Seems like we’re digging up the old discussion from several years ago regarding how flywheel mass affects HP and torque of an engine.
http://www.accessnorton.com/heavy-flywheel-equals-more-torque-t19324.html?hilit=al otment
I believe the tangent we’re presently running on (variations in crankshaft angular velocity during a single Otto cycle) started with mdt-son simplifying his explanation, at Eddie’s request, where he stated that relative to a heavy flywheel engine “the light flywheel engine will…..
1. speed up and decelerate the crankshaft faster (angular velocity),
2. less engine torque is used on speeding up the flywheel,
3. more torque will be available at the PTO as long as the engine speeds up and less as it decelerates, and
4. Provided the resolution and accuracy is good, the Dyno will show a higher torque and power during acceleration and less under deceleration of the crankshaft, if all other parameteres remain constant.”
I’m quite certain that mdt-son’s 4th point simply referred to a full rip on a dyno and what occurs on the acceleration trip up and the coast down after the throttle is chopped. However some here have dissected the statement from this macro intent to the micro and are now examining angular velocity of a crankshaft over a single Otto cycle. We all know that significant variations in crankshaft velocity and torque occur during a single Otto cycle, so what is it that we are trying to unearth via this discussion of minutia?
The paper “Determination of The Engine Torque of a Four Cylinder Four Stroke Diesel Engine on the Basis of Harmonic Analysis of the Crankshaft's Angular Velocity” provided the following graphic illustrating variations in crankshaft angular velocity and torque that occur during a single Otto cycle. As the graphic clearly shows, the crankshaft velocity and torque vary significantly during a single Otto cycle. The authors attribute the higher range oscillations occurring in the measured velocity trace to elastic deformation of the crankshaft.
Our Norton engines will likewise have unique signatures of crankshaft angular velocity and torque that will depend on the given engine configuration.
In light of the above perhaps we can quit pissing in the ditch and get back on the road to constructive conversation. And with that, I’ll throw another target up on the road to get our focus off that target down in the ditch.
We’ve discussed much about heavy and light flywheels and how they affect HP, torque and dyno results, and IMHO have stated the large majority of the outcomes correctly. So here’s another one for the experimentalists in the crowd to try. It really makes no difference whether it is a heavy flywheel or a heavy rear wheel that adds mass to the system since any component subject to angular acceleration (shafts, gears, hubs, rims, etc) affects the system in the same way. So here’s your experiment, fit a water tire (filled with water instead of air) rather than an air tire on the rear of the bike and see how that affects the general feel of the bike. It’s a common thing, where allowed, in amateur flat track racing but you better be ready to chop the throttle in the vicinity of the starting line or you’ll be off corner #1 somewhere out in the weeds as the added wheel mass keeps right on flywheeling you along. Of course the benefit of the heavy wheel is that coming out of a corner the extra mass makes it more difficult to accelerate and break loose (better feel for the track) and the extra weight improves the tire contact patch on the track surface. A feather weight wheel/tire combo might be 12-15 lb and a water tire might be in the vicinity of 40-50 lb, so huge difference, especially with the extra mass positioned at such a large radius. While you’re doing that I’ll start generating that crankshaft torque/velocity plot for the air tire and water tire. Results should be absolutely titillating. Stay tuned I should have that wrapped up sometime in early 2019.
