I should add also that just because the sled is ported does not mean its gonna be a gas hog, the trail porting I do runs stock 2001 srx mains/jetting, this is with ported cylinders, machined heads and piston mods. I like the use of the 42.5 pilot jet, stock 3rd groove needle clip with both washers under the clip, stock 2001 mains.
Something most people dont think about is clutching and gas mpg go hand in hand with each other, if you have a lousy inefficent clutch set up, your sled is eating up fuel because your wasting the energy to be transferred to the track. Rolling resistance also plays a roll in gas mpg, dragging the track at the curve, too tight of a track tension, the addition of oversize wheels all play a role in gas mpg as well.
Tempa Blows have thier place on the touring sleds or something non hi performance like the old twins or a venture or something, but when they are added to a hi performance piped machine, you usually spend more in piston replacement then you save in gas!