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Registered
Join Date: Sep 2002
Location: Stellenbosch, South Africa
Posts: 888
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Camshaft profile grinds
Guys
please excuse my ignorance, but I have to learn. How is it possible to achieve a different profile with higher valve lift or longer open/close duration on a cam lobe if all you can do is remove metal (i.e. "grind") from the lobe? I guess I understand how the different profiles from say the 964 or 20/21 profiles could influence the breathing characteristics of an SC motor. Is metal welded onto the lobes prior to grinding the new profile? If so, how is lobe wear influenced? Regards LeRoux
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'90 964 C2 coupe (sold  )There are no old Porsches, only new owners. |
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02-18-2003, 03:54 AM
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Registered
Join Date: Jan 2002
Location: Long Beach CA, the sewer by the sea.
Posts: 37,700
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They grind all the way around the cam reducing the base circle (the round part opposite of the lobe). The cams are treated afterward. Not heat treated IIRC, because that apparently can warp the cam.
So, simply put, if you reduce the base circle by x amount and knock off the lobe by 1/2 x amount you increase the lift by 1/2 x amount and increase the duration beacause the lobe is less of a peak. In a push rod engine, often times you need a longer rod to compenste. |
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02-18-2003, 05:53 PM
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Senior Member
Join Date: Jan 2001
Location: Left Coast, Canada
Posts: 4,572
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'81 SC Coupe "Blue Bomber" "Keep your eyes on the road, and your hands upon the wheel."- J.D.M. |
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02-18-2003, 07:18 PM
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