Turbocharging results in new top end for Perkins 700 Series

Diesel Progress North American Edition, July, 1999 by Mike Brezonick

When an industrial engine manufacturer develops an engine, it very typically targets it toward a specific horsepower and application range. But very often, with an eye toward the future, the manufacturer will build in some room to grow.

So it has been with Perkins, which recently unveiled a new top end to its 700 series of liquid-cooled engines that debuted in 1996. The new 704-30T diesel, which was introduced at ConExpo, is a four-cylinder, 2.95 L (from a nearly square 97 x 100 mm bore x stroke) engine rated 80.5 hp at 2600 rpm. With two torque ratings available - 187 ft.lb, at 1600 rpm and 169 ft.lb, at 1000 rpm - it is targeted at a range of compact equipment such as compact loaders, material handlers, forklift trucks, skid-steer loaders, directional drills, tractors, compressors and other industrial applications.

"Equipment manufacturers will benefit from the new 704-30T's compact profile that suits today's trend toward building smaller machines," said Mike Reinhart, director of marketing for Perkins Engines Inc., the North American sales organization of U.K.-based Perkins. 'It's a compact engine with exceptional power takeoff and excellent fuel economy.'

"One of the prime features of the 700 series is its compactness and in doing a turbocharged engine, we wanted to retain that," added Nigel Bacon, product manager, 700 series at Perkins in Peterborough, England. "Manufacturers have established frame sizes around engines and if we can offer more power in essentially the same package size, that gives our customers the opportunity for a range of models or a premium model.

Perkins 700 Series

Model           Displacement           Hp @ Rpm

704-26             2.60 L             57.7 @ 2600
704-30             2.95 L             52.0 @ 2600
704-30             2.95 L             63.0 @ 2600
704-30T            2.95 L             80.5 @ 2600

"There is no change to the length of the engine and the difference between the naturally aspirated 704-30 and the turbocharged version is a 2 in. difference in height. So that makes it easy for our customers to drop this into existing 700 installations without a lot of effort. We can also provide the same dress items - mounting points, engine flywheel arrangements, throttle actuation arrangements, filter positions, etc."

There is also approximately 80 percent parts commonality between the turbocharged and naturally aspirated engines, which Bacon said, "gives us advantages in production and also our customers advantages in service."

The key change is the addition of a low inertia Schwitzer turbocharger designed to provide fast response. Other changes include:

* A forged micro alloy steel crankshaft that is dimensionally identical to the existing version, but features heat treating improvements in the fillet region.

* Upgraded bearing materials.

* A reinforced top ring carrier on the three-ring piston ring pack to accommodate higher gas loads.

* Upgraded inlet valve material designed for high wearability.

* An integrated oil cooler with oil jets for piston cooling.

"Even with the additional weight of the turbocharger, the 704-30T is just over 500 lb.," said Reinhart. "That's remarkable in light of the horsepower it generates."

The basic geometry of the fuel system remains the same, with some notable changes to the injector nozzles and the Zexel fuel pump. The two-stage Bosch injector nozzles incorporate a new hole design to enhance fuel atomization - injection pressure is approximately 7250 psi, while the fuel pump incorporates a compact timing device (CTDs) that Bacon said "allows us to tune the injection timing far more closely over the speed/load range and gives us advantages on emissions control and also noise."

Combustion takes place by injecting fuel slowly at first, then, when burning has begun, injecting more rapidly into the re-entrant combustion chamber. This lowers the rate of pressure rise within the cylinder, and thus noise.

"Noise is a concern," Bacon said. "While we're always concerned about the top end figure, we're equally concerned about what the engine sounds like in normal operation. The CTD gives us an advantage in softening the engine note.

"You've always got some noise, it might as well sound good."

The engine also incorporates a closed circuit breather system, which Bacon said was rare for turbocharged engines in this range. "With closed circuit breathers, you can run into problems in a number of areas," he noted. "One of them is gradeability of the engine. A closed circuit breather can impose limitations on operating angles because suddenly you can find a slug of oil coming up through the system and being digested through.

"But with this system, we can operate at 30 [degrees] in all directions, which is good.

Like all of the 700 series models, the 704-30T diesel offers single side servicing and is covered by a comprehensive three-year warranty, Perkins said.

"There are over 37,000 700 series engines operating around the world," noted Reinhart. "It's been very successful and we anticipate that success to continue with this engine as well."