Sumps vs. Pick-up Tubes and EFI
EFI and modern engine technology have combined to create the ultimate street-driven racecar. With ordinary combinations producing between 300 HP and 500 HP, the stock EFI fuel system has proven flexible. Hard core engine combinations exceed this mark with the exotic, making 1000+ HP on the street. Applications above 500 HP universally require a complete fuel system makeover, from fuel rails to fuel pump. A key part of any fuel system upgrade is the tank itself. The debate is whether to modify the stock tank or install a racing fuel cell.
There are several benefits for retaining the stock fuel tank in a high horsepower street car. It has a larger capacity than most fuel cells, already has a mounting location and hardware, has provisions for filling from outside the vehicle, has a cap that both vents and seals, and is already on or in the vehicle.
The drawbacks to stock fuel tank retention are more numerous but less obvious. The stock pick-up/pump assembly is restrictive, which requires a complete replacement with a fabricated assembly. When using a stock tank with fabricated pickup, the internal well (which the stock pump draws from) is far too small and poorly supplied with fuel from the rest of the tank. That is, unless the fuel level in the tank is ¾ full or higher. Faced with the demand of a large pump drawing through a fabricated pickup, it has no chance of refilling fast enough to support wide-open throttle full engine load. Under low demand and cruise-type conditions, the large volume of fuel delivered to the rails is unused and returned. The same fuel, picking up heat from the pump and the rails, is constantly recycled to and from this well, rapidly increasing fuel temperature. Common problems associated with stock fuel tanks and fabricated pickups are pump cavitation, vapor lock, varying fuel pressure, exaggerated pump wear, and lean conditions during both low and high loads. Note: unlike a carbureted engine, any loss of fuel supply at the in-tank pickup will immediately result in a loss of fuel volume and pressure at the EFI injector, resulting in lean conditions and engine damage.
For those who prefer a stock-style fuel tank, Aeromotive has performed extensive research into what would make an acceptable compromise. The findings above clearly ruled out the use of any kind of fabricated pickup. Instead,we designed a fuel sump and baffle assembly that is professionally installed on various stock-style tanks. The primary problem of heat soak is minimized, as is the restriction of fuel flow through the sump box and to the actual pick-up point. However, this is still a compromise, at best, requiring fuel levels be maintained above ¼ for normal low load driving, above ½ to ¾ for drag racing, and above ¾ for road racing. In all serious racing applications, the correct fuel cell is highly recommended. All Aeromotive fuel systems are available with or without the modified stock tank, allowing the best choice of fuel container without compromising the rest of the system. There is a better way to feed the beast and Aeromotive has the modern fuel system components to do it now!