Ford Y-Block
Due to Ford's propensity for juggling its engine lineup by constantly introducing new platforms, even Blue Oval buffs have a hard time keeping all of them straight. While most hot rodders are familiar with Windsors, FEs, Clevelands, and 385-series big-blocks, few people realize the significance of the Y-block platform. Introduced in 1954, the Y-block is essentially the nexus between the legendary Ford flathead and every production V-8 built after it that used an OHV valvetrain. Although pushrod valve actuation is often ostracized by the general public these days, back in 1954 it was ground-breaking technology. The Y-block beat the small-block Chevy to market by a year, and as such, it was one of the first mass-produced passenger car V-8s to incorporate an OHV valvetrain architecture. The engine's deep-skirt design resembled a "Y," creating a very robust bottom end and earning it the Y-block moniker.

The Y-block was offered in 239, 256, 272, 292, and 312ci configurations. The original 239 was rated at 130 hp, a big jump over the 106hp flathead it replaced. To keep pace with the 265ci small-block Chevy that was unveiled in '55, Ford countered by boring and stroking the Y-block to 292 ci. The hottest version of the platform was the 312, introduced in '56. It boasted a four-barrel carb and 9.0:1 compression, producing a stout 235 hp. Many dealers offered the M260 engine kit as an option, which included a set of high-flow heads, a bigger cam, and dual four-barrel carbs that bumped output to 260 hp. The 312 was certainly a strong performer, but when the small-block Chevy was enlarged to 283 ci with a matching 283 hp in fuel-injected trim, Ford had to fend off the attack to remain competitive in NASCAR competition. It responded by strapping a McCulloch/Paxton supercharger to the 312, bumping performance to a cool 300 hp. This engine was so dominant that not only did it win 26 races to Chevy's 21 in the '57 NASCAR season, it also prompted the sanctioning body to ban it altogether. To ensure that enough supercharged 312s were built to meet homologation requirements, Ford installed it throughout its model lineup. This led to some interesting applications of this blown mill. It's not surprising that the supercharged 312 showed up in Thunderbirds, but it was also dropped into cars like the Fairlane, Skyliner, and Country sedan.

Despite its success, the Y-block V-8 was phased out by the mid '60s in favor of the FE in large car applications, and the Windsor in the small-car market. Downsides to the Y-block platform included poor top end oiling, and an odd cylinder head configuration in which pairs of intake ports were stacked on top of each other, impairing high-rpm airflow. Furthermore, the Y-block was small both externally and internally, and Ford was hesitant to push displacement beyond 312 ci. Even so, the Y-block V-8 often outperformed its small-block Chevy competition, and it has seen a resurgence in popularity as of late, thanks to the rat-rodding movement.

"...the Y-block V-8 often outperformed its small-block Chevy competition, and it has seen a resurgence in popularity as of late, thanks to the rat-rodding movement."

Chevy LT5
With the introduction of the C4 Corvette in '84, enthusiasts raved about the world-class handling provided by its solid chassis and all-aluminum suspension. Unfortunately, hitting the gas pedal served as a painful reminder that horsepower was just starting to recover from the doldrums of the smog era. Corvette Chief Engineer Dave McLellan's solution was building a 400hp version of Chevrolet's flagship with aspirations of making it the fastest production car in the world. Considering that the Corvette's L83 small-block produced a wheezy 205 hp, this was quite an ambitious plan to say the least. Chevy toyed with turbocharged six- and eight-cylinder prototype engines before settling in a naturally aspirated V-8. Right around the time the LT5 program was taking shape, GM acquired Lotus. Consequently, Chevy and Lotus engineers determined that the 400hp target could best be achieved with a DOHC, 32-valve V-8, and the LT5 engine program was born.

GM originally contemplated fitting DOHC cylinder heads onto the existing 350 small-block Chevy, but Lotus engineers insisted that a clean-sheet engine design would be ideal. The result was an engine based on an all-new aluminum block that shared little more than its 4.400-inch bore spacing with the small-block Chevy. The minimum thickness requirement of the cylinder liners resulted in a slightly reduced bore size of 3.900 inches compared to the Gen I small-block, which was combined with a 3.660-inch stroke. Speaking of liners, the LT5 block used aluminum sleeves instead of iron. To make this possible, the liners were coated with Nikasil to reduce friction, a common design feature of BMW and Ferrari engines of the era. The crank and rods were both forged, while the hypereutectic pistons squished out an 11.25:1 compression ratio. The short-block was fortified with iron main caps that used an integrated girdle assembly. Like the LS1 that would someday replace it, the LT5's oil pump was driven off the front of the crank.

Without question, the LT5's most impressive pieces of hardware were its multivalve cylinder heads. In addition to their four-valve-per-cylinder design, these heads were matched with a variable-stage intake manifold featuring two intake runners per intake port. The end product is three throttle bores, 16 intake runners, and 16 fuel injectors. At low rpm, a small 22mm bore throttle plate feeds air into the intake, then two additional 59mm bores open as engine speeds increase to maximize both airflow and charge velocity. Since the LT5 was designed before electronics were advanced enough to operate variable valve timing systems, it employed several design elements that net a similar effect. The two intake ports used for each cylinder were staggered in size, with the secondary ports measuring slightly larger than the primary ports. The lobe profiles on the intake camshafts were staggered as well, with more duration for the secondary valves and ports. As a result, the LT5 shut down the secondary ports using an auxiliary throttle plate integrated into the heads at low rpm to preserve port velocity and bottom-end torque, then opened them up top for high-rpm breathing. After final R&D was completed, GM enlisted Mercury Marine to manufacture the production LT5.

When the LT5 debuted in the '90 Corvette ZR1, it produced 375 hp and 370 lb-ft of torque. For the '93 model year, output increased to 405 hp and 385 lb-ft, thanks to cam timing changes and improved cylinder heads. As impressive as its technical specs were, enthusiasts complained that the LT5 was soft on torque at low rpm. This could easily be cured with today's variable valve timing technology, but the LT5's biggest problem was the LS1. Recognizing that they could achieve power figures similar to the LT5 in a smaller, lighter, and far less expensive engine package in the LS1, GM engineers bid farewell to the 32-valve wonder after the '95 model year. Despite its ignominious fate, the LT5 was one heck of a performer for its day.

"...the LT5's biggest problem was the LS1 ... GM engineers bid farewell to the 32-valve wonder after the '95 model year."