air box's

[judgie]

its running a 400mm long x150 dia 2.5" bore straight through box. problem i have is the sound meter is help .5m from the tail pipe so the meter is picking up all the background engine sound as well. striaght cut cam gears, porsche fan and the intake roar. hence why i'm moving the exhaust exit to in front of the rear wheel, gets the sound meter further away from the engine so hopefully should make a bit of a differance.

[evilC]

Hi Rob,
I understand the problem as I had a similar one on my Imp road rally car that was marginally over. I used to solve that one in one of two ways 1) reset the tacho so that the revs always read higher than the test limit i.e. at the 5k rpm test point on the tacho the engine was only revving to 4.5k rpm and 2) To always stand over the test point that added some absorption that was usually worth 2dBA.
I think Steve's idea of sound insulation under the deck lid is valid, although weight inducing.
On airbox volumes I thought that the airbox should be 1.5x the swept volume served but I will be corrected on that one. As intake noise will be adding to the woes it would be well worth insulating the airboxes and the connecting pipework that will reduce noise and air temp absorption. Also, it would be worth considering the direction of flow and creating as smooth a flow as possible (pipes dumping into a can ontop of the carbs ought not to flow properly). Air filters can help in reducing noise and smoothing out the flow if you haven't got them already.

Clive