<VV> valve seats

[Dave Keillor]

Sorry for the delayed response, but I've been busy trying to get the car
back together.  Two points:  First, I'm using a VDO thermocouple gauge, not
the stock thermistor.  A thermocouple measures the difference in
temperature between the hot junction and the cold junction.  With the VDO
gauge, the cold junction is about a foot from the hot junction.  Therefore,
as the temperature where the cold junction is located rises, the
temperature indicated on the gauge falls.  Second, I suspect that the
temperature rise is about the same irrespective of the outside ambient --
at least with any reasonable ambient.

Dave

On Fri, May 11, 2012 at 2:39 PM, <RoboMan91324 at aol.com> wrote:

> **
> Hi Dave,
>
>  I think what you are asking about here is different from the question
> posed about the temperature rise from ambient to that in the engine bay.  I
> contend that the differential between the ambient and bay temps is
> minimal.  What you are interested in is the bay temp in and of itself.
> Depending on where you live, this can be very significant.  In Minnesota,
> the coldest real temperature I experienced was minus 60 degrees and the
> highest was around 100 degrees.  This does not include wind chill or
> humidity factors.  160 degrees swing in ambient/bay temp would definitely
> have an effect on your engine temperature and thus, your CHT.  However, if
> I understand your post correctly, you are probably wondering if changes
> in the bay air temp will effect the accuracy of the CHT reading .
>
> I think the impact of the bay temps will be minimal on your CHT.  My
> assumption here is that you are talking about the direct interface of the
> air with your CHT.  Your CHT will be attached directly to the head either
> through a "washer" clamped between the spark plug and the head or attached
> somewhere else to the head like the sensors on our Spyders and Corsas.  In
> either case, the measuring device will be somewhat isolated from air flow
> in that the thermistor will be in close contact with the head and not
> sticking up into the airstream.  A huge variation in the bay's air temp
> like 160 degrees would have an effect on the head's temperature but the CHT
> would still accurately measure the head temperature at the point of
> measurement.  The only thing that might change would be in the system that
> clamps between the spark plug and the head because the plug sticks up into
> the airstream and could possibly act like a cooling fin/pin.  I do not know
> how you might measure this effect but I suspect that it would be minimal
> considering that the upper portion of the plug is covered by a rubber boot
> which insulates it and the small amount of ceramic of the plug which lies
> between the head and the boot does not conduct heat well.
>
> With that said, my statement is theory and you should feel free to conduct
> your test.  While you are at it, perhaps you can test the bay vs. ambient
> issue while you are at it.  This assumes that you can sample two locations
> at the same time.
>
> Doc
>  1960 Corvette, 1961 Rampside, 1962 Rampside, 1964 Spyder coupe, 1965
> Greenbrier, 1966 Canadian Corsa turbo coupe, 1967 Nova SS, 1968 Camaro
> ragtop
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>