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Actually, core shift is malfunction in the casting process of the block. The block ends up with thinner walls on one side of a cylinder as apposed to the the other side. Then, if the block is later bored, one side of the cylinder wall can be too thin. This is especially important with thin wall casting techniques as used with the 289 and Ford small blocks in general. Unequal cylinder wall thicknesses lead to uneven heat expansion and non round cylinder bores which means loss of efficiency and power, lots of blow by and short engine life..

Sonic testing can detect this difference in cylinder wall thickness before expensive machining and block preparation is done. Sonic testing is a part of "blue printing" an engine. That will determine if the cylinder walls are of equal thickness around the circumfrence and if in fact there was a "core shift" problem in the original manufacture of a specific block. Early detection of core shift can save lots of grief and expense later on, (IE, after the engine is built and installed).

Because of the thin wall casting technique, .030" over bore is usually the max. for these engines.

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