Got these to go on the webers as I needed a quick and cheap fix. £25 off the manufacturer on eBay, they come with 2 holes to go over the inlet trumpets. That meant I had to create 6 additional holes in the base of the filter. 2 for the jet tubes and 4 for the bolts which stick up at each corner of the trumpets. I used a calibrated bic pen and my index finger to make these holes and they worked perfectly. I can testify that the foam is mega tough and I can't see that I'll have issues with it degrading and breaking down to the point where they get sucked into the carbs. I haven't run them on an engine yet so can't testify as to how they perform in terms of preventing nasties getting sucked up but I think they'll be pretty good. I was recommended these by my RR guy who builds F3 cars and other exotic race cars and he says that without external damage they'll see through a race season and can be carried over, he sells his used ones on, so that's good enough for me. Only issue I can envisage is that they'll be hellish noisy
