Nobody ever talks about 5R cases, Differences between 5R and 7R ? Options

[michel richard]

Whenever a discussion comes around as to which /6 engine case to use for a high peformance engine, the talk always revolves around the early aluminum case, the early mag cases or the 7R cases.
My 2.2 E is built on a 5R case, which is the case that was used for most 2.4 engines, including most 2.4S engines, I believe.
I've never done a detailed side by side comparison of 5R and 7R cases, but I could'nt see differences between a 5R in my hands and pictures of 7R cases. I could see a number of differences between 3R (early mag) and 5R, however.
And I did have to get creative to fit the 2.2E distributor to the 2.4 case (the hole was too big, and the locking mechanism different).
So what is it? Do people forget the 5R because it's close to the 7R, because discusssions have just not gotten around to it ? because it's a little rarer ? or another reason ?
I'm asking because I'm beginning to contemplate a short stroke 2.5 project, and I would really like to keep my case.
The advice is often: go to a 7R, it'll end up cheaper etc . . . But I had to go through 4 cases before finding the one I have - finding good cases is harder when you're not in California, so that starting with a known quantity is a definite plus.
So, the question really is: can anybody help me figure out what the differences are between 5R and 7R cases ?

TIA
Michel Richard

[TimT]

I believe the only real difference between the two. Is the 7R is more heavily reinforced than the 5R. Additional reinforcing webs were cast into the flywheel end of the 7R case, also the main bearing webs were more reinforced

[davep]

We need to find some photos of the 5R case to compare with. Internal, external and flywheel end. Some of the changes are subtle, others are very obvious. Clearly, if you don't have a 7R case then 5R would be the next best one to choose. The 7R case was introduced as a running change in the late 2.4 production.

[carr914]

Some of the difference that I found out doing my 2.5 was that in addition to the reinforcement, the 7R didn't need to be machined to accept the 90mm cylinders and the oil squirters didn't need modification. I found a 7R case cheaper than the machining costs.

T.C.

[carr914]

And the other case is now a coffee table.

T.C.

[ArtechnikA]

yes - and those 92mm-spigot '73.5 7R's are pretty highly prized by guys trying to build up HiPo <2,7 engines...

there are many guys on the Racing List who actually prefer the 5R - or even the 3R cases. all the cases need prep machining, and they're all a bit fragile when pushed to the edge, so (as their thinking goes...) you might as well start with one that's had a much easier and less stressful life as a street engine.

i think the point of diminishing returns hits with the 1R (i think it is...) that was the first case to have piston squirters. IMO these are essential, and are simply nonnegotiable for any Nikasil P&C.

it will cost a bit more to have 3R or 5R cylinder spigots opened up to 97mm like the '74+ 7R's but it's a drop in the bucket to the full cost of a race-prepped engine... and that presumes you're building a 2,7 or a 2,8. if you're building a <2,5 you want the 92mm spigot case, and if you're going bigger, you should be starting with a 3,0 SC case...

[lapuwali]

This advice seems to be repeated every time someone starts discussing Sixes in detail: get Bruce Anderson's book! There are photos in there of the 5R and 7R cases showing the differences. The 7R was, as Tim said, reinforced with extra webbing. If you're making a short-stroke engine, I'd assume that's to get more revs, in which case more bottom end strength would be a Very Good Thing.

[michel richard]

My 5R is in the car. I looked through my computer, but I could'nt find picutres of the inside of the cases. I'll look again. Once again, if I had both a 7R, especially from a 2.7, and a 5R sitting in my garage I would undoubtedly use the 7R. If the only machining operation I need is to open up the cylinder spigots, and if I can determine that a 5R is not materially different from a 7R in terms of strength, I may well keep my cases if I go forward with the 2.5 short stroke project.

I have a feeling that most of the strengthening was done between the 3R and 5R versions, not between the 5R and 7R, and I'm trying to find confirmation for that.

Michel

[ArtechnikA]

many internal photographs of 7R's in Anderson, donno where i'd find a 5R internal photograph (Frère?) but i'll poke around... for sure i have no 5R's around or i'd just photograph one for you...

[michel richard]

James,

I have the second edition of the BA book (second edition) in front of me, and I can't find a picture of the 5R case, or a discussion of it.
Please point me to the page !
Michel

[ArtechnikA]

there is an image of the flywheel area webbing, but nothing of the inner main bearing web reinforcements that were supposedly new with the 7R.

[michel richard]

Ok,

Found some pictures of the inside of my 5R case, but they don't show much, as far as the case is concerned.

[michel richard]

No 2

[michel richard]

No 3

[michel richard]

oops

[michel richard]

No 4

[michel richard]

And one of the fan end:

[J P Stein]

I compared the 2 side by side.
Tim is right, the 5R has the stiffening at the flywheel end, but not the internal bracing. The 5R also has the thicker spigots that the 3R doesn't and will thus take the overbore that is marginal on the latter.

The later 7R (76 & up) has the oil bypass mod built in and the larger scavenge section oil pump.....HP builders save money there.

Got to rootin' around in JimCs' new car/motor this morning, but I'll let him tell ya about it.

[Cap'n Krusty]

Tell me that's not gorilla snot between the case halves ......................! Shudder! BTW, I have a nice clean 7R case that just happens to be for sale ........ The Cap'n

[ArtechnikA]

QUOTE (Cap'n Krusty @ Jun 18 2005, 05:05 PM)

BTW, I have a nice clean 7R case that just happens to be for sale ...

92mm (73.5) or 97mm (later) spigot bore?
i'm set with a 92mm case for building up the 2,2 - but someone looking for a case will want to know...