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copbait73 copbait73 is offline
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Join Date: Nov 2003
Location: Chesterfield IN
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As with many things you need to establish goals. Most of the guys on this board want fire breathing turbo motors for their 930 cars, however with restraint there are custom built turbo motor options for installation in lesser Porsche 911 based cars. Choosing this route you can also build a much lighter overall drivetrain.

As mentioned earlier the magnesium case has its limitations. Some speak to HP and others heat but they are one in the same. To produce a fixed level of HP you will produce and need to reject a fixed level of heat. Heat is the enemy of all motors but an especially troublesome and limiting factor for air-cooled motors.

If you do not track your car you should be capable of producing 250-275HP turbocharged and retain the weight savings of the magnesium case. A 2.4L based motor with 7R crankcase, E cams, T pistons (7.5:1) with existing modified CIS should do it. Turbos are generally light, wastegates not so, but this can be done with a much lighter package of small K16 with integral wastegate. l would avoid the temptation to bore this crankcase for larger cylinders, stay at 2.4L.

If you are driven to extreme weight reduction you could use the non-counterweighted 66MM T model crankshaft and a 2.2L motor, however you would need to drop compression to 7:1 and bump the boost to high level make up for the reduced displacement and RPM limitation this crank represents.

The added benefit of this small motor/ limited HP approach is you control torque and retain the lighter 915 magnesium case. Just build it with short or long gearing. All this assumes you also desire an austere car weighing <2200#.

Other considerations-
Valve covers: AL are more robust and will remain flat longer. If those two considerations are subordinate to reducing weight, mill your four magnesium covers flat and use them. When or if they distort and leak do it again.
Timing chain housing/covers, use them.

Last edited by copbait73; 02-10-2010 at 08:39 AM..
Old 02-10-2010, 08:13 AM
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