At 04:10 PM 11/27/2004, you wrote:
>But, in a "stock unmodified" engine (no head work,no exhaust work, stock
>cam, stock displacement) will opening up anything upstream of the head make
>any tangible difference?
>I'm still thinking no, provisionally.

"No" assumes that the entire intake system is adequate for the waterboxer's
capacity and there is no significant intake restriction.

>Remove the rubber connector between the AFM and the air filter box and drive
>around the block.  There will be more noise, but more power?

If the AFM is a major contributor to the problem, as Jim suggests, no, just
pulling the filter box off won't make any difference. In fact, just pulling
those off can even make it WORSE. Part of the job the filter box/snorkel
plumbing does is provide nice, non-turbulent air flow into the system. I've
never pulled the airbox off my waterboxer, but I tried it once on my Datsun
280Z and it created so much turbulence in the system at a certain RPM that
my air flow meter started "flapping" and nearly stalled the engine.

>However, simply giving your unmodified engine *access* to more air will not
>give you more hp

Unless the intake tract can't feed the engine as fast as it can suck! Jim
indicated a 1 PSI drop at high RPM with the stock system. Ideally (on a
regularly aspirated system), you want your combustion chamber to fill with
an air-fuel mixture at the same pressure as nominal air pressure. The
problem is that the air is resistant to being sucked into the system. The
best way to minimize resistance is to have a HUGE STRAIGHT PIPE all the way
from filter to intake valve, but the limitations of space and geometry make
that pretty much impossible. Subsequently, compromises are made: the intake
is bent at 90 degree angles three or four times, the piping is made small
enough to fit through existing bulkhead spaces, the air flow meter is made
to fit the space between the hood a radiator hose, etc. My old  280Z had a
plenty big intake system from the valves to the throttle body, where (for
various reasons related to CA smog requirements and also smooth,
"civilized" engine response) it pinched down some 15% in size. Replacing it
with a 60mm unit added a significant boost to the mid and high end numbers
(and DEFINITELY made it less "civilized"). Basically, you can't just assume
that the engineers who built the system spared no expense and considered
nothing else but airflow when they designed the intake system, because
that's seldom the case. There are very, very few cars where there isn't
room for improvement. Looking at the various engineering shortcomings of
the rest of the Vanagon powerplant/drivetrain, do you REALLY think that
intake system somehow bucks the trend and offers ideal airflow?

John Bange
'90 Vanagon "Geldsauger"