Classic/Antique Car Repair: MUSTANG, cobra rims, cold air intake

Question
My 96 mustang GT has a hissing vacuum like sound coming from
the passenger dash when i accelerate. i also have 2 1/2 inch X pipe installed, since the hissing sound i have lost the original "tone" of the exhaust., these are the symptoms of my mustang currently and i am attempting to find the source with no avail. i also loose alot of torque when the hiss sound comes (as i accelerate) any help on what this is would be greatly appreciated. - thanks john

i have a 96 mustang GT, cold air intake, 70 mm accufab throttle body, 2 1/2 inch x pipe w/ high flow cats, out to dual mac exhaust pro chaimbers. Cobra rims.


Answer
With engine running at idle, spray carb cleaner all around the outside of the engine. Spray intake edges and behind engine. When engine speed changes, you have found your leak. Using a spray with the tiny directional stray helps.

If there is no reation to eternal spray, one of your intake gaskets is restricting a port.