Okies, on Sunday I put the top airbox pipe back in to my Z16XE MK4. I left the bottom pipe out and am still running the Vectra intake pipe.
Darn me if the engine isn't transformed, smoother and faster throttle response, improved low rev 'power' and coming off the throttle is much smoother too. I will try it a few times further, but my test hill (Greenhead Bank for those who know the area) usually sees my car top out in 5th at a shade under 80mph (road closed for private testing yada yada) yet today it was (for the first time ever) creeping up and above this. It has never managed this in the 142,000 miles I've owned it...
So, curiousity has the better of me - for those that have done the 'airbox de-restriction' mod, put your top airbox pipe back in and see if you notice any difference?
Answer the poll and pass any comments in this thread - the pipe is the easiest one to get to as you only need to take the top off the airbox, so not difficult or time consuming to put back in for a while.