Air intake quieter

[crt]

Hi,

I'm having trouble with the noise my car makes. I'm only allowed 95db.
And i am getting 97db. Last time i refilled my silencers but i didn't help enough.
Now i'll be trying to get the intake a bit quieter.
I'm running throthle bodies with airbox on 2l 16v engine. The air filter is a conical K&N filter with inlet diameter 11cm.
What could i change to make a difference?

Greetz

[Al Weyman]

If they are testing the car static at the track i.e. standing still and revving the thing I doubt it will make hardly any difference as you will only be on a fraction of the throttle, if however (and this is a major bug bear of mine as I know cars far noisier than my V8 on the track) its a drive by then yes it will make a hell of a difference. Maybe an airbox is the answer?

[crt]

I have an airbox witch goes to the K&N filter.
Here at Zolder there are two points were they measure.
And this is at full load on the track.

[JohnD]

crt,
Front engine?
Then the air box would need to be a lot noisier than the exhaust to make a difference. Noise follows the inverse-square law, and sound level drops by about 6dB for every doubling of the distance from the source.
Sound testing is usually half a meter from the exhaust, so a front engine, three meters away (?) would need to be about 18dB louder than the exhaust at the pipe!
In your case, 115dB!

An expansion box before the main silencers might help. No filling, just a resonance chamber.

JOhn

[Al Weyman]

John I think he already intimated he was subject to driveby testing so I don't think that theory holds water, I remember a de-turboed Cossie I used to race against on throttle bodies and you could hear the thing coming towards you from the far side of the circuit as its screamed like a banshee and was most unpleasant just the sort of noise that gets circuits shut down, as soon as it went past silence! And yet it was my far quieter V8 that was usually picked on by the static sound testers because we did not have drive by testing back then which IMHO is much fairer.

Here at Zolder there are two points were they measure.
And this is at full load on the track.

[crt]

The DB meter is at a distance of about 10 meters off the track and a height of 1.5meters. They measure it every time you pass.
The car is a front engine car.

[greenamex2]

Originally Posted by crt

Hi,

I'm having trouble with the noise my car makes. I'm only allowed 95db.
And i am getting 97db. Last time i refilled my silencers but i didn't help enough.
Now i'll be trying to get the intake a bit quieter.
I'm running throthle bodies with airbox on 2l 16v engine. The air filter is a conical K&N filter with inlet diameter 11cm.
What could i change to make a difference?

Greetz

Is it a Vauxhall XE engine?

[crt]

Originally Posted by Denis Bassom

Is it a Vauxhall XE engine?

Yes

[greenamex2]

Spooky.

These are renowned for being 'noisy' engines, especially on the intake side when fitted with throttle bodies.

I had one in my kit car and ended up knocking 5-10BHP off in order to get it under the typical 'noisy' drive by track day limits.

Got a picture of your installation you can post?

[MGDavid]

crt, I fell foul of similar noise test at Zandvoort - we found out which side of the circuit the test equipment was (infield) and so we welded a short 90 degree curved pipe on the end of the tailpipe to point towards the outfield, no more problems

[crt]

Originally Posted by MGDavid

crt, I fell foul of similar noise test at Zandvoort - we found out which side of the circuit the test equipment was (infield) and so we welded a short 90 degree curved pipe on the end of the tailpipe to point towards the outfield, no more problems

In Zolder there is one on the right side and another on the left side.
I tried a bend down on the exhaust but no luck.

[crt]

Originally Posted by Denis Bassom

Spooky.

These are renowned for being 'noisy' engines, especially on the intake side when fitted with throttle bodies.

I had one in my kit car and ended up knocking 5-10BHP off in order to get it under the typical 'noisy' drive by track day limits.

Got a picture of your installation you can post?

Here is a picture.

[THR]

2 silencers? one facing out and one facing in? like v8's have!?
be quite trendy too lol

[R59]

Silencers in the exhaust won't cure the intake noise that crt is suffering. This is intake noise.

The Vauxhall XE engine really does bark when it's on cam. One idea may be some sound deadening material applied to your plenum chamber an intake tube. Some fireproof matting could do the trick.

It could be that the length of the tube is resonant and amplifying the noise.

Are the throttle bodies fitted with trumpets? Again, using a different length may change the point of resonance, and the noise level.

Another option would be to build a split airbox that feeds two smaller air filters - one left and one right - it looks like there's space for that.

Worst case scenario is that you need to change the inlet cam profile to something less aggressive.

It's quite likely that whatever you do to reduce the noise will affect the power output of your engine, other than fit a V8 in there.....

[JohnD]

Originally Posted by crt

Total side issue, crt, but why/how is that crossbrace to the suspension towers so bendy? Can it provide any stiffness?

And, Ah! So! Drive by meters!

Would a layer of soundproofing or anti-drumming material lining the bonnet help? Like posters above, I suspect that something is amplifying the noise by resonance.
Another simple experiment would be to mount the airfilter on the opposite side, with a much shorter intake duct, with the same object, to change the resonance.
A non-simple experiment would be to enclose the filter in as a large an airbox as you can, and supply it with air (that would be much colder than under bonnet air!) from a duct in the bonnet.

Good luck! Please let us know what works, or what doesn't work.
John

[greenamex2]

Originally Posted by JohnD

A non-simple experiment would be to enclose the filter in as a large an airbox as you can, and supply it with air (that would be much colder than under bonnet air!) from a duct in the bonnet.

Good luck! Please let us know what works, or what doesn't work.
John

That was what, essentially, we ended up doing on my kit car.

A more expensive but simpler option may be to get a 'remote filter' from Reverie.

You also try double layer ducting hose or, as someone else suggested, soundproofing the existing hosing.

[tristancliffe]

Originally Posted by JohnD

Total side issue, crt, but why/how is that crossbrace to the suspension towers so bendy? Can it provide any stiffness?

Nope. That brace does two things.

1. It adds weight
2. It provides a handy place to tie wrap other components.

Get rid of it. You'll go slightly faster with slightly better handling.

[JamesH]

Just because the brace is bent, doesn't mean it's bendy (it could be 5mm walled scaffold pole for all we know).

However, whether it makes any difference whether bending or not is up for grabs.

[crt]

The inside of the bonnet has already got soundproofing.
So if i do the complete airbox an intake tube, this would also help?
There are trumpets in the airbox. Feeding the air trough both sides of the box is a good idea. It will be a little work, but i'll tried this option last.
Tomorrow i'll tried fitting the filter straight to the airbox.
I was also playing with the idea off an intake resonator? Does anybody know about this? Or even tried it?

Thanks for all the good idea's

PS

That strutbar was on there wenn i bought the car. It is made from thick Alu tubing. The front of a kadett is not so strong, so every little reinforcement helps.

[Ted bennett]

Could you simplify the installation by removing the flexi hose which turns through 180 degrees and the length of drainpipe which may be acting like a didgery-doo. Park the filter in the space vacated by the removal of the 180 flexi and consider enclosing the filter in a box fed fresh air from somewhere handy like a bonnet vent. I figure the longer the duct between filter and airbox you have, then the greater the capability for noise generation.

Edit; A closer read of post #19 reveals you beat me to it.

[KAM]

well for a start the induction tubing is rather oversized. You could run a smaller tubing and filter for the power you are running. That might help any resonance.
But surely the most simple solution is a bigger silencer. Its not like this will reduce power....

[R59]

Originally Posted by tristancliffe

Nope. That brace does two things.

1. It adds weight
2. It provides a handy place to tie wrap other components.

Get rid of it. You'll go slightly faster with slightly better handling.

It actually does four things....

You had the first two...
3. Keeps the floppy strut tops apart on a GM Astra/Kadette
4. In the event of a shunt, transfers the impact from left to right/right to left, and thus wrecks both sides in one go.

Still stand my my comment - put a V8 in it.
You'll need to do a bit of welding though.....

[Chris Wilson]

What about putting the filter INSIDE the car? Depending on its construction it may well act as a further barrier between its intake resonances and the circuit noise microphones? You'd have to wear ear plugs... A friend made me a turbo engine plenum from an old fire extinguisher alloy casing, because thinner ones tend to crack and split with the pulsing. Conversely, a heavy cast plenum will dampen the noise of an N/A. I have an XE in a sports GT car, and I too feel that a lot of perceived noise is intake generated, albeit mine is on humble Webers.

In your case a cast alloy plenum, double walled tube with an expanding foam liner between the walls, and an in car filter in a lagged case maybe pulling air from under the car, may be things to consider. What a PITA it all is though.... Whilst i love the added spectacle noise brings to some sports it would be cool if F1 had to meet noise limits at some circuits, then those with the money and resources could develop this *hit and we could plagiarise it as best we could!