What's so special about a 7R case?
 

I've got a 2.4CIS that is a 7R case (73.5). Why is the 7R case so desirable? If I'm running CIS does it really matter what case I have/use?

The 7R case contained stiffening ribs and thicker walls (in some areas) than its predecessors.

These changes made the 7R a better candidate for larger-displacement, high RPM engines.

The 73.5 7R case is special because it has all the benefits of the stronger 7R case like Steve said but it also has the smaller spigots for the cylinders. In 74 they went to the 90mm pistons and opened up the spigots. So anyone that wants the stronger 7R case to build a 2.2 or 2.4 engine would want your case.

Yep - matter of fact Steve just did my small spigot 7R for a 2.3L ST motor I am building. This case was the best choice bassed on weight and the fact it has accomodation for an MFI pump (the early aluminum case doesn't - and it is heavier).

That's the same case my 2.6 is built on.

Just running it for the first time this week.


KT

Here's some pics showing the differences in the case structure between a 7R and an early mag case.

Note the extra reinforcing ribs in the 7R.

7R

http://forums.pelicanparts.com/uploa...1237283387.jpg

http://forums.pelicanparts.com/uploa...1237283447.jpg


Early Mag Case


http://forums.pelicanparts.com/uploa...1237283555.jpg

http://forums.pelicanparts.com/uploa...1237283598.jpg

is there a way to reduce the spigot diameter on a 74-77 7r case? i would think a sleeve would work. there is a set of 86.7mm st cylinders on ebay that require an odd size spigot - it would be a good use of a later 7r case i would think.

Yes - Supertec offers a kit for this. It involves spacers, aerospace adhesive and some special sauce.

The other benefit of a 2.4 7R case like yours is it came off a car that did not have thermal reactors. Most of the later 7R cases used for the 2.7 liter mid year motors had thermal reactor in the exhaust, which led to higher motor operating temperatures, and more sever heat cycles for the case. This leads to faster wear and fatigue for the magnesium.


Or so I have been told.....

4/5R is real close also, just missing the lower vertical gussets.