4R magnesium case for a 2.8 rebuilding project
 

Hey guys,

I’m starting to rebuild the engine of my 2.4S with a QSC/JE set of 92 mm bore and compression ratio 10.5:1 and twin plug ignition.

Unfortunately, the case of my engine is a 4R magnesium… and I am afraid of issues of the case, although the car is only for street use.

Do you suggest to me to abandon the rebuild project? …or modify the project, lowering the compression ratio?

Thank you in advance for your help.

I may be wrong, but for the money you spend to make your 4R case 'right' you might be better off trying to find and prep and early aluminum or 76 Carrera/Turbo case. just my .02

The 7R mag case is another choice. The best of the mag cases and still affordable. You will still have to have the case worked over with the proper mods to withstand your 92 bore plan. If $money$ was not an issue, I would go for a 3.0 case and Henry's new 66mm crank.......... 66 X 95 sounds fun.

Were you budgeting for all the case work? If so and your trusted machinist gives you a preliminary yes to it being doable with your present case, wouldn't it be fine for street use? I would say, once the machinist advises, can better know what to do about your case.

Regards,

First and foremost, don't bore out a real 'S' case, especialy a 4R case. It isn't the right case for the job. Buy a 7R case and do the proper work to it.

What he said. Put your original case on a shelf and leave it alone. Buy another case to build on.

I have one of these but it was built on a ’73 7R 911S 911/53 case (sorry Kenik, I built this one about 1975). I didn’t do everything that I would do today. It has case-saver head stud inserts and oil bypass but not shuffle-pinned. It still has original MFI and Mahle Nikasil 92 mm RSR.

This has been in my ’70 914-6 since then. Well … not quite always. In about ’81 I was a “hired shoe” for a GTU RSR at the Daytona 24-hour. To make a long story short, they paid my way home and I brought this 6-year old engine (in 911 config.) back to Daytona as ‘excess baggage’. We ran the entire practice and 24 hours with it and ran as high as 7th overall. After a ‘maintenance overhaul’ it is still running today.

My upcoming ‘maintenance overhaul’ will include shuffle-pins and twin plugs. I’m going to raise the CR (now 10.6:1) to as high as possible. Everything else will still be original ’73.


Ennio, I agree with Kenik, use a later 7R case. Partially so your original ’72 4R case gets saved and partially because the 7R is a noticeable improvement in strength. You will probably find the best ones as ’73 2.4 911T (and ’73.5 CIS) because they had lower stress. You will need to do all the ‘improvements’.

You will also need to have the biggest front cooler up front. A fender cooler (even an original ‘72S) will benefit from an electric fan. Critical will be the 1.82:1 engine fan from a ’75-> Turbo.

I use 112 octane leaded race gas. You should consider your fuel source when deciding CR.

Best,
Grady

I have a 1977 911/85 7R case for sale. There are two gents interested in it , but no firm offers to date....interested????


al

Dear friends,

thank you very much.