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jluetjen jluetjen is offline
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Join Date: Oct 2001
Location: Westford, MA USA
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Interesting engine. Basically the performance of the 2.5ST motors falls pretty much on a straight line between the earlier 906 engine, and the later RSR motors (and BTW the 908 and 917 motors which in many respects are nothing more then 8 and 12 cylinder versions of a 911 motor). In the past I've posted data on the ST motors, both the long-stroke and the short-stroke versions. Generally the performance per liter of those engines is pretty much all on the same level. You listed the factors that provide that extra HP (not to mention the changes made to the engine to ensure long life at 8000+ RPM). For comparision, the 2 liter Cosworth BDG engine (think of it as half of a DFV that has been bored and stroked) made 280 HP way up at 9250 RPM, and 175 lb-ft of torque at 7000 RPM compared to the ST's 270 HP at 8000 RPM and 192 lb-ft at 5300 RPM.

Porsche discovered when they developed the 4-valve heads for the 956/962 that the 4 valves don't leave enough room to flow the air required and provide the surface area to cool the heads. So they developed water-cooled heads for the 956/962's in the 4-valve configurations.
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'69 911E

"It's a poor craftsman who blames their tools" -- Unknown
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Last edited by jluetjen; 03-04-2006 at 04:16 PM..
Old 03-04-2006, 03:02 PM
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