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Something occurred to me the other night when I was working on my dad's car... it didn't have a flap on the air filter box! My old tubby estate had a spring-loaded metal outwards-opening flap in the top of the front-facing part of the box, presumably to dump excess air out when the dump valve opens.

I've checked servicebox and there's only the two boxes in use - one for dusty climates (ie, non-uk) and one for non-dusty, and I'm moderately confident that would just change the filter installed in each one...

So what do other tubby owners have?

I'm pretty sure mine hasn't got it, I'll have a check later Matt.

I'm trying to think what the air release valve is for - I don't think it's to relieve dump valve air cos there's not realy enough volume on a LPT; and you'd kinda hear something going on there. Maybe it's to relieve ram-air pressure? there could have been problems on the higher speed models of the incoming air scoop popping off at speed? the release valve would equal out the pressure.

Discuss........