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Posted: Jun 11, 2009 8:28:48 am
Pete



I thought we needed a thread on camshaft options and choices. camshaft selection is a black art as far as I can tell. The choice of camshaft profile really will more than any other modification define the character of your car.  For example the early 'S' cam profile makes the early 911's very revvy and produced all their real power at the top end of the rev range.  This is fine is you spend you time flat out everywhere, but not the most convenient characteristic for daily driving.  However, the same cam on a 3.2 carerra will not produce such a peaky power delivery.

post here about your experiences of cam seletion, including reasons for choice, expected change and what you got in eventuality, power gains and power delivery etc.

For my part, I chose a Porsche 911 GTII profile.  Yes thats a profile for a turbo car and mione is naturally aspirated.  That doesnt matter - I chose the profile because the lobe centres were similar to a 3.2 profile helping to avoid iverlap and reverberation, but they also had high lift and log dwells.  I still had overlap, but not as much if I would have gone for lobe centres close to 100 rather than 112.  This means I gained a power deliver curve that was continuous accross the rev range as you can see from my dyno below.



The cam selection was also dependent upon piston pockets and timing.  The 3.5Mahle pistones have the deep pocket to give you more valve clearance and the lobe centres and dwell let you work out the phase shift between the piston sine wave and the valve sine wave and there if you are going to get any overlap and pistons colliding with valves.....

Here's a list of some of the early air cooled Porsche 911 camspecs to help make the choice:



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