Intake Manifold Temperature 1

[SBBlue]

Here's a little bit of a strange question.

What is the typical temperature in the intake manifold for a naturally aspirated spark ignition engine?

Here's why I was wondering. . . .

The intake manifold is, of course, below atmospheric pressure for a NA engine except for full throttle conditions. Since the engine has to perform work on the air to get it below atmospheric pressure, the temperature of the air will drop.

According to my calculations, dropping the pressure of a container of air from one atmosphere of pressure to one-fourth atmosphere will drop the temperature from 80 deg F (assumed ambient) to something like 80 degrees below zero.

This phenomena does, of course, account for icing that is frequently encountered with piston airplane engines.

The intake manifold air will be heated by the surrounding engine, but to how great an extent?

Since I started thinking about this I haven't had a chance to put a temperature probe in an intake manifold.

Has anybody ever done that?

 

[SBBlue]

Thanks, Larry.

It looks to me that there is minimal temperature drop across the throttle. I suspect the slight increase in temperature seen at idle is secondary to heat from the manifold being transferred to the air in the manifold.

The temperature drop at high loads might be explained by the Joules-Thompson effect. I seem to recall some calculations I did several weeks ago suggested that there would be about a 10 deg F drop from that effect.

 

[MaxRaceSoftware]

with a Holley carb and Edelbrock intake on this engine

Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
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