Hi,
First off variable valve timing does not occur by changing tension on the timing chain.
The variable cam gear design allows controlled play (kind of a slip fit) in the cam gear, as there is the driven portion (chain side) and a driving portion connected to the cam. The cam gear has chambers inside that fill with oil. Oil pressure is bled into chambers of the cam by an actuator that opens an oil pressure port to the cam gear. This adjusts the advance or retard of the cam. As the oil fills the chambers, it alters the original orientation between the gear and the cam, causing the cam to either move ahead (advance) or move back (retard) in relation to the driven (chain
part) gear. Some designs only control one cam (intake or exhaust) and others control timing on both camshafts. I have not seen details of the Ford system so can not say if one or both cams are controlled in each cylinder head.
As for an upgrade to an '02 engine, no way. Because the system is controlled by oil pressure, you would need cylinder heads, camshafts, cam gears, the actuator and the power train control module (computer). If you want/need 28hp that bad, it would be cheaper to trade up. If money is no object, wait until a totaled '03 is available and swap drivetrains. Another idea, when the new supercharged Lincoln LS debuts in 03, get one of those engines.
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2002 TBird Premium, Full Blue int.
1971 442 Vista Cruiser
1967 Ford Country Squire
1962 Oldsmobile Starfire Convertible
1932 Ford Roadster (on drawing board)