Form follows function is a credo that was originally applied to modern architecture by Horatio Greenough. The phrase applies to modern diesel trucks, too, particularly David Busch's '04 Dodge Ram 2500. Instead of focusing on shiny rims and a fancy paintjob, David put every dime of his money into making his truck as powerful as possible. To highlight the point, consider that when David received an insurance check for hail damage to the hood, fenders, and roof-he spent the money on his Cummins' cylinder head instead!
650 HP On Fuel
David ported the exhaust-side of the cylinder head himself and had Pro Machine in Rapid City, South Dakota, give it a five-angle valve job before adding Hamilton valve springs and chromoly pushrods. A high-pressure S364 turbo sits on top of a low-pressure S400 combined with plumbing from Wicked Diesels to create approximately 60 psi of boost. ARP head studs keep the head gasket from parting ways under the incredibly high cylinder pressures, while drive pressure is controlled by a Tial 46mm external wastegate. A huge AFE dry-flow filter handles the air intake, and a full 5-inch exhaust from the S400 feeds into a 6-inch stack in the bed. "The 5-inch downpipe was a chore to route," David admits, "but it provides hardly any backpressure and helps the EGT." Exhaust gas temperature is still a concern with the 120hp DDP injectors, even with all of the airflow. Fuel is fed to the injectors by a FASS 150-gph lift pump that pushes diesel to a CP3 injection pump modified with an Arson III kit from Wicked Diesels. The combination makes 651 hp and 1,249 lb-ft of torque-and that was before the headwork was performed.
 The huge AFE dry-flow air...  The huge AFE dry-flow air filter provides enough clean air to support the twin turbos, and it never needs to be oiled. The only downside is that space restrictions do not allow for a heat shield around the turbo. |  The truck uses an S364 turbo...  The truck uses an S364 turbo over an S400 with an 80mm compressor wheel. This allows near instantaneous spooling with power that is still pulling hard at the 4,300-rpm rev limiter. |  David modified the Bosch CP3...  David modified the Bosch CP3 injection pump with an Arson III kit from Wicked Diesels. The pump now flows plenty of fuel to keep up with the 120hp DDP injectors. |
 David ported the exhaust-side...  David ported the exhaust-side of the ISB Cummins head and fitted it with Hamilton chromoly pushrods and upgraded valve springs before screwing it back onto the block with ARP head studs. |  Instead of spending money...  Instead of spending money on an aftermarket intake manifold, David made his own from a flange and a single mandrel-bent tube. It may not be the prettiest, but it is both cost- and performance-effective. |  A Tial wastegate was used...  A Tial wastegate was used to adjust drive pressure for different driving conditions and environments. David typically runs around 60 psi of boost pressure, evenly divided between the two turbochargers. |