Lnewqban - "Vision without action is a daydream. Action without vision is a nightmare." - Japanese proverb

No wonder it seems like ever thing is a nightmare....my vision is not so good...but getting a little better!

I would say that exhaust with a 25mm inlet & outlet should work fine. When gasses cool they take up less space...hence some exhaust systemshave a lot smaller outlet. The guy should give it a try anyway....unless he lives in a hot dessert area. Capt,n