Inside Gale Banks Engineering’s New Blown 7.1L Duramax
Diesel Power
January 2012
Gale Banks has already set drag strip records with the twin-turbo version of this Duramax engine, and now they’re swapping out the turbos for a supercharger.
Deep within the prototype building of Gale Banks Engineering lies an assembly room where some of the most powerful twin-turbo Duramax engines ever built were born. While most of us are familiar with Banks’ diesel performance parts, very few people have seen inside the Banks research and development facility. It’s an R&D department that comes with an extra R — and that R stands for racing. In simple terms, no one else in the diesel industry has anything like it.
Yet on our recent trip to the Banks R&D&R department in Azusa, California, we weren’t there to see turbochargers – we were there to see a supercharged 7.1L Duramax. Behold, this 433ci Duramax, we’ve dubbed Megamax, features an ’11 LML engine block (the strongest D-Max block ever built), a billet-steel stroker crank, H-beam Carrillo connecting rods, and forged-aluminum Mahle pistons. Rounding out the long-block are a set of production LML-based cylinder heads that have been CNC-ported and blended to match a one-off aluminum intake manifold bolted between the heads. Fueling the Megamax is a pair of beltdriven CP3 injection pumps and two progressive stages of nitrous and water-methanol.
THE LOUDEST DURAMAX ON EARTH This engine is destined to speed the Banks dragster down the quarter-mile in 2012, and when it does, you’ll be able to hear its 2 ½-inch zoomie headers from a mile away. ‘Cause without any turbos to restrict the exhaust flow, this supercharged Duramax will be the loudest common-rail diesel you’ve ever heard! We can’t wait to see it run.
Within Banks’ engine assembly clean room, the 7.1L Duramax engine build began by hanging the Mahle forged-aluminum pistons on billet-steel Carrillo connecting rods. Each tool-steel floating pin was lubed and slid into its respective piston and rod.The Mahle pistons feature coated skirts and custom Total Seal rings. You’ll note that the top ring lands are hard anodized to keep the top ring from wearing into the piston.All ‘11 LML Duramax engines feature this heavily reinforced block. Note the extra ribbing in the casting (A) and the structural bulges (B) that strengthen the crankcase. To this foundation, Banks added a 4.150-inch-stroke, internally balanced, billet-steel crank from Sonny Bryant to push displacement to 7.1L. The crankshaft spins on Clevite H-series bearings and is secured with 14mm ARP main bearing cap studs.Each piston rod was lubed and slid into the block. From this angle you can see the wide, smooth piston bowls that have had valve reliefs cut into them for the 0.555-inch lift camshaft.The pistons were installed in the block to be within 0.012 inch of the top of the engine deck. ARP Custom Age +625 material head studs were fitted to the block, but you’ll notice that there are no grooves cut in the head for fire rings. This engine relies on an in-house-machined deck height, and stock, multi-layer steel head gaskets to seal in cylinder pressure.The heads are based on production’11 LML castings that were ported to flow 250 cfm. The valvetrain is where the engine starts to really deviate from stock. You’re gazing at Inconel intake and exhaust valves that are sprung with single-rate 260-pound springs with titanium keepers. Surprisingly, blueprinted production rocker arms, rocker shafts, and valvespring bridges were deemed adequate for this build. The camshaft was then degreed in 6 degrees after top dead center. Banks’ supercharged Duramax intake began life as a single chunk of 6061 aluminum. The large center piece was cut in-house on one of Banks’ CNC mills and features an open-plenum design – but no intercooler. Nitrous will be sprayed directly into the manifold from four nitrous ports to provide supplemental oxygen and cool the intake charge. Connecting the supercharger manifold to the heads are these CNC-machined, port-machined intake runners that are literally works of art. To produce the most possible airflow, all three pieces of the intake were assembled and hand-blended to remove any material that might restrict the air forced into the combustion chambers. Smooth intake ports are like a perfect fire escape; they direct the air precisely and quickly, without the air having to struggle to get where it’s going. Smooth-moving air stays cooler, moves faster, and fills each cylinder more completely so that each power stroke can product more power. With the intake installed, a 4.0L Lysholm-style supercharger was bolted on top of the lifter valley. This stealth-black blower is far removed from the 6-71 roots-type superchargers you’re used to seeing on diesels. It features screw-type rotors that compress air between – not below – each other for ultimate efficiency, less heat production, and more boost pressure potential. Feeding the fire are Bosch injectors that flow more fuel than stock. It’s also worth mentioning that the Megamax will not use a conventional geardriven water pump, rather it’ll be fitted with an electric pump that permits the team to circulate coolant through the engine between dragstrip blasts. To drive the supercharger, Banks fabricated its own harmonic balancer and blower drive system derived from its marine and military Duramax engine programs. The dry-sump oil system is made up of two pressure pumps and five scavenging pumps that literally vacuum the lubrication oil out of the engine. This system practically eliminates power loss from oil sloshing around in the engine and slowing moving parts. Drawing a vacuum in the crankcase also allows the engine to run reduced-friction piston rings – freeing up power and reducing engine wear.
