Look where your filter sits. I'ts right behind the cooling fan for the radiator. Sucking hot air right out and directly into your filter. The stock setup is enclosed and only pulls cold air from the front "Hence cold-air box". You might still have that little piece of ducting going to your filter but it's just mixing with the other air and not staying "cold". Try and make a heat sheild to block the air from the fan and it might help a little.