What does an exhaust leak sound like?
 

I recently installed an OpenFlash Header on my BRZ, and I'm wondering if it might be leaking. The symptoms are: On cold start, for about 20 seconds or so I hear a popping noise, almost like a 2-stroke engine. It also makes the same noise when idling, sometimes but not always. Once I increase engine temp and/or exhaust pressure the noise goes away.

Other than the little popping noises the car seems to be performing like a beast. I also changed the inlet tube with a Perrin and tuned for E85 with OFT OTS stage 2 tune at around the same time. I tracked the car this past weekend and it felt like a monster (for a BRZ anyway.) I passed a couple of Vettes and Porsches without issue. I was in the noob group though so skill level was all over the place.

Anyway, does this sound like maybe I just didn't tighten down the header properly? Or maybe something else? I'm going to get under it tonight and back out the bolts / nuts and re-torque them. Just thought I'd inquire with you folks to see if maybe I am missing something. Thanks.

An exhaust leak is literal exhaust coming out of a hole/crack/gasket somewhere in the exhaust system. If there is noise coming from the header, its a leak, if the noise is coming from the exhaust tips, then you're probably fine.

It's not a bad idea to re-torque the bolts after some heat cycles anyway though.

Yeah it's definitely coming from the engine bay, not the exhaust tips.

You changed a lot of things at once, so pinning down root cause is tougher. Have you ever run E85 previous to this? Some people claim they get odd noises from the fuel pump when running it. If it was an exhaust leak, it definitely would not go away with more exhaust pressure. The tune may also have a different warm up set than you're used to.

Is it possible to capture this in a video and share with us?

It kinda sounds like a loud flapping sound. That’s the best i could describe it.


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FWIW, I thought I had an exhaust leak when I installed my ACE header, but I looked around and couldn't find any usual, obvious signs of a leak (no soot marks by the flanges). Then I asked my friend to sit in it and he told me it sounded the same as his. Turned out the much thinner metal, and lack of heat shields, just allows a lot more noise to come through, which in my case is a ticking noise that sounds a lot like a small leak somewhere.

This ^
Headers make weird noises sometimes. As said the metal is usually thinner and the different bends make the flow sound strange. If uncatted or before the cats you will smell it pretty easily if it is indeed a leak.

Nope.

Yeah as soon as I get home.

That seems like what I'm hearing. Imagine a huge whoopee cushion and a real fat guy sitting on it very slowly.

That's possible too that it's just the natural sound. Also I still have all the underbody removed (the fiber piece and the metal skid plate.)

I don't smell anything unusual.

Just a note, I did the E85 tune and the inlet tube about a week before the header, and didn't notice any noises during that week.

Put those underbody panels back on. You'll be surprised at how much sound they block.

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It'll make a loud ticking sound for only that one or two cylinders if the leak is at the exhaust port.

It'll make a more poofy sound on all exhaust strokes if it's downstream.

Waiting for the vid. :popcorn:

When I first installed my aftermarket header I was trying to discern all the different sounds. 1) the whooshy exhaust sound was due to thinner metal and no heat shield, and the general design of my header.
2) I experienced a flapping, tractor sound coming from the engine bay on cold start which did not sound right. I was lazy, and ended up not bothering to get back under, instead I went to an exhaust shop and said I had an exhaust leak.

When I got the car back from the shop they said one of the nuts from one side of the exhaust runner flanges had come loose. (It created a very small gap between the gasket and the flange) They ended up using loctite to correct it. Some of the exhaust header designs make it difficult to apply the correct torque settings to both sides of the header at the attachment point, and I theorise that when you run the car, especially when lubrication has been applied to the bolt/nut, it vibrates the nut loose.

My car has been running perfectly for the last 4 months or so once this occurred.

Hope this helps.

When I had a leaky gasket between a front pipe and a catback, the sound was more farty and VERY noticeable when you turn the car off and the last bit of exhaust gases are expelled. It's almost like the car blows a raspberry at you. PPFFFRRRT

Still popping, haven't had a chance to do anything, been super busy the last couple of days. Will try to update tonight.