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Old 08-22-2006, 06:27 PM   #6
Scooby Newbie
Member#: 72132
Join Date: Oct 2004
Chapter/Region: NWIC
Location: Spokane, WA
2000 Legacy GT


Although the actual air temperature under the hood may stay within the same range as the outside air temp you need to worry more about radiant heat from the engine. The best way to do that is to have a reflective surface on the outside of your intake or build a heat shield between the intake tube and the engine.

It does make much of a difference in any case.... I had an engineer calculate the heat gain of the air passing through a 3" aluminum tube that is 24" long @ 150 cfm (a 2.5l engine at 6500 rpm intakes 250 cfm). If the engine compartment is 110 degrees F and the air traveling into the intake is 96 degrees F. He calculated that nearly all the heat would penetrate the intake tube. Meaning that the intake tube is still going to be atleast 110. With all of these parameters the entering air temp would be 96 degrees F and the exiting air temp would be around 98 degrees F. Not a big difference.... this doesnt take into account however the increase in temp of the intake tube caused by radiant heat from the engine, so you could expect the intake tube to get hotter than 110 degrees. he said that even wrapping the intake tube with R-3 duct wrap wouldnt do much.

One thing I thought of after talking to him was to make a heat shield to place between the intake and the engine to help block the radiant heat......
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