Installed in the miserable-selling VW 411/412, the hideously underpowered (yet utterly lacking in hippie charm) 1972-79 VW Bus, and the scorned-by-Porsche-geeks 914, the Type IV engine never got quite the recognition of its Type I/II/III brethren (if nothing else, the Type I deserves recognition for being one of the only four-stroke four-bangers that will run on one cylinder). But with 1.7 to 2.0 liters of stock displacement, lots of available aftermarket goodies, (medium-difficult) swapability into hot-rod Beetles, and ready junkyard availability, the popularity of screaming Type IVs is on the upswing.
Type 4 Secrets Revealed [tunacan.net]
Related:
Brazil to End Production of Air-Cooled VWs [internal]