thomasmryan

The type 1 and 3 vw motors had an aftermarket adjustable pressure release valve. The cap was threaded so you could change the spring pressure....type 4s had a tendency to blow the galley spru (freeze) plugs.

black924S

Yes I was looking at those. They also feature a shorter piston which increases bore wear. Not surprisingly, they are the exact same diameter as the 911's (15.95mm). The only VW OPRV piston that would fit in my car is the 17mm double oversize from the UK (shipping~$18 for $4 part). It is not unheard of for mechanics to re-bore the bore due to wear. Fortunately for us
however, we have a longer piston and a replaceable sleeve made out of harder material than the block.