Currently making an airbox to hopefully sort out some of the noise related problems I get at certain trackday venues. Basically the box is going to be of aluminium construction, fixed on where the normal pipercross sausage foam filter usually attaches and have a cone filter on the front of it. All of this will be sticking out of the bonnet.

I have found a couple of possible cone filters to use the question is which one (see below). I think the one with the hole in the top (right one) may force more air into the box causing the engine to run lean (running on blackbird carbs).

What are people's thoughts ?
Rescued attachment whichfilter.JPG

I suspect the noise will not be abaht by just moving the filter alone and sticking it outside the bonnet.

To kill the noise you really need to place the filter inside a box then have a couple of baffles from this to the outside world.

Noise does not like bends so you do not need to impede airflow with the baffles, just use a big box with baffles that effectively stop you seeing the filter a couple of times.

Also placing the intake immediately infront of the rad but still inside the confines of the bodywork is a good way of killing the noise.

At a first stab I would be inclined to duct to the front of the car in 3" pipe and stick a filter on this, a couple of 90 degree silicon bends and some ali tube should do the trick, convulated tube is not good.


Regards Mark

I use those on my XR4x4 and they seem pretty good to me. Done 12,000 miles and no problems yet, cost about £15-£20 charlie browns etc.

Thanks, Mark

My thinking is that the foam filter already sticks out of the bonnet and at a recent track day gaffer taping cardboard over it lost me about 4dB on the drive by meter. The airbox is more an effort to direct the noise away from coming out of the side of the car (towards the noise meter) and projecting it forwards. Without making major modifications I don't have the option of ducting the air from the radiator area. This is just a clip it on for the track / take it off afterwards solution (it will probably look ridiculous anyway).

[Edited on 6/10/06 by givemethebighammer]