Before we can make the mold, we need to create the mold positive. This is basically a case half, except we make it out of plastic. It’s not just any case half though – it’s a reproduction of our raw casting, which means that it is dimensionally different than an actual case, and it lacks some of the holes and features that a finished case would have, because those will be machined on the case post-mold.
Although scanning the case was a monumental and expensive effort, in and of itself, a Solidworks drawing of a case is pretty much useless for building the tooling needed to actually build a case.
But it’s a start.
This is where the toolmaker comes in. In order to cast new cases, you need to build tooling. Mainly, this is where the bulk of the expense lies in this little project.
Also, and super importantly, the case doesn’t pop out of the mold looking like one that’s in your car. Here are the differences:
- The raw casting needs to have machining meat on the mating halves, the mains, and just about every surface that will be machined in any way, shape or form. That means that our casting will be thicker in many places than the actual finished case, since it will be machined down later.
- We need to add draft to our drawing so that the case can be pulled from the mold properly.
- Our case is sand cast; the original Porsche® case was die cast. Die casting is a little different than sand casting, so our mold is markedly different from a die cast mold.
In short, the Solidworks drawing needs to be worked over by a team of tooling and pattern makers into something that can be used to make a mold. Which is very, very expensive!
When we decided to reproduce a Porsche® air cooled flat 6 engine case, the dilemma was which one exactly we should invest in making. It was a hard decision; there are many great cases. We were initially partial to an aluminum version of a 7R mag case, but that has its limitations. Some suggested an RSR case, with its associated head stud spacing.
In the end, we went with a 3.6 964® style case, for several reasons.
- It was latest air cooled design present, and was carried over virtually untouched to the 993® and was even the basis of the 996® twin turbo and GT2® cases.
- It has the largest spigot size available from the factory
- it seems to be the rarest and most desirable case in the aftermarket, and still remains difficult to find used.
We had a 3.6 case on hand, so we decided to use it as a basis for reproduction. Cases, however, are fairly complicated parts to reproduce; it was critical that the case be able to accept standard internals, and thus the dimensions of the case were critical.
The only real way to capture the case dimensions was to have each case half scanned, and so that’s what we did. We scanned each half to 50 microns, and then created a mesh model from that scan data which was then extrapolate into an IGES / STEP file by an engineer. From there, it was converted into a Solidworks .sldprt file, with a full feature tree.
A full feature tree allows us to use Solidworks to change any part of the case design on the fly, while having the software adjust the remaining parameters. Want bigger spigots? No problem, it’s a mouse click away.
Many will ask what the impetus of this little project was; it was actually not just one thing that made us begin the reproduction flat 6 cases, it was many things. Here they are, in no particular order:
- We grew tired of beginning expensive builds using old engine cases as a foundation. The more time passes, the more it seems that quality, rebuildable engine cases seem to be in short supply.
- The cases that are available are ludicrously priced; we get that. Supply and demand.
- No matter how nice a case you start with, you still require some degree of machining or at the very minimum, machine shop time in order to verify that the case is in spec. The mag cases are obviously the worst….you can spend $5K just to rehab one, and when you’re done, the case is really no better than it left the factory.
- For a really nice build, the cases exteriors need to be soda blasted at a minimum to remove road grime, oxidization, cosmoline, and other crap that’s accumulated for decades. Superficial? Sure, but the bottom of the car should look as nice as the top, no?
- Even if your case is perfect, you will still need to scrape sealant off the mating surfaces. We hate this. Don’t you?
So we woke up one day, and asked – why is nobody building these? No answer was heard, so in the spirit of Ferry Porsche, we decided to build our own.