I've only done it to the extent of relieving underhood noise and vibration... never to keep heat in.. I was always against that, actually. Being a racer, I determined that it's a bad idea to rev an engine to 9k constantly and keep all that heat in.. something will melt.
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"¿ʞɐǝɹɟ ɐ ǝɹ,noʎ uǝɥʍ 'ʇı ʇ,usı 'ʎlǝuol s,ʇı"
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