ACE 350 Header Hiss
 

I'll try to keep this short (super long) and to the point.

Installed brand new ACE 350 Headers with OP with the gaskets they came with on a nearly stock 2018 MT BRZ (has a drop in filter) with 14k miles. Torqued everything down nicely, took my time. Tuned by Xero-Limit, cars runs flawlessly with no odd vibrations or problems. Tuner did not see anything unusual that would indicate a leak. The only weird thing I have been slightly annoyed by is this "hissing" or slight "fluttering hissing". I only experience this on acceleration when in gear. It is louder when the car is cold than when it is hot. The further I depress the pedal when in gear, the more prominent this sound becomes. It is especially prominent when surrounded by walls for the sound to bounce off of. It clearly sounds like it is coming from the engine bay area, most likely at the exhaust (headers/op). I will do a sound recording of it and post it up soon enough to get a better idea.

Initially, I figured it had to be a leak. Went under, checked everything, tightened everything. Nothing changed. Since then, I have been under the car 5 times to tighten stuff up. A couple of the times I completely removed the bolts/screws to loosen the exhaust, and redid the tightening process. Still all the same.

I'm starting to fall off the idea that this is an exhaust leak as the car runs beautifully. I have done plenty of reading on the fact that thinner headers can produce this kind of sound, which leads me to believe that might be it. I am mainly calling out the ACE header owners for this car to see if this is the case? With the popularity of this header, I would have expected more people to have mentioned something about this, but I am finding very little to no information. I also contacted CSG about this and have not gotten any general answers yet on whether what I am experiencing is normal or not.

I have a similar wooshing sound and if it's anything like my old Cosworth headers, it's just rasp.

+2 for the exact same thing you're talking about. It appears some headers just make that noise and it sounds like an exhaust leak. I have literally investigated this issue to death on my car with no luck.

yep its a sound that sounds like it is coming from under your dash and it starts at like 3-4k rpm

I have the same sound from my A350. Its just the way it is

Great, thanks for the confirmation guys. My plan was to get a cat-back to help the tone - Touring86 to be more exact. I assume this will maybe help overcome that noise, but not get rid of it, correct?

I have Ace350 with the Touring86 and Ace front pipe. Initial install was a little loud for my taste and had the noise as you describe.
My wife didn't like the smell of a cat less set up and even with the Touring86 catback it was a bit loud for my taste so I dropped the Ace front pipe and put the stock pipe with the cat back on. Surprisingly it sounded way better and the exhaust leak noise disappeared.

No idea why

That's normal for how the header sounds.

Is it similar to a whistling sound? I'm noticing that with my new header install. Although instead if the Ace I have the catless Tomei EL.

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+1 for Normal sound

Yes, in a way. Hissing/whistling with maybe a slight bit of flutter, but not really. So your case is probably similar. This is sort of my first time dealing with headers, so I was not very familiar with this sound yet. From watching videos of header sounds, I never picked up on this sound so I thought it was unusual when I first heard it.

Good to know. I would assume because the air is more free to flow without as much restriction, that less hissing sound is produced at the headers since less air gets backed up maybe? I have no idea haha, but I am happy to hear that this will be a good combination for the exhaust. I definitely read about the front pipe making it really loud since the whole car is cat-less, and this is not my intention for this car, so I will stay away from going that route.

Well, I'm reverting back to the stock front pipe from my HKS. I'll be curious if the rasp is worse or same. I would say better but, the HKS R-Spec front pipe is pretty quiet.

Should become better if not disappear as more restriction will muffle it more anyways. Most people on this forum have good luck with a header and cat-back with little to no rasp depending on the combination. The mid-pipe, unless well resonated, definitely creates plenty of rasp once cat-less.