On a recent road trip (before covid-19 lockdown) my 912E was having some major trouble. It was missing and bucking in the midrange. The little 2-liter was running fine at wide open throttle, and it ran fine at idle, so I figured it had to be a major vacuum leak. Since the engine was recently rebuilt with all new vacuum lines, I figured the culprit had to be the intake boot (it wasn't, but we'll get to that later). It's always had a bad intake boot, but being that Porsche only made 2099 examples of this car, the 912E-specific parts have long been impossible to find. I've tried silicone patches and extra strong tape to keep it together, but nothing seemed to work.
I didn't have much at my disposal on this road trip, and didn't have time to let silicone set up, so I bought a roll of Gorilla Tape to bodge it together until I got home. Now, before you tell me that Automobile Atlanta makes a reproduction 912E intake boot, I should tell you that I used to work there, and I've seen the poor quality rubber up close and first hand. I did not want that for my baby. Once the car was home, I set about making measurements to build my own.
Underneath all that tape, here's the old boot from 1976. It's a little gross and a little misshapen.
But the major issues are these massive cracks in the old heat cycled rubber.
As you can see, I've smeared enough clear silicone on there to plug the Titanic, but it wasn't enough to keep this boot air tight.
So, here is what I came up with. Luckily there is a Summit Racing shop not far from my house, so I placed an order for a 90 degree 2.5" aluminum elbow, a pair of silicone couplers, and a pair of stainless male 5/8ths inch hose barbs. I cut down the aluminum tube to the right length, drilled and tapped two holes for the hose barbs to fit, and cut down the silicone couplers by an inch or so. I already had the hose clamps on the shelf.
You may notice that the original boot had three fittings on it, while the one I built only has two. In this case, the case vent tube has been converted to a breather instead of recirculating back to the intake.
So, there you have it. Crafting an intake boot from scratch, and ending up with a nicer product than Porsche built in the first place. I don't believe I'll ever have problems with this again. The car runs better than it ever has, especially considering its fresh rebuild. It's nice to get a project completed, even a little one like this, in the middle of our covid-19 pandemic. I'm staying indoors and staying safe, but I can't wait to get out and drive this beast again.
[After all of that work, I found the culprit causing all of my strife was actually the ground wire in the distributor had come apart. We soldered it back on, and Bob's your uncle. Job done.]