Spark plug BERU or OEM Honda

And timing belt, and spark plug change every 90 K miles or so.

Sounds like it could be a spark plug. For some reason the Prelude likes to eat through them. Shows the exact same symptoms you describe (loss of power, different exhaust note).

I've had much success with BERU plugs on all of my VW's, especially my 16V's. Beru maks the stock/replacement plugs for Porsche, VW and Audi (I work at a Porsche dealership, I see it all the time)

I use Beru Utra-X UXF79 4 tips plugs. It's a great plug for my chipped B6.

I would call New Dimensions... but I decided to go with the Beru Ultra-X. These have 4 nodes instead of just 1 on the head of the spark plug. They are awesome!

Beru Silverstone all the way....Spendy, but worth it, totally. I have taken the pplugs out a couple of times since I put them in a little more than a year ago, and have found very clean plugs, no fouling at all. the electrodes were in the same shape as when I bought them, hardly worn down at all.

i've had the beru ultra x's in for about 8K...no problems...no noticeable improvement either...starts the same (good), runs smooth...no complaints, but no better than stock...