Remember, the crank pulley must match the accessory drive system you are using. All production A/C compressors are located low on the passenger side. In many applications it will hit the frame in this location. There are a number of aftermarket companies that make brackets to relocate the A/C compressor to a location above the thermostat housing. This can eliminate the requirement to modify the frame.
Cooling SystemsAll LS water pumps share a common bolt pattern, and will interchange between engines. This allows you to use an LS3 water pump in space-confined applications. It works with most accessory drive systems, and is much shorter (over one inch) on the front compared to a LS1 pump.
Both radiator hoses come out on the right side of the engine. This makes it difficult to install the upper radiator hose in some applications. Using a dual-pass cross-flow radiator allows both hoses to hook up on the passenger side. An additional benefit to dual-pass radiators is they keep the coolant in the radiator longer. This allows the fan to remove more heat, and it increases the ability of the radiator to cool more efficiently.
All LS based engines have a small hose connected to the front of the cylinder heads. In some applications, it is hooked to the lower left side of the throttle body, then to the radiator. Either way, this tube must be hooked to the radiator in the area of the upper radiator hose. It vents air from the top of the cylinder heads, and not hooking it up can cause engine damage.
Closed cooling systems, with a pressurized overflow bottle, cool better than a standard system with an open overflow bottle. The additional coolant in the bottle, plus the higher pressure, allows the system to cool more efficiently. This type of system is used in the Cadillac CTS-V, Pontiac Solstice, as well as other GM vehicles. They make good candidates to salvage used parts from. If you choose to install one of these systems, the lower line from the bottle should be tied into the return heater hose (the most forward 3/4-inch nipple on the water pump housing) on a LS engine. The vent hose from the cylinder head should be hooked to the small upper nipple on the bottle.
All production LS engines are built with a 195-degree thermostat. Never remove the thermostat from an LS based engine since it's designed to direct flow through the engine, and removing it can cause engine damage. You can run a lower temp thermostat, but remember the engine controller uses engine temperature to determine fuel and timing curves.
Fuel SystemsAll production LS engines are fuel injected. The engines are available with both "return" and "returnless" fuel rails. Early ('97, '98, and some '99) LS engines were equipped with return-style systems. These have two nipples on the fuel rail, the supply is 3/8-inch and the return is 5/16-inch. There's a regulator on the fuel rail that maintains fuel pressure. This regulator uses an internal spring and manifold vacuum to adjust fuel pressure based on engine load. Later LS engines ('99 and up) have a returnless-style fuel system.
These engines have one 3/8-inch supply line to the rail. A regulator must be installed before the fuel rail to maintain 56psi of pressure. The engine controller is responsible for all engine performance functions, with standard calibrations based on 56psi. Pressures above or below this number can cause engine performance issues.