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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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Old 05-02-2009, 05:00 PM
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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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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
Old 05-02-2009, 05:35 PM
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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.
Old 05-02-2009, 06:14 PM
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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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Old 05-03-2009, 06:30 AM
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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.
Old 05-03-2009, 07:19 AM
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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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Old 05-03-2009, 09:47 AM
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Yes it is a 2.7. Thanks for the advice.
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Old 05-03-2009, 10:31 AM
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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.

Old 05-03-2009, 11:28 AM
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