[T3] T-4

[Jim Adney]

On 9 Dec 2011 at 16:55, ftalker at gmail.com wrote:

> Hi there
> > Less air means less cooling.

> This may seem to be true, but altitude also means that CR is
> contiguously lower which means, (all tuning being accurate), that the
> engine runs cooler.  

Interesting thought, but to get the same power at altitude, one would 
first open the throttle a bit more, that should bring the manifold 
pressure (vacuum) and cylinder pressure back up to the same as it was 
at sea level.

Of course once the throttle is wide open, you've got no more head 
room and you can no longer compensate, but up to that point I think 
power output should be a wash and cooling should be more difficult.

This is where turbos really shine. They never run out of head room.

I've heard that air cooled cars don't seem to suffer from cooling 
problems at altitude as much as water cooled. That info dates from 
~1960, however, before water cooled cars had pressurized cooling 
systems. I'd expect today's cars with pressurized systems to work 
much better, but I don't know if they're now better than air cooled.

I know that in 1968 I helped a family with a mid-60s microbus that 
had swallowed a #3 exhaust valve. Oddly, that happened on a long 
decent, where there should have been lots of cooling and almost no 
power output. VWs of that era seemed to bleed a bit of gas into the 
mix even on downhill overrun, so I always figured it must have been 
running lean and hot. However, I've never been very satisfied with 
that explanation.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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