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Old February 22nd, 2005, 14:10   #55
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Join Date: May 2000
Location: High Peak, UK
Fuel Economy: 35 if I'm lucky.
Default Re: Breaking News: New VAG 504.00 & 507.00 standa

Dan, IIRC OHC engines have fewer components than pushrod engines, which is why they have been adopted on common or garden passenger car engines. Its unlikely that an engine manufacturer would be fool enough to build a more expensive engine for diesel use, with less commonality. Re the multi-valve philosophy you approve of, I suspect its just aping the latest trends without understanding that the reasons for them are to do with the induction system limitations of naturally aspirated, high revving petrol engines. In the latest VW turbo diesels the 4-valve head is primarily to permit optimal injector positioning. With forced induction, and the oxygen rich combustion process of an unthrottled diesel, there is no need for variable valve timing to improve flow rates. Given an excess of oxygen, which is assured in the diesel engine, power requirements are modulated through the fuel injection system. If, for example, you were to fit a higher lift camshaft, there would be no power increase, because there is no benefit to be gained through better flow. There is more than enough oxygen available already as the engine runs "weak".
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