On my '95 Volvo 850 Turbo Sedan I notice that acceleration is great, but off the line if I punch it, it seems sluggish until the turbo kicks in and then it pushes me back hard. Is the turbo supposed to come instantly when I punch the go-pedal? Next time I drive I'll see exactly what RPM the turbo kicks in. I remember driving it when my folks owned it when it was brand new and it seemed to have more pep. Also we did change the stock 205/55 Z-rated rubber to 205/60 Bridgestone Potenza RE910's, T-rated blah :( because we needed an all-season performance tire. The car has 39k miles. Would replacing the stock air intake filter with a K&N give me back that power I seemed to have lost? Anything else I should get checked? My folks drove it conservatively for most of the car's life in Economy mode... of course I drive more aggressive and mainly in Sport mode. Will it take some time for the computer to adjust to my driving habits? The car has been drinking midgrade 89 octane, which may explain the loss of low end performance. I'm going to start filling it up with premium 91 or 92 and see what happens. Any other ideas are most welcome!

Thanks!