All Porsche cam chain tensioners are hydraulic. They all use oil to dampen the spring. The spring is what does the actual tensioning. The difference is in where the oil comes from. Some just have a one-time fill of oil while Carrera style get a constant feed of pressurized oil.
"Mechanical" tensioners commonly refer to the solid metal ones used for setting timing.
The safetry collars only work on non-pressure fed tensioners. There is a mod that involves cutting a length of rod to fit inside the pressure-fed ones so that it acts as an internal stop. "Jerry Woods mod" would be a good term for searching.
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened
Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
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