When was the 7R Case Introduced?
 

I have a 7R case from my 1973.5 911T that I am planning to offer for sale in the classifieds. In Wayne's book he says that the '73.5 case is the only 7R case manufactured with the 92 mm spigot diameters and that it was produced only for 6 months before the spigot diameter was increased to 97 mm. This is supposed to be the best case for building race engines at 2.4 liters and below. The engine type number for the 1973.5 CIS engines is 911/91. This matches the number on my case as expected.

Recently there was another of these 7R/92 mm spigot cases for sale on Ebay with the type number 911/52. This type number is listed in Bruce Anderson's book as the number for the '72/'73 911E mechanical injection engine. The photos showed the extra webbing on the outside of the case near the flywheel, the 92 mm spigots and the casting number 901.101.101.7R indicating that it really was a 7R case.

My question is....Was the 7R case with the 92 mm spigots introduced only for the the last 6 months of the 73 model year across all of the engine models (T, S and E)? Or was this case introduced earlier and produced for more than the 6 months reported in Wayne's book.

I know this is somewhat of an arcane question. However when I offer my case for sale, I want to be able to correctly represent it.

Hi Tom.

From what I have heard, there wasn't a specific "cut-over" to the new cases from a certain engine number. The situation was more like, "vee haff zee new shtarker cases at zee back door, vere should vee put zem?" And they started using them when they ran out of 5R's. So I would think it entirely possible that an MFI motor could have been built with a 7R. I have also heard of a CIS motors being built with a 5R.

Anyway, I wouldn't be concerned about your ability to accurately represent what you've got. . . a 7R with 92 jugs. If I were a potential purchaser, once I had satisfied myself with photo of the engine number stamped on the case, I would be concerned about condition: roundness of the main bearing surfaces, condition of studs, open squirters, etc. rather than production volume.

No doubt someone will chime in with an EXACT cutover date now . . .

My Jan. 1973 production 911E has a 7R engine case.

This is pure supposition on my part but I think that the 7R came about because of the plans to build the 2.7RS, once that need was fullfilled and the 5s used up then the 7R was used for other motors.