Engine case 7R in a USA MFI T/E.....what do I have??

[BOYER73S]

I have a question re when Porsche stopped using 5R cases for USA MFI T/E cars and started using 7R cases?

I have acquired an engine that definately has a 7R case, both halves, but is from a 73USA T/E chassis 9113110725 so one of the last of the MFI cars
before the change to CIS injection. Internals are 911/51.

I have an exact same car in the garage but chassis is an earlier coupe 0350and it definately has all the same markings except its a 5R case.

I thought all T's had 4R/5R cases even the MFI ones.

How come this one is a 7R case and yes its original to the car for sure?

[letsrollbabe]

Clyde:

I think this is pretty good proof that there were few 'absolutes' at the factory in the early 70s. Whenever I hear someone make a definitive statement about what the factory 'always did', a little smile appears on my face knowing that it will most likely prove incorrect. Congrats on finding a 7R case for your 2.5L engine.

[MTemp]

I am dismantling a 73 2.4T (US) engine for a friend and it also has a 7R case. In the discussion on DDK it seems this is not that uncommon, although the spigot size on these 'T' 7R cases is often 90mm (as in my friend's case ), not the 92mm (?) in the later 2.7 cases. So it seems not all 7R cases were created equal……

Check which one you have…….

Mick

[letsrollbabe]

I think the 2.4L spigots are 92 mm and the 2.7L spigots are 97 mm. The 2.5L long stroke ST engine used 86.7 mm P/Cs and they require 94 mm spigots, so that is why only the 2.4L 7R cases work. For a short stroke 2.5L engine, many guys go with a 90 mm P/C set, and the stock 2.7L 7R case works for that application.

[davep]

Any transition cases should be added to this thread; serial, type, revision # from both sides, date codes if found, photo documentation really helps.

http://www.early911sregistry.org/for...case-Revisions

[2.5MFI]

Good find Clyde, I also have a 73 T engine s/n 6133470, internals 911/91 with a 7R case small spigot's.

[letsrollbabe]

I too have a 2.4L 7R case 6135015 built for a 911/91 CIS second half 73 car. It will be used with a set of 86.7L ST P/Cs to build a 2.5L long stroke engine. The 86.7 cylinders are the first factory use of Nikasil cylinders for a 911, derived from their successful use on the 917s. I believe all the earlier ST engines used Biral cylinders, including the short stroke 2.5L versions.

[panama911]

Mark,

I have two Mag 7R cases, both 911/91 (73.5 2.4T CIS small spigot).
One ist s/n 6133469 (original to my car, looks like a direct neighbour on the production line to yours, Mark!)
BUT the other one is stamped 6135945...
What does this mean? It's the high number that makes me wondering... may it be a factory replacement case or something?

[davep]

911/91 went from 6133001 to 6136092 so 6135945 is okay, just late.
On the early engines watch for 5R/7R as a transition case; just cause it says 7R on one side...

[MTemp]

I think the 2.4L spigots are 92 mm

Case 6135494 are 90mm.

Mick