1. The more RPM the more power.
Untrue. An engine can, and will, stop making power as soon as its ability to "breathe" (pump in more fuel and air and use it) ends, even though it is still gaining RPM and making louder exhaust noise.
2. Air-cooled VW engines cannot reliably sustain high RPM.
Untrue. The opposite true statement should be "Inadequately balanced and oiled VW air-cooled engines made from parts too weak for the stress" cannot reliably sustain high RPM.
RPM numbers get thrown around on forums a lot, and the assumption is the higher the better. But good information and apples-to-apples comparison is rare, leaving most air-cooled VW engine builders using guesswork and making decisions based off hearsay.
You may even have seen where experienced builders disagree (to put it mildly) as to what works and why. That's because builders are experts in different fields and applications, and forget (or never learned) that what works on a drag engine might not work on a road racing engine, or on any degree of street engine between the two. Not to mention that many pontificators have opinions based on theory, not experience.
As the great philosophers say, "first define your terms," so we will.
What is "high" RPM?
VW made its street engines to run at a reliable 4500 RPM before trouble started, so let's take that as a baseline. Porsche took the same basic pushrod engine design and raised it to a reliable 6000 RPM in the Super 90 with a stronger engine case, counterbalanced crank, stronger/lighter valve train parts, and better oiling.
High RPM trouble here (VW or Porsche) means the crankshaft flexing in the middle and pounding out the center main bearing, pushrods bending, valve springs breaking or going into a weird state of oscillating "float," rocker arms breaking, connecting rods stretching, con rod bolts breaking, con rods smashing through the case roof, and valve stem keepers coming loose.
Even in the 1960's the Porsche pushrod guys were lightning their valve train parts to reach 7000 RPM, much less hold it. By the 1980's, SCCA championship pushrod 356's were running 8000 RPM.
The four-cam, four-cylinder Porsche engine used in the Spyders and Carrera models was originally redlined at 8000 for the 1500cc engines and detuned to 7000 for the 2-litre engines. Power ended at about 6200 RPM, however. And the lower 7000 number was on plain bearing cranks, not the more exotic roller bearings of the small engines ... and surviving.
And these four-cam engines could do 7000 all day. But you hear pushrod guys often mention 7000 and even 8000 RPM on this forum.
A "VW type" engine (few or no original parts in it) can turn 7000 with bursts up to 8000 (for upshifts to stay in the powerband) and last a season on the road courses, which is ten to fifteen engine hours. Such an engine consists of:
Aluminum case (for strength) not aluminum-magnesium
Counterweighted crank
H-beam type rods
Lightest possible pistons and wrist pins
Straight-cut cam gear or grooved aluminum cam gear
Lightweight lifters, grooved for better oiling
Tempered aluminum pushrods
Lightest possible rocker arms
Lightest possible valve adjusting screws
Double valve springs and light alloy keepers
26mm oil pump minimum, lightest possible oil weight
Windage tray or dry sump to keep oil spray away from crankshaft
Generally speaking, the shorter the stroke and the lighter the piston (which often means smaller bore) and valve train, the more RPM you can turn, but it also means (cammed right) your power band moves higher as well. A 1600cc and a 2000cc engine might both be able to produce the same power, but the 1600cc will have to do it at 7000 where the 2000cc can do it at 6000.
And you can see the steel pushrods we use for strength with heavy duty springs or double valve springs are way too heavy. This is another plug for Aircooled.Net's tempered aluminum pushrods.
So, the answer to the question "Can a pushrod VW engine hold 7000 RPM for minutes at a time and live to tell about it?" is yes.
My father-in-law's family comes from Alesund (Valderoy) and Orsta in the western coast area.