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Old 08-24-2012, 12:48 PM
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Originally Posted by Caprice Sleeper View Post
I have not been able to find any solid info on this subject. Is a 1990 305 TBI car engine with a factory roller cam a reverse coolant flow engine? The water pump is a reverse rotation design but does that mean the heads get coolant flow first? I want to make sure if I bolt on my 906 vortecs it won't overheat. I would think if my serpentine belt water pump is not compatible with the vortecs then I can just install the correct water pump and belt setup. Any clarity on the subject would be a great help. I will be running an edelbrock 2116 intake and a carb.

Thanks everyone,
No, the 305 is not a reverse coolant flow engine. Those are the 1992 thru 1997 LT1, the LT4 of 1996 and 97, and the L99, 260 inch engine of 1994 thru 1996. These are referred to as Gen II small blocks. These engines do not share basic castings of heads, block, or intake with the Gen I engines. However the crank assembly, cam, lifters, push rods, rockers, springs, valves, exhaust manifolds/headers will interchange with Gen I. The cooling system is way different using a pump driven off the camshaft with an integral mixing chamber that combines cold coolant from the radiator with some hot coolant from the engine to maintain the internal engine temp in a very tight heat range, The coolant flow is reversed from the Gen I where the Gen II reroutes coolant entering the block such that it is directed into the heads first. From the heads the coolant flows back into the block and returns to the mixing valve housing from passages in the block located under the inlet passages from the pump. Some history; Pontiac tried this type cooling on their V8ís from 1955 through 1959, it had problems with trapping gasses and steam inside the cooling passages of the head so was discontinued for a conventional system. It turned out the solution to making this work was a vent tube from the rear of the head back to vent the trapped gasses, which is seen on the LT1/4 and L99.

Gen I blocks all cool in the "normal" way of the pump introducing coolant into the front of the casting where it floods around the cylinder walls, then flows through passages into the heads. From the front of the heads it is gathered into a passage on the front of the intake manifold and returned to the radiator from the thermostat housing via a hose. This covers SBCs from 1955 to 1995 and G30 vans to 96. For the years 1955 through 1986 the SBC drove accessories including the water pump with V-belts, these rotate the water pump in the same clockwise direction as the crankshaft turns when viewed from the engine front. This is considered conventional pump rotation. In 1987 the SBC went to supporting the accessories on castings that bolt to the front of the engine in place of the sheet metal brackets previously used and with this change the multiple V-belt drive system was replaced with a single serpentine belt. The serpentine belt runs under the water pump pulley instead of over it as with the V-belt, this rotates the water pump in the opposite counter-clockwise direction to the V-belted engines. This also effects the fan blade pitch direction where the pump driven fan is used. These are considered to be reverse direction pumps not to be confused with the LT1, 4, and L99 reversed coolant flow.

One has to step around the pump rotation direction carefully when it comes to aftermarket serpentine belt systems some designs drive the pump with the belt passing over instead of under the pump pulley. These over the pulley type serpentine set-ups need to use the conventional drive direction (clockwise) pump.

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