[Eric_Oz_S2]

I am using the same supercharger unit as the d1r kit (rotrex c30-94). With mine I am running an 85mm pulley which puts the internal rpm close to its limit at the rev cutout point. When driving on this street you can barely hear the supercharger. However, on the track the unit (apparently) screams like a banshee over about 5000 rpm. In fact, at the track I have been pinged at about 115db. Spectators tell me it is a really loud scream as the car passes at high revs. Inside you can only hear a whistle.



I'm interested if anyone else has tracked their car and had similar feedback from trackside spectators.



Any ideas on how one might reduce the noise level?

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[Dubai944]

Jaycar sell some decent noise reduction mat that is adhesive on one side. I used that under the hood above the supercharger and on the guard panels around the supercharger and it did drop the noise a bit. Are you sure it's the supercharger noise that is causing all the decibels? Induction noise caused me some problems at Lakeside until I boxed up the intake filter. Exhaust obviously, but probably not on your car.

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[Eric_Oz_S2]

Well I'm about to pull the afm and replace it with a <acronym title='mass air flow'>MAF</acronym>. Some have suggested that the airflow through the afm is causing excessive whistleing. I'm running a cone filter which is mounted in front of the left wheel liner right behind the front bumper cover. Might try some of that noise dampening matt as a start.

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[flash]

you likely have an intake restriction that is limiting the airflow into the supercharger. the supercharger will continue to try to compress the air, even though the supply is too small. this produces the screaming you hear



you would be amazed at how important the intake side is

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[tamathumper]

Not having driven a supercharged car with a K&N before this, I'm curious what it *should* sound like? Of course with all that high-RPM air-eating going on up front, my car makes some additional noise now that the D1R is installed, but is it normal? With no other examples around, I have no way to tell. And with only me driving it, I don't know what it sounds like outside the car.



There's no good way to describe the noise I hear inside the car - it's not there at idle or below 2,000 RPMs, then between about 3,000 and 6,000 it becomes a whining, then whooshing, then whistling, then scraping/shearing, and finally screaming noise to indicate maximum air velocity. All of which to the unaccustomed ear can be quite concerning. <img src="/forum/images/smilies/968/unsure.png" class="smilie" alt="" /> From revving it with the hood open, a lot of the noise comes out of the K&N, so I'm guessing the original air box was good at keeping some of the noise in?



At least there's no visible belt rubbing, and the supercharger oil is remaining steady, and the car still goes like stink. <img src="/forum/images/smilies/968/biggrin.png" class="smilie" alt="" />

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[ds968]

I can't say that I hear any difference ( vs my former NA engine sound ) from inside the car and with the radio and air off of course. If I open the hood and rev the engine by hand to roughly 4 k rpm or so, there is a air " whoosh " note that's a bit more discernible but nothing too loud. Only when I get to around 6 rpm while driving , then there is the screaming banshee sound that everyone is talking about. BTW, being a native-American linguistics historian, in screaming banshee language that yell translates to ". Better shift now, pale face ! "

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[tamathumper]

That concerns me, as compared to yours, mine would be very loud indeed!

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[flash]

lol - in a cab, i'm surprised you can hear anything until the scream.



the whining sounds like the belt might be too tight. it should not be as tight as the stock belt. if you over-tighten it, the driver side upper idler pulley bearing will fail, and it will make noise.



whooshing? you sure that isn't the air blowing through your hair?



whistling should really only happen off throttle when coming off boost.



the scream we already know about. that's the built in "shift you dummy. there's no more power beyond this point" indicator.



hope that helps

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[MB968]

Eric, if this is an intake restriction, I'd fix that first.



My experience has only been with roots type SCs. On them, running 12,000 rpm with a three lobe rotor gives a vane pass frequency of 600 Hz, which I always found pleasant to my ear. Does the noise that others hear match the Rotrex's vane pass freq (just the rpm times the number of blades/fins on the compressor divided by 60)? If it seems much higher than that, I'd concentrate on the intake restriction which could cause a much higher whistling noise.



If you find you need to abate the noise, I'd suggest an alternative to the use of the damping mat. A mat sytle would typically be used to dampen the (in our case) sheet metal that it is applied to in order to minimize it as a speaker. If you are dealing with intake noise, which I expect is the case, the mat may give very little benefit. Fortunately high frequency noise is easier to control than low freq. There are a number of available closed cell foams that serve to trap the noise in the foam. Especially if the noise source has to turn a corner to get out into the surrounding area where it will be heard, the use of this type of foam lining the exit duct for the noise can be quite effective. We used to purchase a lot from EAR, but I'm sure you could find other sources.

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[flash]

do not put ANYTHING on the hood. it will seriously increase the under hood temps. i've tried everything i can find, and NOTHING works without increasing the heat.

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[ds968]

[quote name='flash' timestamp='1367592382' post='142236']

do not put ANYTHING on the hood. it will seriously increase the under hood temps. i've tried everything i can find, and NOTHING works without increasing the heat.

[/quote]





+ 1 !

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[MB968]

Yeah I agree, not on the hood. Not only because it will keep in heat, but because generally these materials are flamable, unless you pay the premium to get flame retarden ones.



Since Eric's air filter is mounted "in front of the left wheel liner right behind the front bumper cover", this would be the area to concentrate with any noise absorbtive foam and any channel the air has to take to get to this area.

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[Eric_Oz_S2]

Here is a link to a video where you can hear the sound on the track. Look at the tacho at the start. This is in fourth gear, peaking at about 6500 rpm, 190 km/h.





http://www.youtube.com/watch?v=XiYjVqLdqn0





Is this the same sound that you are all hearing?



Do you think the sound would be emanating from the head unit or propagating through the intake? With regards to dampening this sound, I obviously cant place anything in the front. I can only put sound matting on the side of the bumper cover and inside the wheel liner. Not sure if this would help much.



WDYT?

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[tamathumper]

Yes, that's similar to what I hear. I've been searching for a good mic for the iPad or my Samsung phone, and I'll post a recording for you if I can get one.

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[MB968]

Eric, I'd send your noise video to the engineers at Rotrex. They should be very familiar with the noise characteristics of the unit and could help decide if it was the body of the unit acting like a speaker to create this noise, or the noise eminating out the intake. To me, it sounds like way too high a frequency to be structure born, that's why I'm thinking it is coming from the intake.

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[flash]

hmmm - i can't see the link

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[SanderSchippers]

Here's the link Flash: Click

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[flash]

that actually sounds like an idler pulley bearing going out. you can hear the intake restriction just before the noise gets loud, but the metallic high pitched sound is like what the idler pulley bearing sounds like just before it goes.



a test would be running it up that high in rpm while sitting still. you won't hit much boost, so the compressor won't make the screaming noise. if you still hear the noise, then you almost certainly have something else going on.

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[rxter]

In a cab I have a whistle all the time from engine on to engine off. Sounds like a tea kettle. We also hear what sounds like a lot of air getting sucked in above 4K. Below 4K just the whistle.

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[ds968]

I paid a bit more attention to the sounds after reading this thread, and there is a whistle when coming off boost but barely audible really..

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