Reaching 500 Horsepower
Since the diesel horsepower wars hadn't started yet, the early 12 valve engines needed quite a few modifications to start showing their potential. The 12 valve engines that came with the VE injection pumps (1989 to 1993) will require more money and effort to reach the 500 horsepower mark and beyond. Most agree that these engines should be updated with the Bosch P7100 p-pumps. It doesn't seem to really matter which pump you choose (the pumps were rated at different horsepower depending on the trucks OE horsepower rating) for the 500 horsepower goal.
Once the p-pump conversion has been completed, changing the camplate to a number 10 or a custom 100 is a good place to start. The number of the camplate represents the factory horsepower rating. The higher the camplate number, the lower the horsepower rating (with the exception being custom plates). Next, the delivery valves in the pump will need to upgraded. "I like my Taper Cuts for street use, as it fuels like a set of 191's but without all the bottom end smoke," Says Mark Wilson Sales and Technical Manager for PDR Diesel Performance. "For competition use, I recommend full cuts," Wilson continues "They will flow the most fuel but are not recommended for street use." Feeding the injectors more fuel only works if the injectors can flow more. So, upgrading to 370's will work if you don't mind being a little smoky. Otherwise, a custom set of injectors with honed or EDM (Electrical Discharge Machining) tips will do a much better job of delivering the horsepower while maintaining a relatively clean burn. Increasing the rpm's of the engine will, also, help free up some horsepower. A three or four thousand rpm governor spring kit will do just that.
For good useable power above 400 horsepower, our expert panel recommends using a set of twin turbochargers. The high pressure turbo (the small turbo) can be a HX35 (stock turbocharger on the second generation 12 valves) with a low pressure (the large turbo) using a compressor wheel around a 72 to 76 mm. This combination is very streetable, manageable EGT's, while still being able to tow and use the truck, well as a truck.
Once you have the air and fuel, it is time to address the engine itself. Head studs are strongly recommended at this power level and a good idea anytime you are going into the engine. There was some differences between fire ringing (o-ring) the head or not, but most say this is a good power level to think about adding it to. Adding a good efficient cam will yield better fuel efficiency and more power. When modifying the cam and turbo, it is always a good idea to upgrade your entire valve train to help everything running properly. "Anytime you are dealing with boost levels above 30 psi, the valve springs start loosing their effectiveness and the valve start to unseat," says Zack Hamilton from Hamilton Diesel Cams. "This can cause catastrophic problems and eventually cause engine failure," continues Hamilton. In addition to upgrading the cam, adding a cam retainer and crank gear retainers are, also, recommended at this power level. Anything above, they are needed as the increased stress from the higher performing injection pumps tends to walk the gears off.
The final part of the puzzle is the transmission. "At around 450 to 500 horsepower we recommend people to do at least a rebuilt unit with upgraded clutches," says Ron Wolverton from Sun Coast Transmissions. "Depending on how hard you drive will depend on what internal components need to be made out of billet," continues Wolverton. "Remember, none of these transmissions are new."