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I installed a NAPA 6637 air filter in my 2000 SD 7.3 Auto this weekend and it seems to improve throttle response. My questions for you guys are: what is this noise I am hearing under harder load that sounds like the noise you make when you tighten your lips and make that squeeking noise, and the noise after it shifts that sounds like you let the air out of a tire very quickly? I know what my turbo sounds like and I don't think this is it, although I can hear my turbo more now. It sounds like some type of sucking sound under load and like there is a blow-off valve after it shifts when the turbo slows down. Please help, I dont want to damage my truck. Thanks
The "blowing" sound is normal for the large "open type" air filter. Friends that ride with me think it sounds cool. This sound has always been there, but muffled by the air cleaner box. The "squeaking" sound is not common to my truck. I would check all your hose connections for looseness.
The sound is fun! When you accelerate with a load, boost builds. When you shift, that level of boost cannot be maintained by the lower RPM of the engine (and lower compressor speed), and the engine isn't turning fast enough to take in the pressure you just built up. So, the excess pressure has to go somewhere.
It eseentially bleeds back through the spinning compressor and gives that sound. The pressure leaking back through the intake system is also the reason why oil (from the CCV) ends up making the stock air filter a bit oily after a while.