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I have a 71 911S with 2.2 Engine that was rebuilt a few years back by a previous owner. In reviewing the rebuild records and receipts, it says that new pistons were installed during the rebuild with the notation "911E lower compression" Does anyone know why 911E pistons would be used instead of S pistons?
The 2.2 S had a pretty high compression ratio. That was fine in '71 when you could pull into a chevron station and buy high octane "white pump" leaded. Not so fine with today's unleaded "reformulated fuels". I suspect the move to lower compression was for that reason, so the car would run on what is called gasoline these days. Also why Porsche lowered compression & increased the stroke when they came out with the 2.4 engine...in order to run on the lower octane fuels that they knew were coming. IN the long run, whoever rebuilt with the lower compression in mind may have done you a favor?
The "S" cams would not clear the pistons if the pistons used were "E" type. The piston to valve clearance is .040" (one millimeter) in an early 911S. For the intake valve the closest interaction appears at 5 degrees before TDC. For the exhaust side the closest interaction is 5 degrees after TDC, again clearing by .040". The E piston does not have a big enough eyelash cut to accomodate the valve. So the question remains: what cam shaftsd were used?
Hmmmmm? 2.2 or 2.4? S or E cams? I wanna know more...not being facisious here. I really wanna know more.
I mean, Bruce Anderson expressed concern about 2.2 pistons being used in a 2.4 to increase compression, BECAUSE OF VALVE CLEARANCE PROBLEMS. But, assuming that E's ran lower compression than S's (this true or not?) Why would E pistons do anything more than lower compression? I'm sincerely curious here...