Don't waste your money on an after-market pipe for a 670. Bombardier didn't leave very much on the table in that area. The best is the 98~99 Summit X or 1999 MXz 670 HO pipe for all around useage. This is with the heavy "suitcase" muffler. Twin pipes tend to score pistons due to rapid heat build up. Take your replacement y-pipe and shorten it 13MM. Cut right behind the ball connection to the spring perches then relocate the perches 13MM back (to wards the jugs). Shorten the rotary valve cover 20MM and machine a new pair of spigot grooves in it. Taper the inlet side of the cover starting at 44MM going down to 42MM at the valve. Taper the tunnel ports from 42MM at the R/V surface to 50MM inside the crankcase. Use the 164 R/V plate (better accelleration) timed a @ 144 - 72 degrees instead of the 169 (optimized for oval ported twin pipe equipped 1994~95 Mach 1). Adjust combustion chamber volume to 19CC and set ignition timing to 2.18MM (.086") BTDC
Notch the rears of the cylinders like this.
640 x 480 (36.44k)
Open the tunnel entries like this
Carry the tunnels through to the cylinder notches like this and bevel the intake bowls 9MM and machine the cylinder intake ducts to match
Modify R/V cover like the R/H one
Clean flow and polish the exhaust ports like this
Then run it on 91 RON & MON octane fuel and you should be good for a reliable 130 HP... did I miss anything?[/b]
I've been on google for weeks and this is the best advise I've seen on the net, by far!!! This should be pinned at the top of the skidoo subtopic!!!