I've had a couple of responses to my question.  Most saying that 
there shouldn't be a problem cause as the engine turns faster more 
air flows to cool the engine, or that I have a leaky engine 
compartment.  '80 Westi.  Engine compartment has no holes bigger than 
a quarter.

Well here's what I know.  During my downhill travels I freewheel and 
use my brakes (CV's are shot and I reversed them so make ugly noises 
downshifting, so I don't).  When I do that the engine oil temp drops 
about 30 degrees.  As I sit in traffic and idle the oil temp rises.  
According to the above logic, if I sit in traffic and rev the engine 
my oil temp should drop!  I'm not willing to try it.  So my theory 
still applies, revving my engine up while on a dyno would overheat my 
engine as insufficient air is being scooped into the engine 
compartment.  Vehicle speed = better cooling. That's why later busses 
had outdented intakes, ie scoops.

Some of this must be the case, as they put a fun in front of those 
watercooled standard cars to increase the air flow.  Where would they 
put one for a VW?

If the dyno testing is short, it may not affect anything.  One 
response to having had it done to a Type3.

- Jeff '80 Westi, '67 Sqbk