With a good turbocharger, you should be making 350 to 400 hp at the wheels at this point, maybe even 450 hp if you have the timing and tune really dialed in. If you decide you still want to step up to the 14mm/4mm combo, then we would suggest an Aeromotive A1000 fuel pump, an AirDog 250, or a FASS 200. Get a fuel pressure gauge and a bypass-style pressure regulator, make sure it never dips below 15 psi, and know that you're on the ragged edge as far as injection pump reliability goes with this combination.
Q: I had some questions about how you would build a drag truck ("The Perfect Diesel"), as seen in the March '09 issue. Why ditch the turbo for a supercharger-especially since you said it would take 200 hp to turn?
Harry Wagner
Albuquerque, New Mexico
Although superchargers are...
Although superchargers are common on high-horsepower gasoline and alcohol applications, they've yet to make the jump to the competitive diesel market.
A: We've gotten quite a bit of interest from people wondering about diesel supercharging since we ran that article on how we would build our dream trucks. In our theoretical drag truck buildup, we mentioned we'd use a PSI screw supercharger atop a 6.6L Duramax. While it may sound odd to those familiar with turbochargers, there are several advantages to supercharging.
First and foremost, throttle response would be instant. Since the supercharger would probably be making 5 psi of boost at idle, there would be no time spent spooling turbos. This is particularly favorable in sports like drag racing, where competitors are trying to spool very large turbochargers within a few seconds. With a supercharger, there would be no waiting, just hit the throttle and go!
Another common belief is that superchargers can't move enough air to work well in a diesel application. In Top Alcohol Funny Car racing, enormous screw superchargers are used to generate up to 40 psi of boost on a 500ci (8.0L) engine operating at 8,000 rpm. On a smaller engine that is turning slower (such as a Power Stroke, Cummins, or Duramax) the same blower speed could create even more pressure-something like 70 to 80 psi, which is more than enough to support a high-horsepower diesel engine.
One of the biggest advantages of turbocharging is that it is considered to be free horsepower. Expanding exhaust gases and heat can be used to drive the turbocharger, taking almost no power away from the engine. In fact, using exhaust pressure to spin a turbocharger costs about 1-percent rated power per 10 psi of drive pressure. So in a stock 300hp diesel producing 20 psi of boost pressure (intake side) and 30 psi of drive pressure (exhaust side) the turbo would only be using up 9 hp-pretty close to free power
In diesel racing applications however, turbochargers start to become less efficient. A single turbo on a 1,000hp diesel racing engine may produce 80 psi of drive pressure or more, which means the turbocharger would be taking almost 80 hp to turn. At these power levels, taking 200 hp to drive a supercharger doesn't sound so bad. In our minds, we'd be more than willing to trade 120 hp for instant boost. A supercharger is also less sensitive to camshaft design and head work (which are needed to help large turbos spool) and boost is available over a much broader rpm range, which means more low end torque in high-rpm applications-the best of both worlds.