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Old 05-17-2012, 02:38 PM   #3
Steve Tinker
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Join Date: Dec 2008
Location: Queensland, Australia
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Soetekouw......

Most twin cam engines have an intermediate sprocket (chain drive) or roller (belt drive) to lower the camshaft rotational speed to the required half engine crankshaft speed.

The main reason the M96/97 engines have a hollow "shaft" running the length of the engine is because of Porsches (financial ?) decision to have both cylinder heads identical, requiring a drive from the front for one cylinder head and a drive from the rear for the second cylinder head. If Porsche had designed, built and accepted the extra cost of a second "mirror image" cylinder head then most of the IMS drama would possibly not have eventuated.

The other alternative is to reduce the camshaft speed down the 50% by altering the size of the camshaft sprocket, which the new DFI engines use I believe. But therein lies another potential wear problem in that the timing chains are now running at engine speed - up to 7,800 rpm on the new Boxster engines - so its a matter of time as to how the chains, sprockets and tensioners on the newer engines lasts.
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2001 Boxster S (triple black). Sleeping easier with LN Engineering/Flat 6 IMS upgrade, low temp thermostat & underspeed pulley.
2001 MV Agusta F4.

Last edited by Steve Tinker; 05-17-2012 at 02:42 PM.
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