Reduce cabin noise: Different exhaust system? (1 Viewer)

[bikemaniac]

Hi,

I own a Toyota Hiace diesel from 1984. Its the one with the engine (2L) below the drivers seat. There is no wall between the drivers area and the rear compartment so it is one large compartment. The entire rear floor is covered with a 2-3 mm mat of bitumen to reduce noise. The engine is also insulated with some type of foam/fibre.

When I drive at 110 km/h it is quite loud. When I let the engine idle at 110 km/h the noise is almost gone - I only notice a bit of wind noise and a bit of tire noise. When I engage the engine again the noise is back again. To me it feels like the noise is not coming from the engine just underneath but from the large volume of space in the back. This is why I conclude that the exhaust system traveling the entire length of the compartment underneath is causing the excessive noise. But maybe I am wrong??

The exhaust system only has one cylindrical stock muffler in the middle at the moment.

Does anyone have information on how to reduce the noise? Will a different exhaust system help or is it a wate of money? Due to the construction of the van there is a lot of space for fitting more mufflers underneath and even larger muffler. Or will bitumen mats on the walls help more? It would be sad to invest money in noise reduction if it has no effect :-(. Anyone with practical experience?

I find it generally difficult to find information on exhaust system because everybody wants MORE sound from their system ... and I want less.

Lucas

 

[Dougal]

Silencing a non turbo diesel is basically the same as silencing a petrol engine.

It's a complicated subject but I have had good success in one of my vehicles by fitting a glasspack muffler in the middle of the pipe to stop resonance and a chambered muffler at the end. This vehicle is turbocharged though so that acts as another muffler (until the wastegate opens). I can't hear the exhaust while driving this vehicle and it's a 2.5"

But keep in mind there are many differences between an engine under full noise and an idling engine. Everything will make more noise at higher rpm and you'll get more vibration transmitted through the engine mounts too.

I owned a van once that was extremely quiet. It had about 20mm of heavy chip foam rubber across the entire floor with carpet over that. I think you would need similar in your van.

 

[bikemaniac]

My observations so far:

1 I tried to put a 15mm wooden board covering the entire floor of the van to dampen the noise. It did not help.
2 When I let the engine idle at highway speed (clutch pressed) - the noise goes back noticeable.
3 When I rev the engine in neutral gear at highway speed the noise goes back only somewhat.

So my conclusion so far is, that my large "box" ... the large volume of air in a fairly thin shell made of sheet metal and glass acts like a large loudspeaker/resonator.

Can I conclude that the worlds best muffler etc will not help because I continue to have my large air filled "box" in the rear? Or explained differently: If I install the best muffler dampening system, the noise will be reduced but barely noticeable?

Lucas

 

[Dougal]

You need sound absorbing material in the van. That wooden board would be a good start with foam both above and below it.

 

[mudgudgeon]

Also add something like dynamat to as many of the large flat body panels to stop resonance in the panels.
Eg roof, sides, inside doors, rear door.
Also some 10mm closed cell foam over the floor above the engine and trans will absorb more noise, also on wheel tubs to absorb road noise

 

[mudgudgeon]

If you can insulate as many surfaces as possible, then even closing gaps such as around gear shifter with closed cell foam can make a big difference

 

[gerg]

I second the closing gaps and dynamat. Least technically diffcult and most cost effective way to deal with it. Engine noise is not just from the exhaust. My engine makes very little exhaust noise yet is crazy loud in the engine bay just from fans and belts and injection pump clacking. Fortuanately for you high frequency noise is the easiest to insulate. My first cruiser ever... ahh I remember it fondly every curve and rust hole in the exhaust, no carpet and 2 barrell holly with the rat trap air cleaner on top... right down to the ear plugs I had to wear when I drove it on the highway. Very loud truck.