Yipe! Those stock cam specs (both of 'em) are really weak!
For those of you who think metric measurements are a French (spit) Commie plot, the lift translates to .374" IN and .370" EX. At first blush, this seems short, but remember that this is a 4 valve per cyl. head, and they can get away with shorter lift.
And, yes, the shorter ex. duration is to help with smog reduction.
The duration figuers of 242* IN and 216* EX are probably "design" duration. On solid lifter type cams (as opposed to hydraulic cams), this duration is usually measured at .006" lift. This makes that small cam seem larger, but, the first few degrees of stock cam lifter movement is a slow rate, so that the valve lash can be taken up before the faster movement is applied to the lifter. This helps keep the valve train pounding to a minimum.
The slow lift rate lowers valve opening speed, so the cylinders don't get a chance to fill very well; read, lower horsepower.
CAM SELECTION TIP: The Bonny twins translate to around a 2400 cc V-6 car engine. Go to your favortie cam grinder's catalog to see what grinds he offers for V-6, 4 valve engines. Crane, Comp Cams, Isky, or others, will have their basic street grinds listed. ANY mild cam they do would make a decent choice for recamming a Triumph twin, I should think. Look for solid lifter grinds, but a hydraulic grind would be fairly close.
There's lots more to this, but it's 2 am after a rather big Thanksgiving day and I'm pooped out. Beddy-bye time for Grandpa.
