Quote:
Originally Posted by ratgreen
In regards to the OP. What temperature does polyurethane degrade? I've read that its 107'C. Would the mating surfaces of the intake manifold stay below that?
I love this idea, almost purchased a sheet of phenolic sheet to make my own spacer by hand but PU mold would be way easier.
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Quote:
Originally Posted by Daox
The material I use holds up to 244F / 118C. Since the engine coolant runs at a max of around 200F / 93C, and the intake manifold is essentially a big heat sink, I would be incredibly surprised if the head got too much warmer than that.
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If the spacer were aluminum, the manifold would indeed continue to be a heat sink for the head. However, an aluminum manifold with a plastic spacer will effectively cease to be a heat sink for the head. At that point, if your fuel delivery system is wet-flow (carburetor or TBI), the manifold will see significant cooling due to the latent heat of vaporization of the fuel, which can cause mixture separation and
worse performance.
Note that post-shutoff engine temperatures can spike significantly once the coolant and air flow have ceased. On one of my vehicles, I used four thermocouples to test the efficacy of a carburetor spacer and/or post-shutoff fan operation, and observed a 20°F spike when there was no post-shutoff air flow. For the thermocouple taped to the outside of the stainless steel thermostat housing (with heat-transfer goo interfacing the thermocouple & metal), the result was this:
Note that this data was gathered to show
trends, not absolute values. The sampling interval for the no-fan condition was 5 minutes, so the spike shown was
at least 20°F; the sampling interval for the fan-on condition was 1 minute. Since stainless steel is not tops for heat conduction and the thermocouple was on the outside of the thermostat housing, the actual coolant temperatures were probably 10°F+ higher, especially when one notes that the fan switch shutoff temperature rating is 165°F and the data shows the shutoff at ~150°F.
(Sorry for the thread derail!)