Thanks for taking the time to post your st2 parts..neat stuff to look at....Maybe this information can help
There is more than enough valve in a Triumph for most applications. In the 650 format there is too much valve and port to keep the airspeed up. (stock limiting port velocity is 520feet per second in the intake port which is too low. 620 is my personal goal and others have reached mach 0.6 resulting in over 650fps and super fast intake ports) For the folks here that speed the language the choking rpm of a stock T120 head is just under 7800 rpm which is too high for any stock crankshaft and stock rod/piston to stay together longer than a 1/4 mile. Reducing the valve and port size will make lots more power
Reducing the valve sizes to match the bore diameter will get you a machine that "feels like it is 200cc" bigger and produce a solid 60hp at the rear wheel over the stock 34-44hp (depending on what day of the week and how well the beer was flowing at the factory)
Raising the intakes 1/8" is a ton of work and yielded only 3cfm @25" more than a well developed head in stock dimensions
Where I like to concentrate the work is in the combustion chamber. Replicating the 1986 HD Sportster 1100 head (same at Buell Thunderbolt and 2004-2006 HD sportster) allows a very low dome piston and wonderful burn characteristics improving power, efficiency and overall timing (31 deg max on 89 octane)
The valve size recipe follows all formats of racing and manufacturing today and can usually be found in machines like your ST2 - 2 valve engines only - 4 valvers cover your eyes:
Best intake valve diameter range is 52-53.5% of bore diameter - the lower the better and will be dependent on the efficiency of the combustion chamber (no squish..no good)
Best exhaust valve diameter 72-78% of the Intake valve - Depending on exhaust type - Open race pipe for peak rpm power 72% - Muffled exhaust because of neighbors 75-78% - Stock exhaust need not apply for this job
This means the following:
A 650 Triumph with a .5mm overbore will work best with intake and exhaust valves of 1.46" and 1.09" - Call your local valve maker for some custom pieces
A 750 Trumpet and the BSA 650 bored up 1.5mm (my favorite) Can use the stock intake valve of 1.59 and drop down in size on the exhaust to a 1.18" for a huge gain in overlap flow getting the volumetric efficiency over the 100% mark (cams and port/combustion work required) My current goal is 108 and shooting for 110% VE
The Triumph Engine with its stroke of 82mm and the limiting RPM of 7800 (4200fpm) is in my opinion and experience the absolute red zone for the crankshaft design. Throw a 90 deg crank in there and a really really great outrigger bearing kit and maybe you can reach for 4400fpm piston speed average but its a fractional power increase and not worth it (opinion) 4400fpm = 8178rpm = BOOM!
I suggest all the energy be spent on the crankshaft. It is the official weak link. We can buy excellent pistons, excellent rods and even trick valve-train parts. Cranks will kill...just like the drug that inherited its name.
4 Valvers - Here is the rub
There is more flow under the curve with 4 valves...but no more top end horsepower because you can not rev the engine higher than is safe. It is harder to install 4 tiny vales in the cylinder than to make the exhaust valve smaller and Whammy! Your on the back wheel showing off at the next Delta road ride.
HillBilly - I am curious about your ST2. My 900SS hits the 52/74% valve size window on the nose, but Ducati was known to play with valve dimensions in the middle of a production run to remedy a poorly flowing head casting. (The "big valve" bikes)
Your Ducati should have a bore of 94mm meaning it should have Intake/Exhaust valve sizes close to 49/37mm respectively. I am curious what you find
- Based on what I have tinkered with in the 900 ish ducati range your bike can safely run to 8000rpm and would make 80 wheel hp at that point. The power is in there with little modification. The machine will operate at a 95% efficiency range. The camshaft timing is off from the factory...don't ask me why...ask Bike Boy
Or maybe you already know all this. Thanks for humoring me anyway.