UGH! Pffft/Pssst noise diagnosis help/comments appreciated

[PhoenixGTS]

Weather has been nice so windows have been open a lot. Car has been running great. This morning on the way to a mediation I start to hear a faint pffft/pssst exhaust leak sound. It is a brand new sound. Gets louder and louder over the 20 miles journey. Sounds like header-to-head gasket on passenger side. What worries me is that I open the hood and when I tried to verify where it is coming from I cannot, and it sounds like it is from inside the top of the engine - like a valvetrain issue. However, on the way back on the freeway, I notice that it only makes the pffft/pssst noise when you have throttle on and does not even at the same rpm when you have the throttle closed down - that has to mean exhaust - right? At a given rpm, if it was a valvetrain issue it would occur no matter what the throttle input - right? Oh please be an exhaust leak!

 

[Randy]

Is it only under 1/4 to maybe 1/3rd throttle, and a kind of high pitched squeak type sound? If so, thats a known side-effect of smooth tubes. Otherwise, no idea.

 

[PhoenixGTS]

It is not continuous. It is only on one cylinder so it is every second revolution and dependent on rpm. So either an exhaust leak of possibly a rocker arm, but if it was a rocker arm it would be during coasting at zero throttle input - which it is not.

 

[Jerry Scott[CO]]

It's likely a gasket leaking on the Belanger headers. Put the car on jack stands and allow the exhaust to cool over-night. Start the engine and check each junction by placing your hand near each bolted joint. Do this before the exhaust gets hot. You should be able to feel where it is leaking. When you find the leak, you will need to take the pipe apart at that joint, clean off the old gasket and replace with a gasket made of graphite and steel. Do not use a composite material gasket as this will likely burn out again. Also seal the gasket with Permatex Copper Ultraseal. I had trouble with the two bolt flanges on my B&B copy of the Belanger headers, but finally got it to stay fixed with this approach. For the three bolt flanges, I used a solid copper gasket with Permatex. You also may find that one of the flange bolts has come loose.

If you let this go too long, the leak will gas cut the flange and make it even harder to seal.
Jerry
Jerry

 

[PhoenixGTS]

If you let this go too long, the leak will gas cut the flange and make it even harder to seal.
Jerry
Jerry

Yep. Once I get home, I'm not driving it until it is fixed. Had not thought of the header mid-flanges as being the culprit since it was my understanding there is no gasket in those. Still thinking it is the head-to-header, but I will make a stethescope out of a piece of ruber tubing when I get home and narrow it down.

Is there any chance that a failed intake gasket could make such a noise? I cannot see how since it is never pressurized and it sure sounds like escaping gas under pressure.

 

[PhoenixGTS]

Cut a three foot length of 3/8" ID hose, stuck one end in my ear and moved the other end around the suspected areas. This test tells me my leak is the center cylinder on the passenger side (#6 I believe). All mid and final flange bolts are intact and tight. From what I can see through the hard heater coolant lines the gasket looks fine. The injury to the gasket must be very small.

So what do you think? Switch from the Belanger provided composite gaskets to the stock gaskets? If stock, is there any chance they have smaller bores and would cut into the flow going into the 1.75" header tubes? Lou will give me another set and I would use those if the stockers are too small. What about chemical sealant? Is there some sort of ultra-temps silicone for this application (someone above mentioned Permetex)?

 

[Jack B]

If you used the Balenger supplied gasket, that explains it. They have a very short life.