# What exactly is the phenomenon that occurs on a supercharged muscle car to make this sound at idle?

**URL:** <https://boards.straightdope.com/t/what-exactly-is-the-phenomenon-that-occurs-on-a-supercharged-muscle-car-to-make-this-sound-at-idle/828824>\
**Category:** Factual Questions\
**Created:** [February 2, 2019, 6:08am UTC](https://boards.straightdope.com/t/what-exactly-is-the-phenomenon-that-occurs-on-a-supercharged-muscle-car-to-make-this-sound-at-idle/828824 "2019-02-02T06:08:08Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![SHARKBITEATTACK](https://avatars.discourse-cdn.com/v4/letter/s/91b2a8/32.png) [@SHARKBITEATTACK](https://boards.straightdope.com/u/SHARKBITEATTACK)\
**Post date:** [February 2, 2019, 6:08am UTC](https://boards.straightdope.com/t/what-exactly-is-the-phenomenon-that-occurs-on-a-supercharged-muscle-car-to-make-this-sound-at-idle/828824/1 "2019-02-02T06:08:08Z")

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take this video for example [Big Cam BLOWER SURGE Supercharged 1967 Camaro SS "CRUSHER" Start Up Leaving MCACN Muscle Car Show - YouTube](https://www.youtube.com/watch?v=1w9_bzxCdsc)

The way the engine sort of revs up and then exhales, what is this? I’ve always referred to this as blower surge but someone recently challenged me and told me its just the duration of the cam and all its doing is loping. Is this different from reversion back into the intake valve is open as the piston travels up past 180 degrees? Does it have to do with the intake and exhaust valves being open simultaneously for a period of time? (overlap) manifold pressure building and bleeding? something else?

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**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\
**Post date:** [February 2, 2019, 7:26am UTC](https://boards.straightdope.com/t/what-exactly-is-the-phenomenon-that-occurs-on-a-supercharged-muscle-car-to-make-this-sound-at-idle/828824/2 "2019-02-02T07:26:24Z")

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Blower surge. A good explanation here:

> **[TECH QUICKIE: Cool or Not--What is Blower Surge?](https://www.enginelabs.com/news/tech-quickie-cool-not-blower-surge/)**
>
> Do you think blower surge is cool? Do you know why some supercharged engines surge at idle, and others don't? We have the answers and some cool videos here!

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**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\
**Post date:** [February 2, 2019, 4:20pm UTC](https://boards.straightdope.com/t/what-exactly-is-the-phenomenon-that-occurs-on-a-supercharged-muscle-car-to-make-this-sound-at-idle/828824/3 "2019-02-02T16:20:14Z")

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I can smell that whiner’s rich exhaust from here.

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**Author:** ![Littleman](https://avatars.discourse-cdn.com/v4/letter/l/ccd318/32.png) [@Littleman](https://boards.straightdope.com/u/Littleman)\
**Post date:** [February 2, 2019, 5:12pm UTC](https://boards.straightdope.com/t/what-exactly-is-the-phenomenon-that-occurs-on-a-supercharged-muscle-car-to-make-this-sound-at-idle/828824/4 "2019-02-02T17:12:24Z")

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It’s blower surge, not loping. Though the two are closely related since both cyclically change vacuum  
or manifold pressure which in turn cyclically changes rich to lean to rich to lean.  
Both are just idle hunting really with a different cause.