This is a summary of how to put a carbureted Porsche six into an aircooled Vanagon. It is presented as an aid to those who want an idea of how difficult such a project is.
The only parts you won't use are the flywheel and clutch, and the muffler. You also need an oil tank and two Porsche engine mounts. Get the tank that matches your engine. Early ones had threaded hose connectors, later ones push-on hoses, for the line from oil cooler to tank.
You need a flywheel that takes the 228mm (9-inch) VW clutch disk and pressure plate, but with a Porsche center to mate to the Porsche crank. This one is easy, since you are unlikely to do anything about it alone. Send your money to Kennedy Engineered Products. FAT Performance resells the same part at the same price if you prefer to deal with them. Since the Porsche and VW transmissions have the same pattern of mounting holes, the flywheel is the primary part needed for mating. A minor problem is that the upper mounting bolts on the VW are through-bolts that take a nut at the engine side but on the Porsche engine the bolts screw right into the case. The driver's side VW bolt is fine; it's even the right size. The passenger side bolt needs to be replaced with a socket headed bolt to clear the starter.
A slightly tougher problem is interference between the flywheel and a mounting boss of one of the case sealing bolts on the north side of the crankcase. KEP's flywheel is meatier than the stock Porsche. You can request that KEP turn yours a little narrower (the flywheels are not shelf stock -- they make them to order) and/or you can grind away a little of the bolt boss. Use a cylindrical grinding point, use a straightedge to make sure you are grinding evenly, and don't go too far. Stop often, mount the flywheel with 2 or 3 bolts, and see if it still binds.
The engine support for the Porsche engine requires that two engine mounts be firmly supported south of the engine, in a spot where the Vanagon doesn't have anywhere to hang them. Placement is fairly critical, since the position of the engine mounts will locate the engine both side to side and up and down. The third point that locates the engine/transmission combination is the front transmission mount, which is quite flexible and would allow the engine to be mounted "wrong" by many inches each way. I put a strong box-member (3-inch width, 1/4 inch wall, aluminum) across from one frame rail to the other, and mounted the engine mounts to it. The box member needs a long mail slot cut in the bottom to clear the Porsche engine brace. Big U-bolts hold the bar in place on the frame rails once you have it located perfectly. This is the only "no-welding" solution I could figure out. Note that the engine/transmission combination is in line with the car but offset over a half-inch to the passenger side, so don't try to get the two sides even.
The Porsche six is a dry-sump engine; oil is stored not in the crankcase but in a separate tank. The quantity of oil is not 3-4 quarts like the Vanagon 4, but 10-12 quarts. The good news is that there is a natural space for the oil tank next to the engine, very close to where it is located in a Porsche. The bad news is that quite a large hole needs to be cut for the tank, in the metal that makes up the south wall of the wheelwell and the floor of the engine compartment, below where the FI box hangs. This area gets spray from the passenger side rear wheel, so it is not an area where you want your engine to be getting air. Cut as close to the oil tank dimensions as you can, and seal open areas with weatherseal when the tank is in. I made a cardboard model of the area, and trimmed till it fit the tank perfectly, then tore the model apart and used it as a template.
The stock VW accelerator cable is roughly correct for length, but it reaches the engine on the wrong side of the car: The Porsche engine expects the accelerator about 10 inches west of the centerline, rather than east. To allow it to slant across the bottom of the car, and up past the clutch cylinder, holes of 1/2inch or more diameter must be drilled in the front and back walls of the cross-member that the transmission front mount attaches to. Be sure not to nick the brake line in the course of drilling either hole. Once the cable reaches the west side of the engine, thread it through the north engine sheet metal, and cobble it to the carburetor linkage. I stole the appropriate part from an old VW fuel injection and bolted it to the carburetor linkage. A less neat but still effective hookup could be made by clamping the cable to the carb linkage with hose clamps. While you're in the area, get some WD40 or other lubricant, maybe with some graphite, down the cable so it runs smoothly, since it now has two new curves in it.
VW flapper valves are a tolerable, not perfect, fit on the Porsche heat exchangers, and are located such that the stock heater cables still work unless you break them getting the VW engine out.
Nothing tricky. Wire from Porsche alternator to VW starter and red-dash-light wire. I am using stock Porsche distributor, stock VW coil, and cheap J.C. Whitney capacitive discharge ignition.
Buy aftermarket oil pressure and oil temperature gauges, making sure that they are correct for the Porsche senders. Put the oil pressure sender on a tee so you can retain the VW oil pressure light sender. You may want to get an oil level gauge and connect it to the sender, but I've never had an oil level sender that worked, so I ignored it. Check your oil with the dipstick. Buy an aftermarket tach that works with your ignition. There is nowhere on the VW dash to put the gauges so they look good. Put them where they fit. Rich people put in a complete Porsche dash cluster, but I wouldn't know about that.
Probably you could get away with teeing together the vacuum from the bases of two carbs. I have a fabricated vacuum box with ports for seven hoses, so I take vacuum equally from all six carbs.
Shrouding The air above and below your air-cooled engine (VW or Porsche) should not mix. The air below is warmed by the exhaust and by passing through the engine. The air below also has road dirt and exhaust gases in it. The air above the engine is what cools the engine, and what the engine takes into its carburetors. The air above the engine is also what you breathe when the heat is on. Again using cardboard templates, design additions to the Porsche sheet metal, to reach within 3/4 inch of the walls of the engine compartment. Then the stock VW airseal will work fine. Tricky parts are at NW and NE corners, where the trim has to turn a horizontal and a vertical corner in one smooth curve. Look at the stock VW tin for ideas.
The stock Porsche muffler won't fit. It interferes with the southernmost chassis crossmember. A Sebring muffler from Performance Products will fit, but is very loud. I'm using the headers from the Sebring, and a medium-sized muffler that slants northwest from behind the engine. Still a little too loud, but it's all I can fit in the space. [Note added in 2003: The stock Porsche muffler WILL fit, but only if the engine hangs several inches lower than stock.]
Replace the high-pressure FI fuel pump with a 2-4 psi Facet pump appropriate to the carburetors. Drill one new hole so you can use the same rubber mountings as the stock pump, or the noise will drive you crazy.
The MSDS kit recommends that you use the 3.2 and later engine, which with some minor trimming will fit under the stock engine lid. Less expensive Porsche sixes have taller induction systems (2.4 to 3.0 liter CIS FI systems are tallest of all). Luckily the area where extra height is needed is within the area defined by the removeable decklid, so you'll just need to make your decklid taller by six or eight inches, without affecting how the decklid seals to the luggage floor around its perimeter. This can be done with sheetmetal and pop-rivets, or by welding a box on top. Either way, for good sound and smell insulation the box should seal real well. If you want to be able to get back to stock, get another decklid from a wreck and save your original lid.
You have to decide whether it's worth it. I'd do it again in a minute, and was pleasantly surprised that I and my ill-equipped garage were up to it. I was prepared for the possibility that I would have to put the VW engine back in and punt. But the problems are all solvable and the big cost is right up front where you can see it: a Porsche engine that in my case is worth as much as the Vanagon itself. Good luck to all those who take on this type of project.
B.