There are several issues here.
1/ Dynamic vs static.
Depending on who you talk to, dynamic either works in more than one plane, or dynamic means "working with the motor as a working whole", while static always means spinning the flywheel or other object on its own, usually by hand, to find the dead spot. Dynamic "usually" means, TO THE BALANCER HIMSELF, smoothing out the motor over its operating rev range, whereas Lister CS was not an engine built to run up and down the rev range.
2/ What are you trying to balance?
here is where shortcuts get taken, and people do what is easiest, and don't do what is harder or what they can't figure out how to do.
Balancing and engine, complete, that is not running under it's own power but is being spun by an electric motor is wrong, because we are talking about engines with big impulses of torque at low frequency, one stroke every tenth of a second, two tenths just pumping free gas through open valves, then one tenth compressing then one tenth power in the opposite vector, then two tenths idling again.
In this sense "30% dynamic balance" was often used to mean "balanced at 30% of rated horsepower", so about 2 bhp on a 6/1.
You have purely rotating parts, crankshaft and big ends, *theoretically* purely linear parts, piston, THEORETICALLY because 100% of engine torque (action and reaction) is thrown against the barrel, where do you think ovality comes from, and complex gyrations, the con rod and in reality to a lesser extent the piston assembly.
the old fashioned rules were right, vibration is a function of the relative magnitudes of the actual forces developed inside the engine, to the total rotating mass (not eccentric mass) of the flywheels... with 3,000 lbs of flywheel per side a Lister CS 6/1 at 650 rpm will feel like an electric motor..... my original s-o-m with 300 lbs per side will run smoothly down to around 55 rpm, at which point there is no significant torque / time impulses to make it vibe, esp flywheel mass / (torque / time) point of view.
so..................
a/ you need to up your flywheel mass, 300 lbs a side minimum, the extra weight does not need to be eccentric, just weight.
b/ you need to up your gen head flywheel mass, another 150 lbs minimum.
c/ you then need to run it under load, drawing 1.5Kw per 6 bhp rating, and balance it as smooth as you can, so it will vibe more at zero load and at full load, but mainly you'll be at or near the sweet spot, because few will run at zero load or full load all day.
how much is too much?
In terms of wind resistance losses and bearing losses, 3000 lbs is probably the point of diminishing returns for flywheel mass for a 6/1.... remember, constant RPM engine, so lack of throttle response as required in a vehicle ain't an issue, we aren't waiting for the revs to drop to engage the next gear.
