I've noticed a couple times when I get on WOT sometimes from a slow rolling start (about 10 mph,) and release throtle that I hear a hiss, almost like a loud pressure release. I know for imports they have something called a "blow-off valve" but it is not nearly as loud as that. I was just curious if anyone else has experienced this and/or they know what it is!

Thanks in advance for any input!!

 

oh yah.. it's a bone stock 2001 with about 750 miles on it, I realize it's still new and it may just be the components working themselves in, but I'm still curious as to what it may be!!

 

StrikesTwice
Hummm well im not sure what that sound could be on a bonestock 01. But i have that like hiss noise on my 00 but i got it after i put my single blade TB on. I kinda like it everytime i step on the gas a little it just sounds cool hearing the air get sucked in like that hehe. Also had a sound when i had just the airraid on that when i shut the truck off you heard air coming out of the engine.Now with the TB and 10 inch big mouth filter you really hear the air being coming out when you shut her off.
Vin

 

haha, yah, I know the sound of the air getting sucked in, but this more of a "hiss"

 

It's blower belt slip on the shift out of first.

When you let off, the trans shifts to 2nd or even 3rd and the motor slows considerably. The blower's still spinning like crazy and now the boost bypass is open, so you have no load on the blower. The inertia of the blower rotors is actually trying to drive the belt (and motor) and now the belt is being tensioned on the opposite side it normally would be. The belt tension pushes against the tensioner and the whole belt loosens up and slips on the blower pulley.

This can happen on WOT 1-2 shifts also but is less likely as the blower still has a significant load in that situation.

None of this is much of a problem from a performance standpoint, but it may speed up your belt wear.

 

Makes perfect sense, thanks Lurker!