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CTSC source of whining or how to quiet it down

goldNSX

goldNSX

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Joined
15 May 2004
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6,898
Ok, here we go with the next question most people shake their head but there's a reason why I ask:

We have very strict regulations on how loud (dB) a car is ought to be. Regarding the loud whine of the supercharger under load as I've seen on youtube videos it's too loud to pass the tests.

- What is the source of the whining? Air loading in the charger? Charger bearings or driving belt?

- Depending on the source HOW to dampen the noise?
 
The Whipple charger spins at 12000+ RPM and that coupled with suction and compression of air creates that sweeeeeeet sound:biggrin: :biggrin:

I haven't tried these, but there are a couple of things that might help in reducing the db. Using a different oil may help . Amsoil has reduced my engine noise considerably, but I have not tested this on the supercharger.

You could also pursue a a thicker - or double pane - glass but you'd have to get a custom made and that's pricey.

Lastly, I am positing that having a larger pulley would prohibit the supercharger from spinning as high, with the cost of producing lower boost. It might be worth the trade-off though.

Anything beyond that and you'd have to invest in impractical and intrusive measures. Adding noise dampening material around the hatch and orifices and potentially and under tray beneath the engine will reduce the db count somewhat. This however is extremely impractical, intrusive, not without significant costs and risks (engine overheating etc..)
 
slownsxt said:
You could also pursue a a thicker - or double pane - glass but you'd have to get a custom made and that's pricey.
Click to expand...

That glass is already double paned unless it's a Type-R. I would imagine the sound would be measured outside of the car for any type of noise test.
 
The best solution to getting rid of the sound is to remove the unit and sell it to me. :biggrin:
 
Thanks guys, the problem is not the sound within the cabin but the sound emissions on the road. The test we have to pass is described here: http://www.admin.ch/ch/d/sr/741_41/app7.html
Sorry, in German but from the picture you should get the idea. Two micros record the sound pressure level of a car that drives with about 35 mph into the measuring field (+-10 meters from the micros), then thottles hard in a specific gear and passes the recording microphones. 8x dB are the limit.

According to the videos I highly fear that the measured dB's are much too high with the CTSC. And you hope you get the message too that we regard the US as a country where freedom is literally worth to live in. :)
 
I still think the exhaust is going to be the loudest part of your car. What kind do you have? Did it come with silencers?
 
Deltron Zero said:
I still think the exhaust is going to be the loudest part of your car. What kind do you have? Did it come with silencers?
Click to expand...

We have to do the test with the OEM exhaust. Every other one is simply too loud to pass the test, even the quietest ones. Under boost the sound pressure level naturally rises even with the OEM one. Also critical.
 
goldNSX said:
We have to do the test with the OEM exhaust. Every other one is simply too loud to pass the test, even the quietest ones. Under boost the sound pressure level naturally rises even with the OEM one. Also critical.
Click to expand...

Will holding the bypass valve open on the SC work?
 
Deltron Zero said:
Use a zip tie and hold the bypass valve on the SC open so the SC will not build any boost. There was another thread on here somewhere talking about this.
Click to expand...

They will detect this cheating for sure I'm afraid. We have to give them the car and they will test the power, the emissions and the noise with the same car. If all tests are passed you can legally drive with it on the road. As said before we maybe have the most restrictive laws all over the world to pass. :( The certification procedure will cost around $9k which can be divided between several CTSC installs.

Still asking: What is the source of the whine?
 
The whine, AFAIK, is the spinning of the charger itself. I dont see how the charger can be working without the whine...

Best bet is the zip tie Im afraid, or uninstall it.
 
The sound of my CTSCs has not been noticed by most of my car friends and therefore I feel they are quiet. I only notice a minor "sweet sound" when over 5500 RPM. But as to your question: "what is the source of the whining sound".
It is my opinion that the whining is coming from the beveled gears that over drive the rotors. This gearing increases the RPM the compressor's rotors spin at. The step-up or overdrive is approximately 150% if my memory serves me correctly.
The earlier suggestions of using the stock air box is a great one and experimenting with oil in the gear case is very good also; but don't go too far with the oil, there is a reason the manufacture recommends a certain viscosity and type of lubricant.
The drive snout may also be acting as a "sounding board", you might try wrapping it in a foam casing to help quiet things down. Changing the "sound deadening material" on the bottom of the engine cover may also have positive impact on reducing the dB's that are heard outside the car.
Best of luck and keep us informed.
 
I don't have a CTSC and that makes me the perfect person to diagnose the noise because my opinions are unclouded by facts. :smile: From what I remember, there is no clutch in a CTSC so it is always spinning. However, the whine only occurs when you depress the throttle far enough that the bypass valve closes and the intake air flows through the charger. The whine should therefore be one or maybe both of the following:
  1. sound waves in the intake air itself caused by the impeller which travel through the air filter and out through the driver's side air intake
  2. a vibration in the CTSC housing, belt, etc. which occurs under load when the charger is compressing air and which is transmitted to the air in the engine compartment as if through a speaker cone
If it's only #1, then a better insulated air intake and filter (i.e. OEM intake and filter) should quiet the car down nicely. If it's #2, um, it'll be more difficult.
 
You wil not here the whine of the SC over your exhaust outside the car. Stock or aftermarket. I have the Comptech Whipple on my car and I barely hear it in the cabin over the exhaust. Outside the car, Nobody has ever said they can hear the SC at full throttle. I'll post my dyno run later tonight
 
chudson1549 said:
You wil not here the whine of the SC over your exhaust outside the car. Stock or aftermarket. I have the Comptech Whipple on my car and I barely hear it in the cabin over the exhaust. Outside the car, Nobody has ever said they can hear the SC at full throttle. I'll post my dyno run later tonight
Click to expand...

I'm very interested. So did the 'flying bee' (http://www.youtube.com/watch?v=6LcQBhLAL5k) remove the air filter or something like that? The flying bee is an extreme example I know.

Concluding from the posts above can we say the the whine only occurs under boost and above 5.5k rpm?
 
I notice a whining sound coming from the air inlet on the drivers side when I apply the gas. I believe it is coming from the supercharger (Autorotor), possibly the meshing of the rotors and/or the gears. I don't notice it very much with the windows up, but with the drivers side window down it's quite noticeable when the throttle plate is open. It might be worth looking into some ways to dampen the noise inside the air filter housing. One idea would be gluing some foam to the inside walls of the housing, which unfortunately introduces the possibility of it coming off. You could probably fasten a screen of some sort over the foam to hold it in place. You might try a different type of air filter element like the K&N that fits in the stock housing, or some kind of baffle up stream of the air filter element that forces the air stream to reverse direction or interferes with the path of the sound waves in some manner. I don't know enough about acoustics to suggest anything specific.

John Crawford
 
john85259 said:
I notice a whining sound coming from the air inlet on the drivers side when I apply the gas. I believe it is coming from the supercharger (Autorotor), possibly the meshing of the rotors and/or the gears. I don't notice it very much with the windows up, but with the drivers side window down it's quite noticeable when the throttle plate is open. It might be worth looking into some ways to dampen the noise inside the air filter housing. One idea would be gluing some foam to the inside walls of the housing, which unfortunately introduces the possibility of it coming off. You could probably fasten a screen of some sort over the foam to hold it in place. You might try a different type of air filter element like the K&N that fits in the stock housing, or some kind of baffle up stream of the air filter element that forces the air stream to reverse direction or interferes with the path of the sound waves in some manner. I don't know enough about acoustics to suggest anything specific.

John Crawford
Click to expand...

Thanks very much for your input.

You describe that you don't hear the whine very much with the window up. What exhaust are you running? Do you still have the OEM airbox? Very interesting. So I think as you suggest that most of the noise can be damped down quite good. It has been 20 years ago but I still recall the basic physics of loudspeakers and dampening is very important there too. Another option for dampening material in the airbox would be to create a Helmholz resonator within the airbox which is very effective in dampening high and smallband-frequency sound pressure. Luckily the noise is mid/high frequency which is easier to damp than low frequency noise.

Thanks.
 

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