Just swapped out my older Bosch W7DC0 pluggies for new NGK BP6ET.

Either tencentlife (Chris Corkin) is right: "The main reason this plug
design so often produces palpable improvement in idle, throttle
response, and overall performance is mostly due to the projected core,
and that is helped by the side electrodes not "shading" the spark gap
from the middle of the charge. The wbx has a very compact, somewhat
"spherical" charge at TDC, as well as outstanding squish dynamics, so
initiating flame nearer to the charge center aided by the squish
produces a faster total burn, and fast burn is the principal requirement
for responsiveness, efficient use of the fuel, and lowered emissions
(especially NOx)."

<http://www.thesamba.com/vw/forum/viewtopic.php?t=327351&start=80&sid=2b4a44c5892001fb15120a77e2dd8767>

or it's the New-Spark-Plugcebo Effect.

But I definitely feel that the throttle is more responsive and the van
peppier.

No increase in real power, of course: took the van up my neighborhood
calibrated steep street and it didn't climb any faster. But I'm pleased
anyway.

--
Jack "Rocket j Squirrel" Elliott
1984 Westfalia, auto trans,
Bend, Ore.