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Using Magnesium Engine Parts

At what stage of tune would it be adviseable not to use the following magnesium parts on an engine build

engine maincase

upper cam cover

lower cam cover

timing chain housing

I am also not sure what fit issues there would be eg stud pitch, suitable crank shaft if I was building a 3.3ltr or 3.6ltr capacity engine.

The reason I ask is it would be nice to offset some of the extra weight of a turbo installation with the reduced weight of the magnesium parts

Are there any other magnesium parts I should consider and what parts do people on here run, if any?
Old 02-09-2010, 01:10 PM
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Wouldn't head studs pulling out be an issue? Or would timeserts fix that permanently? I imagine the case would need to be shuffle pinned even at std HP numbers.

Someone correct me if I'm wrong, but I think an aluminum case is a better starting point.

If you don't have emissions issues, getting rid if all that, an aftermarket exhaust/muffler, a/c parts, etc. would lighten the engine greatly. After that, I'd look at what I could do to the car.

Last edited by A930Rocket; 02-09-2010 at 02:33 PM..
Old 02-09-2010, 02:30 PM
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I think that the timecerts would cure the studs pulling out. The problem with the alloy that the Porsche case used is the basic strength (Tensile Strength) and deformation under load at high temperature (creep). I don't think it would hold up very long as a turbo motor.

A magnesium turbo motor would be interesting, one third lighter than aluminum. There are even alloys available now that could probably pull it off. Google Magnesium-Elektron.
Old 02-09-2010, 08:38 PM
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If you are talking about using a mag case from a 74-77 911 the max bore is about 93mm and I doubt you would run a turbo on it as that is getting thin. Unless you could find a away to mod the case for a later crank this puts your limit at 2.9.

There is a guy here that built a 2.8tt making 450hp but that is crazy stuff.

Maybe look to other areas for weight savings or just make more HP.

Tial makes a stainless turbine housing that is much lighter. Keep the exhaust plumbing short and w/o heat.

Some wast gates are lighter than the Porsche units.

You could use a 92-95 plastic intake.

A wasted spark system might save some of the weight of the distributor.

The on motor oil cooler can be replaced with a block off plate if the front cooler is sufficient. Porsche did this with the 91 turbo but put an oil filter there.

Most the extra weight is going to be in the intercooler. You could look into a tube and fin intercooler over a normal bar & plate but the B&P seems to make for more performance with a smaller core.

Could go with a low pressure system with say .5 bar boost and 8.5/1 compression and run without any intercooler. This might let you find a turbo with a built in wast gate.

Could consider water or alcohol injection for intercooling.

However, many of the vintage racers dump the mag cases for aluminum for the increase in reliability.

Just a few thoughts.
Old 02-10-2010, 07:06 AM
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As with many things you need to establish goals. Most of the guys on this board want fire breathing turbo motors for their 930 cars, however with restraint there are custom built turbo motor options for installation in lesser Porsche 911 based cars. Choosing this route you can also build a much lighter overall drivetrain.

As mentioned earlier the magnesium case has its limitations. Some speak to HP and others heat but they are one in the same. To produce a fixed level of HP you will produce and need to reject a fixed level of heat. Heat is the enemy of all motors but an especially troublesome and limiting factor for air-cooled motors.

If you do not track your car you should be capable of producing 250-275HP turbocharged and retain the weight savings of the magnesium case. A 2.4L based motor with 7R crankcase, E cams, T pistons (7.5:1) with existing modified CIS should do it. Turbos are generally light, wastegates not so, but this can be done with a much lighter package of small K16 with integral wastegate. l would avoid the temptation to bore this crankcase for larger cylinders, stay at 2.4L.

If you are driven to extreme weight reduction you could use the non-counterweighted 66MM T model crankshaft and a 2.2L motor, however you would need to drop compression to 7:1 and bump the boost to high level make up for the reduced displacement and RPM limitation this crank represents.

The added benefit of this small motor/ limited HP approach is you control torque and retain the lighter 915 magnesium case. Just build it with short or long gearing. All this assumes you also desire an austere car weighing <2200#.

Other considerations-
Valve covers: AL are more robust and will remain flat longer. If those two considerations are subordinate to reducing weight, mill your four magnesium covers flat and use them. When or if they distort and leak do it again.
Timing chain housing/covers, use them.

Last edited by copbait73; 02-10-2010 at 08:39 AM..
Old 02-10-2010, 08:13 AM
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My personal belief is that magnesium shouldn't be used on anything structural except on a race car. Covers would be fine. The stuff just corrodes so bad you don't know what condition it's in til it fails.

If you're trying to shave a few pounds, I'd get rid of the turbo.
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Old 02-10-2010, 08:41 AM
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The factory 2.1 RSR engine was all mag. My 2.3L turbo project is all mag, too, and uses a 2.4L 7R mag case for strength, plus shuffle pins and case savers. I would not exceed the smaller bore for a turbo on a mag case. My research leads me to have no concerns on this motor which will make well above 300 RWHP at 8.5:1 CR, around 1.5 BAR...static CR w/ cams makes it peachy. And yes, I am using sequential EFI, twin plugs, ITBs, knock control and methanol inejction with a water/air IC to get there.
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Last edited by kenikh; 02-10-2010 at 12:18 PM..
Old 02-10-2010, 12:13 PM
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It could be done, but I would think there would be risk involved. Magnesium is not the most stable metal. I swore off magnesium cases after one cracked on me. That case was shuffle pinned, has Timeserts, and all the other mods. I went with aluminum after that and haven't looked back. My .02, I would think you can find the 15 or so pounds in other, less risky ways.

Scott
Old 02-10-2010, 01:56 PM
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Quote:
Originally Posted by stownsen914 View Post
It could be done, but I would think there would be risk involved. Magnesium is not the most stable metal. I swore off magnesium cases after one cracked on me. That case was shuffle pinned, has Timeserts, and all the other mods. I went with aluminum after that and haven't looked back. My .02, I would think you can find the 15 or so pounds in other, less risky ways.

Scott
I am curious what the stroke and bore was, how much power it was putting out and what the top RPM was.

My research tends to reflect that the vast majority of cracking in mag cases happens at the reinforcing webs and at the spigot bores. The most common direct correlations between failure are:

70.4mm and longer cranks
92mm and larger pistons
Peak RPM of 8000 and higher

Each of these also seem to exacerbate the other.
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Old 02-11-2010, 06:13 AM
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The engine I currently run is and oversquare 2.7L (93mm x 66mm). I shift at 7500, and the engine has never seen over 8000. The engine makes about 260 hp (this is an estimate). I would have thought a well-prepared mag case would have handled this, but my experience was different. My scenario is probably a rare one. But I think it's fair to say that aluminum is significantly stronger than magnesium, and I guess I just prefer to err on the side of reliability when it comes to a race motor's crankcase.

Scott
Old 02-11-2010, 07:31 AM
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Quote:
Originally Posted by stownsen914 View Post
The engine I currently run is and oversquare 2.7L (93mm x 66mm). I shift at 7500, and the engine has never seen over 8000. The engine makes about 260 hp (this is an estimate). I would have thought a well-prepared mag case would have handled this, but my experience was different. My scenario is probably a rare one. But I think it's fair to say that aluminum is significantly stronger than magnesium, and I guess I just prefer to err on the side of reliability when it comes to a race motor's crankcase.

Scott
First you are right...Aluminum is much stronger. This is why Porsche chose aluminum to support 700HP turbo motors. They have lots of runway, where mag doesn't.

Your spec is definitely "at (or over) the limit" for any mag case, even a well prepped 7R. The short stroke crank was defintely to the motors benefit, but 93mm is in the "danger" category for P/Cs on mag cases due to the thinness of the spigot bore. 7500 RPM, while below 8K, is still pretty high, given this. Was the crank counterweighted? If not, the rocking stress from an non CW crank is also contributory.

A well prepped mag case is only one factor for a motor of this spec. Anyone running 93mm pistons should spend an inoridnate amount of time lightening the rotational mass of the internals and balancing the components to ensure that rocking stresses are mitigate as much as possible. R&R rods, JE FSR pistons all help here. Nickie cylinders help too, since they require thinner skirts than Mahle, so you can keep more meat on the spigots, too.

Steve Weiner and I have talked A LOT about the challenges of mag cases. He feels that specced correctly, they can live a long, long life without cracking. He said that it is when you push any of the above items, you can run into problems.

Net-net: keep the bore small, the case well oiled and reinforced, the rotating compenents as well balanced as possible and the stroke short, if possible and 300HP is well within these cases' ability to manage reliably.
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Old 02-11-2010, 07:54 AM
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In the earliest days of selling turbocharging it was accepted that an engine can make similar power IF reved high. However, the cost goes up exponentially and reliability down in like fashion because the forces of high reving are much higher than those of supercharging(turbos include). This is the beauty of supercharging.

Kenik has a program to do both. With that he will make high power but also have the risks and cost. My scenario does not include pushing the RPMs past stock limits or include overboring the motor for its marginal HP contribution, therefore the HP gains will be less. They will however allow use of Porsche components that are readily available and make for a high power density lighter weight engine and trans combination.
Old 02-11-2010, 07:55 AM
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Building motors is a complex dance with compromise.
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Old 02-11-2010, 08:07 AM
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Quote:
Originally Posted by kenikh View Post
Building motors is a complex dance with compromise.
Well said, and I admire your drive and financial commitment to building a "small block" Porsche Turbo motor.
Old 02-11-2010, 12:23 PM
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Well said, and I admire your drive and financial commitment to building a "small block" Porsche Turbo motor.
TELL ME ABOUT IT.
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Old 02-11-2010, 12:28 PM
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Thanks for the replies, the answers have been very helpful.

At the moment I have a very clear vision of how I want to build the chassis but am undecided on which way to go with the engine and transmission.

The chassis would be a tubular steel space frame similar in concept to a 908 or 917, ie mid-mounted engine, independent suspension, cast aluminium uprights, knock-off wheels, biased brakes etc. The race inspired mechanical parts would be covered by a discrete stock looking pre-73 or later impact bumpered narrow bodied coupe shell using a lot of lightweight composite panels.

For the pre-73 shape I am thinking of a lightweight small capacity max 2.8ltr NA engine hence my magnesium questions. Or for the impact bumpered shape using a heavier twin turbo'd 400bhp engine with a G50 trans. I don't want to go extreme with the power levels as I don't think I will need it as I am aiming for an ambitious total car weight of 1800lbs.

The easy option would be to use a later 3.6 NA engine but I would like the overall look of the car to be period correct at the time of manufacture for which ever body shell I end up using. As if Porsche had built a road car from a homologated silhouette race car.
Old 02-11-2010, 12:36 PM
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Build an RSR spec 2.8 short-stroke on an early turbo aluminum case. None better for your purposes.
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Old 02-11-2010, 12:39 PM
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