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DC40 - MOD S Cams and 9.5:1 Pistons
Anyone tried this combination? I was going to run 8.5:1 RS P+Cs but am now going to go with the 9.5's. Are these cams compatible?
What setup should I be running on my webers? Calgary = 1049 meters (3300 feet) above sea level.
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06 Cayenne Turbo S and 11 Cayenne S 77 911S Wide Body GT2 WCMA race car 86 930 Slantnose - featured in Mar-Apr 2016 Classic Porsche Sold: 76 930, 90 C4 Targa, 87 944, 06 Cayenne Turbo, 73 911 ChumpCar endurance racer - featured in May-June & July-Aug 2016 Classic Porsche |
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my setup is webers, back dated exhaust, 35 intake port, 35 exhaust port, dc40 cams, and either 8.5:1 RS pistons or 9.5:1 JE's.
The engine is going together with one or the other tomorrow.
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06 Cayenne Turbo S and 11 Cayenne S 77 911S Wide Body GT2 WCMA race car 86 930 Slantnose - featured in Mar-Apr 2016 Classic Porsche Sold: 76 930, 90 C4 Targa, 87 944, 06 Cayenne Turbo, 73 911 ChumpCar endurance racer - featured in May-June & July-Aug 2016 Classic Porsche |
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Registered
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If you are ordering the JE pistons then just tell them what cam you are running and they will make the valve pockets accordingly.
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I already have both sets of pistons. The engine is going together today.
Nobody sees any issues with 9.5:1 pistons and Dc40's?
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06 Cayenne Turbo S and 11 Cayenne S 77 911S Wide Body GT2 WCMA race car 86 930 Slantnose - featured in Mar-Apr 2016 Classic Porsche Sold: 76 930, 90 C4 Targa, 87 944, 06 Cayenne Turbo, 73 911 ChumpCar endurance racer - featured in May-June & July-Aug 2016 Classic Porsche |
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Registered
Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
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First, the rule of thumb of not going past 9.5/1 CR is more for low overlap cams like SC/3.2 Carrera cams.
I am not an expert but my understanding from a conversation I had with someone at Web Cams years ago is that the CR of 2.4S & RS pistons is actually less than ideal for S or modified S cams. I suspect that 8.5/1 was in response to gas quality at the time and was a comprimize. I belive the RS CR can be bumped to about 9.3 during set up when setting the cylinder height. The factory new RS P&C is probably a better quality set up if new. The 9.5/1 is a closer to ideal CR I suspect and may still be a bit on the safe side for such a high overlap cam. Again, I am not an expert on this and would recomend calling the cam builder as they should better know the ideal CR to work with there cam. |
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I would rather be driving
Join Date: Apr 2000
Location: Austin, TX
Posts: 9,108
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You will be fine with the 9.5. In fact, it should run really well. Just make sure to verify the piston to valve clearance.
The DC40 has enough overlap that you should be fine on single plug. the overlap will lower the dynamic compression. Is this a 2.7? Just make sure to run the best gas you can get as you are on the edge of compression for single plug.
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Yes it is a 2.7. Thanks for the advice.
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06 Cayenne Turbo S and 11 Cayenne S 77 911S Wide Body GT2 WCMA race car 86 930 Slantnose - featured in Mar-Apr 2016 Classic Porsche Sold: 76 930, 90 C4 Targa, 87 944, 06 Cayenne Turbo, 73 911 ChumpCar endurance racer - featured in May-June & July-Aug 2016 Classic Porsche |
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Join Date: Mar 2004
Location: Snohomish, Wa
Posts: 365
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I had that question as well sometime back.I have a 77 911 decided to go with 2.8 P and Cs from JE ported exhaust to 37mm the docs e grind cams tall pmo manifolds with webbers.
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