Quote:
|
Originally Posted by madmelon
No idea but I remember reading an article on the AFR Heads website about the 350 Chev "should have build"- a 0.125" larger bore and a slightly smaller stroke with the same or longer rod. It made very impressive power and it was able to use rather a high compression ratio.
Harmonics are a big problem in crankshafts but it's not the primary harmonic that does the most damage- it's usually the 3rd and 4th harmonics that cause fatigue failures due to their larger number of cycles (factors of 3 and 4 higher respectively). There area huge number of ways of attempting to balance and dampen this out, depending on the type of engine. The old radial aircraft engines are particularly interesting. It's a real challenge to engineers to try and eliminate radial and torsional harmonics without making the components stupidly complex or overy heavy (ie poor responsiveness), even with todays computer simulations available. |
I kind of agree with you, but don't underestimate first and second order harmonics/forces, especially when applied to an engine other than a six cylinder.
Simple harmonic motion doesn't generally occur in a combustion engine cylinder, because the piston travel isn't equal per crank radian travelled. The second harmonic is twice the cosine frequency of the first harmonic at an acceleration value equal to the rod length/half the stroke length (R/L). Because the second harmonic is exacly half the frequency of the primary, TDC forces are cummulative while BDC forces are subtractive. On a six there are sufficient counter forces to equal things out. On a four there is sufficient imbalance to cause some pretty nasty damage, third, fourth and nth order harmonics aside.