’s Boss 302 is remarkable because it achieves its prodigious output without forced induction and is a surprisingly pleasant daily driver.
The Ward’s 10 Best Engines competition has recognized outstanding powertrain achievement for 18 years. In this installment of the 2012 behind the 10 Best Engines series, WardsAuto looks at the evolution of’s 5.0L V-8.
Boot up your time machine. Forty-three years after its 1969 debut, and 41 following its untimely demise in favor of the ’71 Boss 351,'s Boss 302 is back.
Designed primarily to win Sports Car Club of America Trans Am pro-series races, the original 5.0L Boss 302 V-8 was driven by racing legends Peter Revson, Parnelli Jones, George Follmer and Sam Posey to four Trans Am victories in 1969.
It won six of 11 events and the series championship in 1970 against factory efforts from Chevrolet, Pontiac, Plymouth, Dodge and AMC.
Offered in striped, spoilered and suspension-beefed Boss 302 road-going Mustangs, that free-breathing, high-revving V-8 was rated at 290 hp at 5,800 rpm and 290 lb.-ft. (393 Nm) of torque at 4,300 rpm.
Its new Wards 10 Best Engines namesake pumps out 444 horses at 7,400 rpm and 380 lb.-ft. (515 Nm) at 4,500 rpm. That’s 10 less lb.-ft. (13.6 Nm) but 32 more ponies compared with the 2011 Ward's 10 Best Engines Mustang GT V-8 from which it is derived.
Because fuel efficiency plays a major role in the Ward’s 10 Best Engines competitions, most recent winners have been state-of-the-art I-4s or V-6s, plus a handful of hybrid and battery-electric powertrains.
"If the industry is moving in this direction," says editor Tom Murphy, "so should the list. But we will never forsake the engines that ooze testosterone and conjure images of smoking tires and parachutes pulled taught from a reinforced rear bumper."
So WardsAuto judges put this very special new V-8 on the 2012 list.
What makes it notable is the seriousness of the team that developed it and the long list of performance and durability-enhancing upgrades they added. The new Boss 302 also is remarkable because it achieves its prodigious output without forced induction and is a surprisingly pleasant daily driver.
We asked Kevin Tallio and Jagadish Sorab, technical leaders for the top and bottom ends, respectively, of the 5.0L V-8, about the design priorities for altering the 2011 base engine.
"We knew we were reproducing an icon, so we wanted world-class horsepower and torque,” Tallio says. “Dual overhead cams with cam phasing allowed us to tailor the torque curve for a lot more mid-range, while being smarter about the combustion process enabled a higher compression ratio."
The goal was a much more powerful, but also more fuel-efficient, dual-duty all-aluminum V-8 for performance cars as well as workhorse trucks.
While peak power surged to beyond 400 hp from the outgoing "modular" V-8 GT's 315 hp, some 60 grams (2 oz.) of mass per cylinder came out of the pistons and connecting rods.
"We did that for friction reduction, but it also lets us rev to much higher speeds, which is relevant to the Boss 302," Sorab says. “And piston ring tensions are 20% lower to reduce friction.
"The capability to spin this engine to higher speeds was key," Tallio adds. "We completely redid the cylinder head and went to a compact RFF (roller-finger-follower) valvetrain for a significant weight reduction."
Engineers also provided package space in the heads to enable higher lift for the Boss 302 version of the original engine, up to 13 mm (0.5 ins.) for both intake and exhaust valves vs. 12 mm (0.47 in) in the base V-8.
“We also did a lot of work optimizing airflow because airflow is the key factor in torque,” Tallio says. “We're pushing close to 100% volumetric efficiency at peak power, which is quite an accomplishment given all the constraints we have in a production vehicle installation."
Among the Boss 302's upgrades are a new-design composite intake manifold inspired by Ford's Daytona prototype racing engines. It features shorter runners for high-rpm breathing; high-strength aluminum heads with CNC-machined ports and chambers (for exceptional high-rpm airflow); forged aluminum pistons and sinter-forged connecting rods; racing-spec rod and main bearings; and hollow intake valves, sodium-filled exhaust valves and other lightened valvetrain components for high-rpm, high-temperature operation.
"Our original horsepower target was 430, and our goal on torque was to not lose much from the base engine. To make those numbers, we had to push engine speeds up to take complete advantage of this engine's 7,500-rpm design capability," Tallio says.
The new intake manifold's runners were shortened by about 2 ins. (50.8mm) to push the engine's power peak up to 7,400 rpm. Much time and effort was spent using computational fluid dynamics analytical tools to understand and better define port flow, and the team decided to CNC machine the ports and chambers to ensure control of port geometries. That painstaking process requires 2.5 hours per head, Ford says.
After increasing valve lift to 13 mm to take full advantage of the engine's maximum lift capability, cylinder pressures were boosted for additional torque. That required an upgrade in cylinder head material to an AS7GU aluminum alloy for more strength and high-pressure capability.
Interestingly, the base engine's piston cooling jets were not used in the Boss 302. "We needed to go to much higher speeds, and all that oil dripping in the underside of the engine would cause aeration and windage loss," Sorab says. "Eliminating those bought us a few more horsepower, and we compensated by upgrading the material of the pistons and connecting rods. We also went to tri-metal bearings to handle the higher speeds."
For improved oil control under high cornering loads, the Boss 302 uses 5W50 synthetic oil instead of the base engine's 5W20, an engine oil cooler and revised oil-pan baffling.
"The new windage tray is one of the most effective we have ever designed and the thicker oil reduces windage and gets us much better pressures at high speeds,” Sorab says.
"We have an internal limit of 10% aeration at maximum speed, and this engine comes in at 8%, quite an accomplishment. We never have measured aeration this low."
An early durability run of Boss 302 prototype engines in Boss 302R race cars came in the January, 2010, Daytona 24-Hour endurance event. The team collected race telemetry data to help optimize engine calibrations and oil pan designs and cooling, and then used that data to recreate Daytona race lap conditions on a test dynamometer.
While fuel economy hardly is the mission of this wonderfully muscular V-8, it offers a very respectable 17/ 26 mpg (13.8-9 L/100 km) city/highway with the standard 6-speed manual gearbox, and Sorab says there still is plenty of room for improvement.
"This engine has not seen the end of its run by a long shot," Sorab says. "I think there are improvements available in both friction and airflow."
Not to mention the potential addition of direct fuel injection.
"We do have some things up our sleeves," Tallio adds with a wink and a grin.