I have limited knowledge and zero experience with the 911 aircooled engines, hence the question. Some background info to put things into context. The other day I came across a 914/6 engine. Visually the barrels looked a bit big to me so the owner measured them with his calipers and came up with 89.86mm. That would make it an engine around 2.5L.
As I think, 914/6 engines use the 3R magnesium case, then to me a 2.5 that spins up quickly with the standard crank is not the best idea, especially if other mods like cams and cylinder heads help it produce more torque at higher revs. So, short of using a 7R case, aluminium cases seem to be a good idea for longer lasting engines if you don't mind the extra weight.
That leads to my two questions-
1. What aluminium cases accept the short stroke 66mm crankshafts from the 2.0L?
2. Which of these, if any, allow for a direct swap of all the engine components from a 914/6 engine?

As far as I know, the early 65thru 67 sand cast cases and the 3.0 case from a early 930 turbo or early euro careers, all very expensive and rare now, do you ever go down to the white star for a pint

Thanks for the reply.Have had a few there Sounds like you've had the pleasure also.

I believe their are two companies currently working on making new 911 AL cases. Can't find them in my bookmarks at the moment but I believe there was a thread on Pelican about one of them.

One is a member here - Catorse. He's making 3.6 cases and is in production now. I believe they start at $6,500 and look fantastic.

@Catorse

A 7R case is really nothing special. Some more webbing for some extra reinforcement but still a 40 year old mag case.

All the early 911 engines had aluminum cases.
All were 2 liter. That changed somewhere around 1967.
You can have an early case cut to hold 2.7 cylinders and will have
a short stroke 2.5. If you use the early 2 liter heads,
they need machine work also.
Very early 930’s and probably Some other very early 3.0 engines could
also take the 66mm crank and get you a 2.8 short stroke.
Both options are pretty expensive and the early 2 liter cases also
need some upgrades like oil squirters and some oil passage work.
You could also put a 66mm crank in a mag 2.7 ....
I imagine all the parts fit but I don’t know anyone that has actually done it..

68 alum. cases use the later style chain housings.. late 68s are mag case

For a street engine, a well prepared mag case that was in good condition can serve quite well. Agreed that they are not as good as Al cases, and they require some fairly extensive machining, but they are available and will do the job. There are lots of them out there doing their thing.

Unless you are connected or very lucky or willing to spend big, good luck finding an early al case. That leaves the early 3.0 cases.

Yes an Al case short stroke 2.5 is one sweet piece. In my mind pretty much the epitome of porsche aircooled goodness in a 914. A mag case one is not far behind. Good luck

the early aluminum cases with small (stock) spiggots will definitely work and will hold their machine prep.

but they are much much more expensive due to the fact that everyone has known they are stronger for the last 50 years.

Around 1977, I bought a very early 911 engine for 500.00 .
I put it in my car and put my original engine away .
Somewhere in the early 80’s my friend and Mechanic
saw a write up about the 2.5 SS engine and decided
he wanted to build one.
He was the engine builder for Ralph Meaney when Ralph
was based out of Massachusetts.
He took the 65 engine out of my car and built it into the 2.5
and didn’t charge me anything ...
It had 2.7 S mechanical injection pistons and cylinders and
real, center oil solex cams..
It really made the car fun to drive..
It had a set of racing headers, a backup set from Ralph’s stash
of GT parts and 2 resonators but no mufflers.

Needless to say that selling that engine funded
my car being stripped and painted a few years ago...

I've sold a couple. $7-12K for a case isn't unusual but sometimes people will pay more if they need something specific. Sold a "64 case for $35K plus some stuff in trade.

I think it's worth the money because they hold their value or go up. You get back the money when you sell. You don't really get back the money you spend on machining a mag case. But there are reasons for using for both types.

I have one.
it was built by Supertec
then I ran it 5 seasons

its tired and needs a rebuild
2.0/6 parts, heads, etc

65 case with 67S guts

and I found the owner of the car on the east coast that has the matching vin.


they are not cheap
Mine is worth 10k.. or more to the car owner
I have come down in price yet.

brant

Generally, matching numbers are good for a 15-20% bump so I bet it’s at least 10k.

What is the intended usage for the motor. IMHO, if you are not racing it you may be
over-analyzing this. How many miles a year are you going to drive it and how many
will be full-throttle high revs anyway? Don't spend a ton for the strongest case if the
life you gain is 20 years from now anyway.

You could refresh the current setup as 2.5L, or you can get AA 86mm fairly cheap and
go for 2.3L (I can't recall but may need different heads). Plenty of power on a 914.

[/quote]
Generally, matching numbers are good for a 15-20% bump so I bet it’s at least 10k.
[/quote]

That’s why my original engine will sit on the shelf and never be put back in the car in my lifetime....
I have a different 914-6 case with 69 S pistons and cylinders and solex cams
that will be available when needed...

Good point about resale/ retained value Mark

I also believe that you can over build over think these things. My car is a toy. Maybe 2000 miles a year. If it goes good for 10 years I think I will be a happy camper. I do not get in the car for an evening drive and worry that my mag case is gonna fail

Ther.e may be some value for some in being able to say they are running an AL case, but I ain’t that guy.

Just gathering information, over-analyzing comes later! Does 80,000 km over 20 years with spirited driving at times sound ok? We have been promised a motorsport complex here so I wouldn't race but would give it a go on track days.
When I came across the engine I expected it to be standard. I have a '72 914 with sideshift and have recently acquired a 914/6 front strut assembly, hubs etc. I could continue to "914/6erise" it.
Thanks for the responses, I think the answers to Q1 are pretty clear.