S14 and S15 engines fitted with Variable Cam Timing (VCT) have one very small external difference in the front timing case. When viewed from the front of the motor the top left mounting screw on the front timing cover is moved about 15mm to the left on engines fitted with VCT. Whilst this may seem like a very insignificant diference the reason is very important.
On VCT engines an extra oil way has been added to the engine block and the front timing cover bolt had to be moved to accomodate this change. The extra oil way feeds the timing chain tensioner
This extra oil way runs behind the water pump and down to the main oil gallery. Its so close to the front of the engine that the water pump recess in the block has been made smaller on VCT engines resulting in a different water pump as well.
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Non VCT Engine "D" |
Engine fitted with VCT "B" |
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Front Timing Case Note the relocated mounting hole |
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Engine Block (looking at front right corner) Non VCT engine is missing the extra oil feed |
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Cylinder Head Extra oil hole that feeds the chain tensioner |
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Water Pump Recess On the VCT engine the water pump recess is not as deep to allow for the extra oil feed to pass behind the water pump |
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Obvoisly there is also a very subtle difference in the head gaskets to accomodate the extra oil feed as can be seen by this document produced by Permaseal.