super chevy

Truck idles and runs great. No vac leaks anywhere.
It's just that there is a noticeable hissing/whistling noise from my air cleaner right after you tip the throttle and last for a few seconds.
I've gone so far as to coat the aircleaner base and lid with a soundproof coating, and I even run a separate air filter inside my 14" filter open element! 2 filters for cryin' out loud!
I mean, with the windows up and the a/c blower on high, I can still hear it.
Could this be an IAC problem? Best/easiest way to check IAC operation?
Any other thoughts?
Thanks, SC

vjo90RS8

iTrader: (1)

mine does this too, isnt it just the air and fuel being sucked into the intake?

Sonar_un

Yep, its air being sucked into the intake. It is especially noticable when you have an open element.

Man I love that sound.

super chevy

Perhaps.
I've built a lot of carb engines and none of them made this much noise - even sucking air through a 4 barrel.
I thought maybe the IAC was not operating properly and contributing to the noise.
SC

Pablo

iTrader: (1)

its extra fuel
remember the fuel is coming out of the injectors at a decent pressure and shooting directly onto the throttle blades (or on the edges if youve set your TBI up correctly) Much like the sound water makes when you put your thumb over the end of a garden hose. When you tip in the throttle its most noticeable because that action initiates the fuel addition for delta TPS (a change in TPS) and delta map (change in map) the delta tps is equivalent to a pump shot ona carburetor and the delta map is more or less equivalent to a powervalve in a holley. All that noise you hear is the extra fuel being dumped.

Its one of those things you are going to have to deal with unless you want to fabricate a silencer to go inside of the aircleaner or a snorkled aircleaner.. something with like two 3" snorkles like the ram air box will maintain performance and keep the noise level down.

Personally, i think you just need a louder exhaust

Pablo

iTrader: (1)

btw carburetors dont make this much noise because most of their fuel is introduced under the throttle plate at low throttle (via the idle circuit and then through the transfer slot )openings and only begins to be introduced via the boost venturi at increasing openings. So fuel isnt really getting sucked past the blades ever or squirting right onto the blades.. neither is it at 10+ psi when it comes out

super chevy

LOL, my exhaust is loud!
Sets off car alarms all the time what with the 40 series Flowmaster and downturns 18" behind cab.
In fact, the truck is nicknamed "white thunder" because it's loud as opposed to "white lightening" because it's not that fast
I have thought about fabbing a dual snorkel air cleaner, and probably will because that noise just bothers me.
Thanks, SC.

forsaken_one

If it is a really high pitched whistling, then it is that vacuum leak I was telling you about. It is due to the adapter plate having bores that are larger than the throttle body. and the gasket isnt getting clamped down.

super chevy

It was this noisy before I put the performer intake on.
It became much more noticeable when I put the "helix bore" tbi spacer on about 6 months ago. I was hoping to get rid of the spacer when I did the intake swap, but found I still had to use it to get the tbi - specifically, the IAC - to clear the EGR valve.
It must be a combination of spacer and big open element air cleaner that is contributing to the noise.
I'm going to build me a dual snorkel ram air cleaner of some sort to quiet it down.
SC

dimented24x7

iTrader: (2)

its just air and fuel being sucked into the tb. There are actually small orifaces just above the tb plates. Those probably make quite a bit of noise as the fuel and air pass through them

AUTOGON350

iTrader: (8)

I am using a throttle body from a 7.4L truck and the noise is insane. I spent a long time serching for leaks and found nothing.
It seems to me that a large portion of the noise comes from the IAC and the holes in the wall of the throttle bores.
I also found that the vacuum lines on the front of the TB have an effect on the sound. Im still not sure why that is.

dimented24x7

iTrader: (2)

since gm origionally intended these tb's to be used on utilitarian things like pickups and such, i dont think they gave sound control much thought.

AUTOGON350

iTrader: (8)

Once I was sure that it was not a vacuum leak I thought it was kinda cool.

If its too loud your too old right?

super chevy

There's nothing cool about a loud whistling sound coming from beneath your hood - unless you're running a blower or turbo.
I've been checking out the dual snorkel RamAir box from www.ramairbox.com . It looks like the solution to my problem, and I may be ordering one.
SC

Robinson1969

Good afternoon and my name is Jeffrey and I have a 93 Chevy Silverado 5.7 which I am Experiencing high idle & that loud hissing coming from my throttle. Please help I was also told that it's a vacuum leak was unable to locate.

OrangeBird

iTrader: (1)

Hi Jeffrey,

This forum is dedicated exclusively to 1982/1992 Pontiac Firebird/Chevy Camaro cars only. You'll need to find a generic Chevy forum (or one that deals in all chevy small block engines) for your answers.

I will give you this one tip; If spraying carb cleaner all around the TB and intake manifold while it's running don't find it (by the increased RPM when you spray near the vacuum leak), then you'll need to do a "smoke test".

I wish you luck with it

Schurkey

Connect a scan tool, find out what the IAC is doing.

First Guess: IAC is open too far, causing lots of noise and also causing high idle speed.

Maybe the IAC is defective. Maybe there's a wire-harness problem. Maybe the computer is faulty. Lots of possibilities. Start with the scan tool.

ironwill

IN before Oran..................nvm.

OrangeBird

iTrader: (1)

I do feel bad sending Jeff to another forum, seeing how he has an SBC, , , and to be honest if we had a "general SBC questions" area I'd be ok with that