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Old 01-15-2013, 01:48 PM
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Here is an outline of the procedure if you decide to drill the holes.....
Technical Articles at Greg's Engine & Machine
In my opinion, I wouldn't run a 400 without them. GM engineers found a need for them at low rpm's. Steam pockets would form at the blind corners of the water jackets as a result of the cylinders being siamesed. These pockets of steam would heat that little area and either cause pre-ignition or would cause the motor to spit out the head gasket. I am unsure as to whether or not the engineers tried running a hose from the back of the heads to the water pump, but if they did, it apparently didn't work as well as drilling the steam holes because I know of no factory bypasses, only steam holes. No steam holes are needed if the motor is to see duty in the higher rpm range, such as in a racing application. The speed of the water through the water jacket due to higher water pump impeller speeds will wash away any steam pockets that may try to form. It's only a problem at lower rpm's.

Last edited by techinspector1; 01-15-2013 at 01:57 PM.
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