Edgy01

Finally, after all these years, I finally figured out the real reason that Porsche stuck to magnesium case engines before moving onto aluminum. Of course, Porsche was always telling us that it was all about saving weight and all that good party line...

Here's what I learned in some of my metallurgy reference books:

(1) It takes 50% of the time to cast a magnesium casting than an aluminum casting. (less production time= less $$)

(2) The molds for casting magnesium last longer than the molds for casting an aluminum structure. Thus, you can create more magnesium castings for less...money!

As we really should have known,--it was all about money!

Brads911sc

couldn't it also be that they learned things over time and improved their design? did they also use inferior carbs in the 60's, inferior oil cooling in the mid 70's, inferior fuel injection in the 70s and 80s... inferior AC in the 80's, inferior headlamps, inferior targa seals, inferior tire sizes, inferior brake master cylinders... just to save money... i dont buy the cheaper argument. alot of what is on our porsches changed over time and improved along the way... Porsche's have always been 10x the price of the average car... its a porsche not a chevy...

r911

The company once had a nearly no amount of $$ is too much to make our car the best philosophy. P AG has always led in the use of exotic materials - Mg soft top bows (award-winning), Be in racing brakes, ceramic brake rotors, Al lug nuts, you name it. Now there is a letter in this month's Rod & Truck where a guy says they are crazy for saving 20 lbs. by using Ti in the exhaust system.

Lower cost may be one reason, but where did you find these data and were they true at the times the switches were made by P AG?

It appears they went back to Al when the Mg did not hold up - for both transmissions & motors.

Mike Murphy

The goal was to save weight. Both Aluminum and Magnesium can do the job, since they are comparable in density and strength. But Magnesium was cheaper to manufacture, like Dan said.

Mike Murphy

Right - performance was #1 goal. They saved weight. So if you could save the same weight, but there were 2 ways to go about doing it, which would you choose?

Houpty GT

Magnesium is stronger per pound than aluminum and is a higher performance material. Magnesium is more brittle though. I do believe that magnesium cost more than aluminum but I could not find any prices for you.

Mike Murphy

http://www.magnesium.com/w3/data-ban...&magnesium=202

Peter Zimmermann

Don't forget, early 911 engines were aluminum. The change to magnesium was driven primarily by the never ending challenge to save weight, evidenced by Porsche doing everything that they could think of to more evenly distribute the car's weight. They stuck lead weights under the front bumper/valance to improve balance, then they went to dual batteries in the forward corners of the car. They increased the wheelbase, I'm sure at great expense, all the while knowing that they had to improve the suspension, and at the same time they had to reduce the mass of the lump hanging out behind the rear axle. Many things in Porsche's history showed that they had no fear when it came to spending money developing their beloved 911. I think that the development of the 3.0 liter engine, with its wider spaced cylinder head studs and larger main bearing journals, was simply an evolutionary design dictated by need. Suspensions could tolerate the weight gain, internal engine strength became an issue, and the change was made. Magnesium had served its purpose during the small displacement era, and Porsche knew, as a 2.7 liter, that it had run its course.

theiceman

Yeah Baby ..... all hail the 3.0 litre ..

GothingNC

John

Mike Murphy

That's a heck of subwoofer you got there. I want one!

To answer your question, it's kinda like diamonds - one of the hardest materials, but if you smash it with a hammer, it will crush.

Houpty GT

No! The diamond will put an indent in your hammer! Diamonds are quite incredible.

Glass is very hard. If you punch a thick piece you will shatter your hand and you will not be able to bend it. If you hit it with a hammer at medium strength it may not leave any mark at all. Hit it a little harder and the whole thing will shatter. A piece of aluminum the same size will get dents in it from medium hits with the hammer and with a harder hit it will make a larger dent but will not break. You can bend the aluminum in half with a huge machine and it will stay intact even when folded. The glass would shatter under the same process but will require more force before it starts to bend.

Strong is how much it takes to bend and brittle is how soon it breaks.

I looked up a few numbers real quick of some die casting alloys. The aluminum alloy was 33% harder than the magnesium alloy. Magnesium weighs 35% less than what Al did for the same volume. For equal weights in mass, the Mg will require 40% more force before it will stretch but only 10% more force before it will break. Taking advantage of these numbers requires that you are only limited by weight and not limited by volume. So the Magnesium will weigh the same as the aluminum but will be larger. If you limit yourself by volume, as would be the case with the threads in a hole (head studs!), you will find that the aluminum is stronger and heavier (steel would be even stronger and heavier).

Peter Zimmermann

A good analogy is that the aluminum crankcase is like uncooked pasta, while the mag case is al dente. In 1969 engine weight is stated as 176 kg (388 lbs) for a 911T w/carbs. That compares to a '68 911 (T,L or S) engine that was 184 kg (406 lbs). Even the first engines fitted with the heavier MFI system were lighter than an aluminum engine w/carbs, tipping the scales at 182 kg (401 lbs) for both the E and S. The lighter weight, combined with no perceived downside, probably made perfect sense to Porsche, so they switched to magnesium in '69.

Mike Murphy

Sorry, but that is not correct. See these two websites for proof:

http://ask.metafilter.com/21715/Diamond-hardness
http://www.didyouknow.cd/diamonds.htm

Mike Murphy

Yeah, but that 8" probably out performs some 12" and 15" "normal" subs.