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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain. |
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05-13-2021, 04:13 PM | #1 |
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Exhaust Hissing when in lowering rpms
Hey guys, so I have been hearing this sound for a while now and always thought it was an exhaust leak, but after many hours of looking for said leak and not finding one, I ended up taking it to an exhaust shop and having them take a look at it. It turns out I was right, and there is no leak. So the sound I'm hearing is when I'm accelerating in the lower RPMs I can hear this hissing sound whenever I am driving next to a wall or something like that. I have a gruppe-s catless uel header and a perrin Catback. This sound goes away when I put my stock header back on to check, so it makes me think it could be just rasp, but when I have looked into that header catback combo, I've only seen people been saying it has zero rasp. Does anyone have any input on what might be going on?
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05-13-2021, 04:36 PM | #2 |
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I have the Tomei UEL header, a overpipe, and a motive front pipe with stock catback, I do hear the noise, it's the exhaust AVCS activating, you can try tuning the overlap or let it be
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The Following User Says Thank You to Project_1796 For This Useful Post: | Dububster (05-13-2021) |
05-13-2021, 06:19 PM | #3 |
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Oh, interesting, I had no idea that was a thing. I really appreciate the insight.
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05-13-2021, 06:21 PM | #4 |
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A head without insulation can make a hissing sound. Eventually my head failed, and it was a totally different effect.
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05-13-2021, 06:34 PM | #5 |
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05-13-2021, 09:14 PM | #6 |
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Dunno. I never tried that with the stock header. Possibly. Probably if you take out the cats. Also more likely with thinner metal aftermarket heads. On my gen 1 Borla, it was super noticeable. Sounded like snakes.
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05-13-2021, 09:53 PM | #7 |
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AVCS is almost like Honda's VTEC system but activated by different means, subaru has the ability to control both intake and exhaust camshaft timings on the FA20 for valve overlap, depending on the exhuast manifold design, the engine noise & exhaust note will sound different depending on how it's tuned. The stock exhaust manifold is more of a equal length design, so when you place it back on noise goes away.
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05-14-2021, 02:08 AM | #8 | |
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05-14-2021, 02:18 AM | #9 |
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What do you exactly mean by not insulated head? And would there be any other symptoms of that?
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05-14-2021, 02:34 AM | #10 |
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[QUOTE=Dububster;3432453]Gotcha, I'm very happy to hear it's normal. I have my car tuned with the oft. Would that affect it https://www.comeanddriveit.com/engin...avcs-explained
Here's more info on the avcs system. There's also a post here on the forums about different cam profiles for exhaust manifolds. Take a peek here at steve99's tune tweaks under avcs section https://www.ft86club.com/forums/showthread.php?t=74754 |
The Following User Says Thank You to Project_1796 For This Useful Post: | Dububster (05-14-2021) |
05-14-2021, 10:30 AM | #11 |
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Same here. I bought my FR-S with gen 1 Borla UEL's and replaced them with Tomei UEL's when the flex pipes went and with both it has hissed when off throttle and coasting. Can't hear any other time because 3" Greddy Catback go brrrr
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05-14-2021, 01:14 PM | #12 | ||
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05-14-2021, 04:29 PM | #13 | |
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05-14-2021, 05:11 PM | #14 | |
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