The difference between 500 and 750 is only a matter of air and fuel. Pretty easy right? Well, we wish it was. The fuel part of the equation is quite challenging unless you have someone like PDR around who can build a custom injection pump. The 180 horsepower and 215 horsepower p-pumps are the best injection pumps to work with here. The pump will need to be torn down and "tweaked", higher timing set and the pump will need to be balanced on a bench test stand by someone who knows what they are doing. A custom camplate is recommended and EDM'd or extrude honed delivery valve holders are required to maintain 750 horsepower reliable. At this horsepower level, oversized injection lines should, also, be used to help flow the increased fuel to the injectors.
While 370 cc injectors have been able to make this horsepower, a custom set of injectors is the best option. These will be built to flow the exact amount of fuel for your desired horsepower level and engine modifications. Matching components at this level will make the difference between reliable, efficient horsepower and smoky, unreliable horsepower. Now that the fuel injectors have been upgraded and the injection pump flow more, the stock mechanical lift pump will need some help. An external electric lift pump that can flow a constant 25 psi of fuel pressure to the injection pump at all times is the best option for reliability.
The internal modifications that were made for 500 horsepower will work for this level as well with the addition of a block girdle and fire rings. The turbochargers will need to be larger. A good set of twins will flow the air needed while keeping the vehicle streetable will use a compressor wheel of 62mm for the high pressure and somewhere around a 72 to 76 mm compressor for the low pressure. While the compressor wheels are around the same size as the 500 horsepower, the turbine housings and turbine wheels will be different.
At this power level, "A good High Pressure water injection system should be used," says Joe Hellmann of Hellmann Performance. "By high pressure, I'm talking about 500 psi and higher," Hellmann continues. High pressure water injections systems allow for small incremental adjustments to fine tune the power level and EGTs.