I got 5 x 1.5cm holes on the front of the bottom half of the box.
Adds a wee bit of induction noise... not loads, enuff to sound nice.
Too many holes will boom and create a lot more noise
I did this when i put my K&N panel filter in, did feel a wee diff which i reckon was a combo of the filter and holes.
I remember looking at a Max Power type mag and they'd done testing with a nova using diff cone filters/panel filters, holes/no holes all on a rolling road. At the end of it all they found out the system with a K&N panel and 6/7 x 1cm holes was the best result. Obviously diff cars will differ.
I used this as a guideline, and used bigger holes as the car is higher power and bigger engine.
any help at all?