Learning Info: Just a quick note on the proper installtion of the HP Exhaust from Riva: Make sure before you slide the WaterBox end on the header pipe end to Positon the 2 rings on the header pipe end and paper tape them into place before you try to slide the header pipe end onto the WaterBox end: If these 2 rings are not installed properly the result will be a hole burned through the coupler best to have a Shop Manual that shows how to properly install these 2 pieces. The rings look just like piston rings and they have to be installed properly or the WaterBox end will not slide all the way up to where it needs to be to prevent exhaust form leaking and burning the coupler...I will let you know how well it runs without the hole in the coupler, it only ran 61.5 with the hole in the coupler, not bad for a ski trying to comitt suiside....