I'm going crazy over here. Full background story

3 weeks ago we installed a used set of Hedman shorties and Y pipe with an old Catco converter. Temporarily cobbled it to the stock 2.25 pipe(waiting on parts) Gaskets for the headers were Felpro MS 9275 B. Collector gaskets were Spectre 431 (compressed ceramic fiber)

Immediately started hearing an odd squeeking and what sounded like a leak under load. Squeek/squealing and tick tick tick tick.

Double checked everything didn't seem to be any leaks present. Used some Permatex copper RTV around the collectors and where the Y joined the pipe to maybe help. Nothing.

We thought that maybe because the converter was "half hollowed out" might be that. Fingers crossed

The rest of my exhaust showed up and we installed it. 3" Magnaflow cat, Walker 46669 pipe and a Magnaflow muffler. Noise still present.

Today we changed the collector gaskets. Of course the ones we removed looked fine. Just for fun started the car with just the headers and heard the squeek. Hmmmm. Installed the new copper gaskets and.... Still there.

In park you hear it a bit giving the car little shots of throttle. Under load if I feather it barely noticeable. As soon as I accelerate normally it's back. I just don't get it. The header bolts are tight and I don't see any leaks at the headers. A friend is lending me a smoke machine to try and find anything.

My friend who helped with install (actually did most of it haha) thinks maybe the headers themselves are too thin and this might be normal. Idk about that.

I'm getting severely discouraged. I honestly didn't even want to do this. My plan was to get the bigger stock manifolds and run a Magnaflow y pipe but I caved into the peer pressure sighhh. Like the extra 10 hp is going to make my TBI wonder rip up the streets.

Please help lol!

 

Get Remflex header & collector gaskets. They are the best gaskets and the only ones that will last!

 

It could be the cats. I remember when my friend hollowed out the cats on his 5.0L Mustang back in the 90s, it made a sound like stuff rattling around in there (no matter how much he tried to get every last bit out). I guess you could have characterized it as squeaks at times.

It wasn't until he replaced the cats with straight pipe did the noise go away.

 

I doubt it's cat converter. We said maybee with the ****ed with converter that was originally on the Y pipe but no way with a brand new unit. We weren't going to make a scene when we ran it open headers but I heard it for a second when the car started.

My Mustang has 2x high flow cats and makes zero funky noises.

 

Any chance there’s a broken weld at the collector?

 

Who knows at this point. Let's see what happens with the smoke test.

 

Because I haven't seen it mentioned , , , I figure I gotta be the one to ask , if perchance this isn't an exhaust leak ;

Are you 101% certain one of the headers isn't too close to some part of the body , that it touches when the rubber engine mounts allow the engine to flex slightly when you hit the gas ?

 

I can answer that with about 90% confidence haha. Nothing seems to be touching drivers side. On the pass side the Y is a little close at the bottom corner (near the wheel I guess). I can't say for sure it isn't touching when under load. Will report back soon.

 

Make sure the spark plugs are tight.. Odd but had something similar happen to a friends car.

 

I'll check it out, thanks for the suggestion. We did change the plugs while doing the headers so who knows. I did smoke test the car and had nothing.