Correction to my earlier message:

Of course the more efficient combustion makes it possible to REDUCE the
ignition timing setting if preferred and this gives more safety margin.

Sorry about this lapse

JP


"JP" wrote in
...
Such liquid cooled cylinder heads offer some noteworthy benefits. I am not
still saying that they are perfect or that this is an optimum VW engine
solutions.

These liquid cooled heads are equipped with dual sparkplugs. That means,
the combustion process is initiated more rapidly and evenly. The engine in
question does have two separate electronic ignition systems. They are
superior to any conventional magneto ignition systems and much better than
a point ignition system. That is why the ignition spark is more powerful
and the matter comes back to the more rapid ignition process activation. I
would imagine the combustion pressure build-up to be smoother and the
combustion pressure to be higher. If so, then the smoother combustion may
produce less than average shock loads to the cylinder studs and to the
cylinder block and rotating parts in general. The combustion inside the
cylinder is more complete and that is why the exhaust gas temperatures
most probably are lower than usually seen, because less burning is taking
place while the exhaust gas is moving to the exhaust system. That is why
the heat load to the cylinder head exhaust ports is reduced (less head
distortion load).

The liquid cooled cylinder head runs cooler compared to an air cooled
version. That is why the head is capable to absorb more efficiently heat
flow from the exhaust valves and the valve temperatures are reduced. This
is the major reason, why higher compression ratios can be used. That is
also the reason, why more power can be taken out of the engine compared to
the air (oil) cooled standard version. The liquid cooled head also absorbs
more efficiently heat from the spark plugs, thus reducing (together with
those reduced exhaust valve temperatures) a risk of pre-ignition under
high power settings. The risk of detonation is reduced thanks to the dual
spark plugs. This gives a possibility to increase ignition timing in order
to get more power reliably. A cooler cylinder head may even act as a heat
sink taking heat energy out of a cylinder barrel top part.

Possibly there's even more explanations but these are the ideas surfacing
right now.

JP

"Jim Carriere" wrote in
et...
wrote:

I think the major reasons for the improved output are
1) the liquid cooling allows a higher compression ratio
2) improved heat dissipation over the well known cooling fin limitation
on VW heads