I don't think there is any significant increase in compression ratio.
Someone would have to cc the combustion champers carefully with each
type of plug and compare.
My hunch is the CR factor is zilch.

Emisisons could be a consideration the designers had in mind for all we
know.
I doubt this ..but say one spark plug type cost VW 25 cents less than
the other ..
times hundreds of thousands of spark plugs in production ..that adds up.
Though I doubt this is really a factor.

I am strongly against premium fuel in stock vanagons.
If you want more octane use mid-grade.
if it doesn't ping, you're ok.

On 8/21/2012 6:56 PM, Rocket J Squirrel wrote:
> Then if the Vanagon's 1.9 engine was contemporaneous with the in-line
> 4/Audi 5 engines (I'm not familiar with the timelines of various flavors
> of engines that VW used), it suggests that the engineers had access to
> "D" length plugs and said, "Nein!".
>
> Could one compensate for the increased risk of ping by using
> higher-octane fuel?
>
> --
> Jack "Rocket j Squirrel" Elliott
> 1984 Westfalia, auto trans,
> Bend, Ore.
>
> On 08/21/2012 06:45 PM, Dennis Haynes wrote:
>> Yes, all the in line 4/Audi 5 engines used the "D" reach plugs.
>>
>