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Supercharger Flutter

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Old 01-09-2017, 12:07 AM   #1
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Default Supercharger Flutter

HI all,

As most of you will know i have recently finished installing my HKS super charger and i understand the flutter noise is fairly normal as i release off the throttle. My concern is, sometimes the flutter seems to go on for a long time, almost as if something is stuck open. The noise only seems to go away when i get back on the throttle. I find it occurs after accelerating hard up to about 70mph and then lifting off and continuing to cruise around that sort of speed. Is this normal or is there something i need to get sorted?

Thanks in advance

Steve
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Old 01-09-2017, 12:22 AM   #2
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Its normal, at least in comparison to my HKS, so if it isnt, mine is broken too lol.

Happens on my car after every hard pull, but goes away straight away as soon as i press the throttle, even slightly.
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Old 01-09-2017, 12:35 AM   #3
 
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There might be some confusion about what flutter actually is. I interpret flutter as when the supercharger cant dump the pressure so it the boosted air starts to go back through the supercharger. This is very bad for the supercharger and the belt system as its trying to force the supercharger to rotate the opposite way.

When cruising at light throttle the supercharger still makes pressure but this should be dumped by the bypass valve on the intercooler pipework back into the inlet piping next to the air filter. Some of this will come out as noise as effectively its a large air leak. Its noisy and should sound more like a boost leak. If you fit a vent to atmosphere bypass valve then this noise is even more pronounced as even on light throttle the bypass valve will whistle away as it dumps the boosted air that the engine doesn't need.

On high throttle the car will make lots of boost pressure and as soon as you shut that throttle the air has to go somewhere. It will be dumped by the bypass valve which will open by the vacuum being produced by shutting the throttle. If this didn't happen then it would damage the supercharger or snap the throttle plate off. Superchargers produce boost based on RPM so if you lift off the throttle at 8,000 rpm then you have tons and tons of air that will need to be constantly vented otherwise it will damage something. This is why a lot of the NOVI supercharged guys use a dual BOV system to ensure that this air is vented without applying any pressure on components. I use a 34mm turbosmart valve on my HKS which seems to do the job fine and makes a nice whoosh when I let off the throttle.
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Old 01-09-2017, 12:44 AM   #4
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with the BOV that comes with the HKS i have never had a Woosh type sound, its always flutter, theirs a time attack car with the HKS supercharger kit on it also, and that flutters the same as mine, so i took it as being normal?
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Old 01-09-2017, 01:47 AM   #5
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It flutters for you because it hasn't been plumed into the intake... Mine has been so I don't get the loud annoying flutter noise, i find it a bit asbo :P instead i get a nice pshhhh noise... i do love the noise descriptions you get on here
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Old 01-09-2017, 01:52 AM   #6
 
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Quote:
Originally Posted by Define198 View Post
with the BOV that comes with the HKS i have never had a Woosh type sound, its always flutter, theirs a time attack car with the HKS supercharger kit on it also, and that flutters the same as mine, so i took it as being normal?
The whoosh i get is the air being recirculated and the noise comes out of the air filter area.

I never had flutter with the HKS pipework. Just a strong noise on gearchange. I know someone else with the kit who has also said he got what could only be described as flutter. Any chance you could get a video of it happening? I will do a video later of the engine being revved and the noise i get when the pressure is being released.
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Old 01-09-2017, 01:54 AM   #7
 
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This is the best description of the type of flutter im talking about

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Old 01-09-2017, 02:05 AM   #8
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From what i remember if i rev the car while stationary i dont get the flutter noise, its only when driving

It sounds a little like that, but that car sounds a bit broken, imo the flutter on hks kit sounds rather good

Last edited by Define198; 01-09-2017 at 02:19 AM.
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Old 01-09-2017, 02:39 AM   #9
 
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https://www.youtube.com/watch?v=KtRe...ature=youtu.be

I have managed to make my supercharger flutter when a vacuum line wasn't connected properly and it sounded very much like in this video but i knew this wasn't healthy and quickly shut the engine off and fixed the issue.

I really wouldn't feel comfortable with having the supercharger flutter because its suggest that the bypass valve isn't able to relieve enough pressure. I would be tempted to check vacuum line to the bypass valve and that the bypass valve is assembled correctly.

The bypass valve should be dumping air at idle and light throttle it should only close when your pushing on and getting on the power.
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Old 01-09-2017, 03:00 AM   #10
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My flutter sounds exactly like the one in the video when letting off the throttle at high boost, like I said it is not doing it if I blippe the throttle under the bonnet, so it's not as extreme as his, I am 99.9% that I set it up exactly how hks said to in the manual so if theirs a problem it's most likely in its design?
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