all time-with some 8,600 total Mustang units built. Ultimate power wasn't the name of the game here, rather max power and reliability for the given 5.0 liters of displacement per SCCA rules. To that end, the Boss started with a specific four-bolt main bearing block and forged steel crank-the only production Windsor small-blocks ever to use such. Solid lifters teamed with massive port and valve dimensions to make the 302 a screamer at high rpms, while a high-rise aluminum intake and 780cfm Holley directed the fuel mix. For the street, the '69 production 2.23/1.71-inch valve sizes were soon deemed just too big, and were revised for 1970 to 2.19/1.71-inch.

Our sister publication, Hot Rod, just ran an enlightening story that quantified what Ford fans have known for years. With the dyno gurus at Westech Performance, Hot Rod orchestrated a face off between a '69 Z/28 "DZ302," and a '69 Boss 302. Equalized with like-dimensioned 750 Holleys and 1 3/4-inch headers, the Boss peaked at 372 horsepower at 6,800 rpm compared to the Chevy's 356 at 6,700. Peak torque favored the Chevy by a small margin, 333 lb-ft at 4,400 rpm vs. 325 at 4,200, but the Boss surprisingly produced more torque down at 3,000 rpm, so there seemed plenty of give and take in the torque department. Of particular note, the test was performed with factory spec cams and compression-the Chevy's being a bit more aggressive in both departments. In the free wheeling world of Trans-Am racing where cam and compression was wide open, you can imagine the power differences would be magnified. This was proven out in a very competitive debut year in 1969 and the Trans-Am championship in 1970.

Boss 351
Is it any surprise we've included all three Boss engines in our top ten? The Boss 351 may be slightly disadvantaged on the surface due to just one year of production and no factory supported race effort, and yet it stands on its own as perhaps the best performer of all time in the category of small-block V-8. It had the goods from top to bottom-decent cubic inches from a four-bolt block, those awesome flowing four-barrel Cleveland heads, 11:1 compression, and more.

Few laments surround the 351-although the Boss 302's Holley 780 would've been nice, the Autolite 4300D carb did flow an adequate 750 cfm. Maybe the biggest knock on the Boss 351 wasn't the engine itself, rather that it was installed in the heaviest Mustang platform of the vintage era. Just think what the thing would've done in a '67! Nevertheless, Boss 351 Mustangs vie for the title of quickest classic Mustang, with period magazine tests even scoring a couple high 13-second performances.

Here's one more item to consider that helps cement the Boss 351 in our lineup. This is our only engine that is fully representative of the Cleveland architecture, which clearly has a rich performance tradition in Ford history. By the mid '70s, the 351 Cleveland was the choice of Ford NASCAR teams and by the mid '80s would turn in dominating performances. As well, Clevelands were a mainstay in NHRA Pro Stock for years, with the likes of Wayne Gapp and Bob Glidden winning multiple national championships. And perhaps to end any debate, Hot Rod recently faced off a Boss 351 against several other notables including the LT1 350, L76 327, DZ 302, and Boss 302. The end result? The Boss 351 was proclaimed "the baddest small-block of the muscle car era."