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Valve Clearance Between Piston
Does anyone know what the valve clearance should be between the intake & piston and the exhaust & piston when in time? Been having issues with cam timing and was just wondering what a safe range would be.
Thanks 2.7, 8.5 to 1 compression, SS grind on cams |
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11-24-2009, 03:41 PM
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Join Date: Jul 2001
Location: Wilmington, NC USA
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I don't know how you can run a CIS piston with S cams. There is practically no valve cutouts on CIS pistons. I don't know how the valves are not hitting the pistons. Normally an S cam timing is a 5.5mm overlap(if memory serves). CIS cars are about 1mm overlap. CIS does not work well with big overlaps so most people convert to carbs to run hotter cams and pistons. Have you changed pistons along with the cams? If not be very careful.
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69 911 2.3Ez 85 928S |
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11-24-2009, 04:22 PM
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One of my thoughts is to have valve pockets cut into the pistons. Any thought on that?
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11-24-2009, 04:39 PM
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AutoBahned
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buy the right pistons
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11-24-2009, 04:58 PM
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Quote:
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Recording Engineer, Administrator and Entrepeneur Designer of Fine Studios, Tube Amplifier Guru 1989 Porsche 911 Carrera Coupe 25th Anniversary Special Edition Middle Georgia |
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11-24-2009, 05:00 PM
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What are the right pistons?
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11-24-2009, 05:15 PM
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Get a set of Carrera RS pistons and cylinders. They are available both new and used. I see them for sale on here for reasonable prices all the time.
-Andy
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72 Carrera RS replica, Spec 911 racer |
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11-24-2009, 05:35 PM
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In my 69 I installed JE Forged pistons. You can order them to the compression ratio you want and with cutouts for the cam you are using. They were about $900 for the set but that was 8 years ago. It was interesting because the JEs were lighter than stock Mahles by 22 grams per piston. That's a lot of rotating weight to loose. The advantage with JE is you can design the engine to a custom set up if you want. Have fun. Here is a pic of may old girl at the track.
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69 911 2.3Ez 85 928S |
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11-24-2009, 06:21 PM
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Looks awesome!
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11-24-2009, 06:36 PM
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First, did you mean an S grind? as you said SS, second, are you still running CIS? If so you can only upgrade to a mildly hotter cam without affecting the operation of the CIS
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Robert Currently Porsche less (but the wife has 2) |
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11-25-2009, 12:59 PM
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I did mean @ grind sorry for the typo. I have since located a set of Porsche 2.7 RS Mahle pistons and went back to my original Solex cam configuration. So I do have the brand new set of 2.7 8:5.1 CIS Mahle Piston for sale if anyone is interested! Thanks for all the input, it helped me do the right thing.
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11-25-2009, 01:58 PM
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Thanks RWEBB, short and to the point advise.
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11-27-2009, 08:53 AM
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1968 Porsche 911T
1986 Porsche Carrera
