74 Carrera Coupe Resto

[MountainRoads]

you want this . . .

FWIW: I agree with Scott and the other MFI advocates. MFI is much more "period correct", especially if you are going with a larger displacement engine in a '74, anyway. You're dumping enough $$ into this engine that I doubt cost differences will be a factor. True - CIS will give you better mileage, but is that really important in a car like this?

- MR

[rynoshark]

When you rebuild , since you have an early 1974 . You will have a motor that originally (if their still there) came with special Nikasil CIS Cylinders. If you need to replace , make sure you get the same...not the later Alusil cylinders.

When exactly was the switch from Nikasil to Alusil? I haven't been able to track this down anywhere definitively, but I may not be looking in the right places!

[MountainRoads]

Something else to consider in this debate. I spoke to friend yesterday who has a '73.5 (??) T with CIS, as well as a couple of earlier longhoods, one of which he races. In chatting, he commented that the CIS was very "drivable" in-city and with gobs of torque, but started to run out of breath at about 5K RPM, which is exactly where MFI and carbs would start to show their stuff. (Yes, I know there are other factors, as well.)

Although not having to work the gears as much has it's plusses, you also lose a little bit of what these cars were to drive. The point is you have to decide which of these attributes is most important and base your decision on that. My additional .02.

- MR

So

[Fidalgo911]

Above 5k rpm is exactly where SC cams give a CIS car more life. I had stock cams on my '74S and it fell off a cliff at 5K (same motor as the '74 US Carrera). With SC cams it pulls hard past redline.

Something to think about.....

[peekaboo]

When exactly was the switch from Nikasil to Alusil? I haven't been able to track this down anywhere definitively, but I may not be looking in the right places!

rynoshark ,

I'm sorry if I cannot get any more specific. I just know I have had this bit of info. stuck in my brain for a long time. Someone told me or I read along time ago. That the very first 1974 CIS 2.7 S models (I don't know about the normals) had nikasil cyl's . It is probably not chronicled by serial number by the factory (well , it MIGHT be somewhere...buried in some factory archives). It was a cost factor deal. And I would think the piston for each was differant (CIS alusil & CIS Nikasil) . But I am not certain of this. Maybe just the rings.

I'm sure someone out there , knows something about it. Try a post on the Bird.

[Flieger]

The pistons are definately different. Alusil cylinders are considered "soft" and need a "hard", iron-coated piston. Nickasil cylinders are considered "hard" and need a "soft", Aluminum piston.

[RSTarga]

nikasil started with the 2.7 carrera rs although supposedely some 2.4 engines came this way although i've never seen one. I've driven a 3.0 CSI car that I would have sworn was a MFI motor, very trick high compression motor. I think the best route would be 2.7 RS spec with MFI. That would be the same as a european 74 RS.

[letsrollbabe]

The 2.5L ST MFI engines had nikasil cylinders, which I think were the first for a 911. Nikasil had been used on the 917s, so in 72 when the factory needed a larger bore to get nearer to the 2.5L limit for 911 circuit work, they used 86.7 mm alloy pistons with nikasil cylinders.

Yes, Peekaboo, many (if not most) 74 CIS cars came with nikasil cylinders, not sure when the factory switched to alusil, maybe 75 MY.

[peekaboo]

I don't know what makes a 2.5 dispacement vs. a 2.4 , but in searching for 2.4 Nikasil cylinders with pistons. I come up with some available :

A set of 6 / 911.103.944.01 (noted as Mahle 2.4 911S , nikasil ....from a non-factory supplier). But then another non-factory supplier lists this number as ONE 2.4 911S Mahle Nikasil barrel & piston assm.

Then there is the PET listing of this number 911.103.944.02 (which is noted as one / six required) ..with no notation other than 1972 - 73 911S (Mahle as 'Schmidt' is not noted).

So are stock 2.4S barrels nikasil ? (I had always assumed so , but now i'm thinking not).

[Chuck Miller]

So are stock 2.4S barrels nikasil ?

No, they are biral iron........

I learned the stock 2.4S piston set that came out of my '73 weighed about 12 lbs. more then the 2.7 Mahle Nikasil RS piston set I put in.