<VV> valve seats (Now Engine bay Temp)

[Ken Pepke]

Doc:
While I am with you on many of your points I would like to point out that the only incentive outside ambient temperature air has to enter the LM engine bay is offered by the fan forcing hot air out of the bottom of the engine and thereby creating a lower pressure area between the deck lid and the fan inlet.  This is unlike a conventional vehicle with a grill and radiator that sees high volumes of air movement by virtue of the vehicle's forward motion.  There is surprisingly little air motion along the sides and across the tail panel on the inside of a Corvair engine bay but there is a great deal of radiant heat back there and that is the point of induction air pickup.  

As I said right up front ... It is not an exact science.  Of course, almost anyone could jump out of their Corvair after a long run and touch the outside of the tail panel.  You can bet that if it is hot on the outside it will be hot on the inside.

Ken P
Wyandotte, MI
Worry looks around; Sorry looks back, Faith looks up.

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On May 11, 2012, at 3:01 PM, RoboMan91324 at aol.com wrote:

> Hi Ken,
>  
> I am one of those people who believe the engine bay remains relatively close to ambient.  Of course, this is with qualifications.  I haven't taken measurements so, keep in mind that this is theory but still probable.  What you may be thinking of is what happens in the engine bay of a water pumper.  In that case, the engine is stuck in the middle of the bay radiating heat.  Further, the engine bay is downstream from the engine coolant radiator and in most cases the radiators for the trans cooler, A/C, etc.  The ambient air in the Corvair's bay is truly outside air and the engine is downstream from the bay.  In the water pumper, the engine is in the bay and there is a huge temp rise from the radiators.
>  
> However, yes, there will be some temperature rise in the Corvair bay but I suspect it will be different at different parts of the bay, at different engine RPM and different engine loads.
>  
> 1. In different parts of the bay-  In the air path directly from the air inlets from outside the bay through to the fan, I would think the temperature rise should only be a few degrees max but it depends on the turbulence in the bay.  I imagine the worst case location would be in the little pocket down by the crank pulley/damper because there are several heat sources there and minimal air flow.  I would think air temp to the fan is the most important factor in this discussion as cooling of the engine is most important.  Air temp to the carbs is also a factor which is why I would shy away from the individual short stack intake systems.  Pulling air in from the upper part of the bay would probably result in cooler air to the intake.  Pulling air in from the sides of the bay and from closer to the heads might result in higher intake temperatures.
>  
> 2. Engine RPM- This is a major factor in that it determines the volume per unit time of air flow through the bay.  In effect, the amount of air entering and exiting the bay goes way up as RPM increases and there is less time for it to pick up heat as well as much more volume to absorb (spread) the heat energy.  Of course, this flow rate depends on whether the air is allowed to exhaust out the back.  This complicates things significantly.
>  
> 3. Engine load-  Obviously, the engine generates more heat as the engine load goes up.  The worst case scenario would be if you are going relatively slowly with a significant load such as going up a steep incline.  You will have significant heat generation in the engine which will increase radiation, conductive and forced convective heat transfer.  At the same time, the RPM will be low which results in less volume per unit time of air through the bay and engine.  It is a double catch in that the engine is generating more heat which somewhat raises the temp of the cooling air at the same time as it is suffering from diminished air flow when it needs both higher volume and cooler air.  It is no wonder this seems to be the situation that leads to the most dropped valves both during the event as well as after many such cycles.
>  
> I would like to see some data if someone would like to perform the experiment.  I don't have the equipment.  I think the most important points of measurement would be ambient temperature at the point of entry into the bay and at the point of entry into the fan.  Secondary locations would be ambient vs. the carb intake both with and without the air cleaner/ducting in place as well as other locations like near the crank pulley/damper.  If possible, data should be taken at idle, at high RPM under high load, at high RPM at low load, at low RPM under high load and at low RPM with low load.  The data must be recorded while each of these situations is taking place.  If you pull over to take the measurements, the data is completely useless.  The air flow changes immediately, the air exhaust flaps close almost immediately, etc.  This test would require either a multi channel recording device or a multi channel recording human.  It might be dangerous for the driver to drive at the same time as taking measurements.  The ambient temp must be recorded at the same time as the other measuring points because the ambient temp will change as you drive around.  If this is not done, the data is useless because if the ambient temp changes from location to location, how can we measure the differential if we take only one ambient temp measurement at the start of the trip?
>  
> A factor that would complicate things is the air exhaust flaps.  Perhaps a car with the air exhaust ducting and flaps removed would be the best test vehicle so this variable is eliminated.
>  
> Doc
> 1960 Corvette, 1961 Rampside, 1962 Rampside, 1964 Spyder coupe, 1965 Greenbrier, 1966 Canadian Corsa turbo coupe, 1967 Nova SS, 1968 Camaro ragtop
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In a message dated 5/11/2012 6:42:09 A.M. Pacific Daylight Time, virtualvairs-request at corvair.org writes:
> Message: 4
> Date: Fri, 11 May 2012 08:24:41 -0400
> From: Ken Pepke <kenpepke at juno.com>
> Subject: Re: <VV> Fwd:  valve seats
> To: "Ron" <ronh at owt.com>
> Cc: Vair Views <virtualvairs at corvair.org>
> Message-ID: <595D41B9-6D0A-4AA8-9922-254FFA27DFD8 at juno.com>
> Content-Type: text/plain; charset=us-ascii
> 
> 
> There are those on this list that believe the Corvair engine bay remains about ambient temperature and that all that hot sheet metal radiates little or no heat into the bay.  You must be among that group.  I am not. 
> 
> Ken P
> Wyandotte, MI
> Worry looks around; Sorry looks back, Faith looks up.