2.7 magnesium case

[seafeye]

Is there anything special you would do when rebuilding a 1975 911s magnesium case engine?

The car has about 125,000 miles. Would you replace pistons/cylinders for a more modern design? Wouldn’t mind more power. But nothing crazy.

Modification Suggestions?
Strictly street driving.

Thx.

[Flat6pac]

You need to completely disassemble and case saver the 24 studs.
There is no limit the money that could be spent, inquire the knowledgable people.
Bruce

[SiracHaile]

I recently had my mag case machined. There was many things I did to ensure it’s a solid case. But if your bottom end is fine a top end is okay, but the head studs may pull threads.

1. Case inserts on head studs and other critical areas
2. Check align bore and machine back to standard
3. I spot faced all the sealing surfaces
4. Oil bypass mod and update the pressure valves

That would cost around 1500-2000 just for machining. I had a lot more work done but I would think the above is the minimum.

[Gonbad]

Contact William Knight aka Knightrace on this forum. He will put you were you need to be within your budget.

[chrismorse]

Those of us with Mag engines will need a bit more corrective machining and updating.
The lure of more HP is strong, but i would recommend caution, first going for cleaning, measuring, determination of substandard specs, flatness, parallelism, warpage, pulled threads, clearances, valve guides and valves.
Don't forget budgeting for ancillary things , WHILE YOU'RE IN THERE , Clutch, Starter, Alternator, Hoses, wiring repairs, motor/tranny mounts and miscellaneous cosmetic stuff like new zinc hardware.
Once you know how much it will take to put things back "right", then you may consider bumping the compression, EFII, ITB's, bigger oil pump, bypass mod, cams, porting,
Given the delicacy of the Mag case and its fragility, i would first, on my mod list, go for a carrera front fender cooler, to keep the temps under controll.
For example, my dad's 74, with dealer installed AC, and no external cooler, ran absolutely scary termperatures, like 240, just cruising, in santa barbara - not geting on it at all.
The first thing i did when he passed the car to me was the cooler update. Subsequently, with cooler temps and a bit more oil presssure and "spirited driving", the thermostat in the case popped out of the block, with pulled threads
Spend on the side of caution and durability.
Bon Chance,
chris

[seafeye]

Thank you for the responses.

[Walt Fricke]

The desire for more HP for street driving has always mystified me. I know it exists, because it is so often discussed. And like most of us, I am a product of my experiences. I moved from 1200 and later 1600 VW Beetles, and a 1600cc Bus, to a stock 1977 911. Good grief - what a difference. There were uphill curves in the mountains I actually had to slow down for. Plus I had heat on the downgrades.

This was during the national 55mph speed limit. The 911 was hard on my bank account due to speeding tickets, though thankfully my state ignores tickets from other states.

There isn't really such a thing as a more modern design for pistons and cylinders, though if yours are worn out, Charles Navarro's Nickies would be worth investigating - these cylinders have more cooling fins. Unless you change away from the CIS fuel injection system (which works fine on a stock engine) there is no advantage to some other piston design. And you've got to be careful about compression boosts, as you can't get 93 leaded as you could in the '70s.

Improved oil cooling is for sure the way to go no matter what. Hard to have too much of it.

Now my street car is an 07 Turbo. I won't donate it to anyone, but it has way more power than I can use.

Is there some specific situation driving around where you feel your '74S lacks the power to do the job?

[Henry Schmidt]

Originally Posted by Walt Fricke

The desire for more HP for street driving has always mystified me.

In a world that produces 1200 horse power street cars, there shouldn't be that much mystery.
Avoiding the whole phallic symbol analogy, horse power is a drug. The more you get the more you need.
High caliber firearms, the biggest boat, the swankiest house. It all feeds the ego.
With sports cars, more horse power equals more "sport".
The mid 70's 911 are some of the most disappointing Porsche engines. They were caught in a smog transition and a fuel "crisis".
Although they are certainly driveable, the factory built in too many compromises.
The biggest is probably compression. They advertised 8.0:1 for the normal and 8.5:1 for the "S" and in actuality, 7.5 and 8.0 are more accurate numbers. Add to an absolute lame cam and what should easily produce 200hp is actually making 160.
As for "modern pistons" there are absolutely better piston designed than the squish camber non-sense of the mid 70s.
The removal of smog gear, slightly better compression numbers and a better cam the the lowly 2.7 can come to life.
The key then becomes: how do you keep it alive...that's a longer question for another time.
Cheers

[Bend911]

Originally Posted by chrismorse

Those of us with Mag engines will need a bit more corrective machining and updating.
The lure of more HP is strong, but i would recommend caution, first going for cleaning, measuring, determination of substandard specs, flatness, parallelism, warpage, pulled threads, clearances, valve guides and valves.
Don't forget budgeting for ancillary things , WHILE YOU'RE IN THERE , Clutch, Starter, Alternator, Hoses, wiring repairs, motor/tranny mounts and miscellaneous cosmetic stuff like new zinc hardware.
Once you know how much it will take to put things back "right", then you may consider bumping the compression, EFII, ITB's, bigger oil pump, bypass mod, cams, porting,
Given the delicacy of the Mag case and its fragility, i would first, on my mod list, go for a carrera front fender cooler, to keep the temps under controll.
For example, my dad's 74, with dealer installed AC, and no external cooler, ran absolutely scary termperatures, like 240, just cruising, in santa barbara - not geting on it at all.
The first thing i did when he passed the car to me was the cooler update. Subsequently, with cooler temps and a bit more oil presssure and "spirited driving", the thermostat in the case popped out of the block, with pulled threads
Spend on the side of caution and durability.
Bon Chance,
chris

+1 on the cooler. I have a 1975 S and that car ran high temps without a cooler. I could only drive the car in the early spring and late fall because summers in Central Oregon were too hot. The first thing I did was install the Elephant Racing cooler. The car now runs ~30 degrees cooler all of the time.

[Jeff Alton]

Originally Posted by Flat6pac

You need to completely disassemble and case saver the 24 studs.
There is no limit the money that could be spent, inquire the knowledgable people.
Bruce

^^^^^ As a start...

Have the align bore checked and corrected if required (likely), truing the spigot surface etc... And if going after some power, consider dowel pinning the mains at minimum...

[r lane]

An aluminum case is optimum, but you can make the mag case work if oil leaks don't bother you, but the expense may not warrant it. Bore the mains as the case becomes a banana, heli coil or time cert the studs, deck the spigots and shuffle pin the webs. I took the worst 2.7 case I had ever seen and turned my 72 into a 2.7, 9.5 to 1.0, MFI and S cams, (did not want to bore my original case for the larger cylinders). That was 20-25 years ago, drive it most days. It is getting to be a bit noisy now and the case may be nearing its end, but I am not mad at it, has been a great engine. Bob

[PeteKz]

Considering the amount of work most 2.7 cases need, I decided to just go with a core 3.0 SC engine years ago. I'm sure it saved me money and built a much stronger engine.