About rod strength (or weakness) in a N/A or Turbo'd engines, here is an excellent article written by Corky Bell of Bell Engineering Group, Inc & Cartech Mfg:
"The net result of hours of calculation revealed the outstanding picture that an engine's loading spectrum was composed of TWO independent forces; the inertia loads generated by piston accelerations up and down the bore, and the power loading of burning gasses pushing down on the piston, creating power. A summary of the calculations revealed the following interesting points:
1) Inertia loads just to turn the engine at the readline are HUGE.
2) Power loads are so small by comparison that they are relatively insingificant.
3) A typical engine will have almost FOUR TIMES greater compressive inertia load at its Bottom Dead Center (BDC) crank position than the maximum power induced compressive loading from fuel ignition just at or before Top Dead Center (TDC).
4) An engine will fail a conrod ONLY at Top Dead Center (TDC) on the exhaust stroke, when inertia causes tension (rod stretch). At this point, there is no offset to the inertia load from power loading whatsoever (allowing the rod to snap).
5) An engine designer will be interested in two loads: the inertia load at Top Dead Center (TDC) and the inertia load at Bottom Dead Center (BDC). POWER IS OF NO CONCERN!
6) Power loading does NOT become significant, relative to the inertia loads, until the original power is increased by a factor of approximately four.
7) Inertia loads increase with the square of the RPM......NEVER EVER, over rev an engine.
8) At the time of the engine cycle when the power loads are the highest in compression, the inertia loads are very high in tension. Interestingly, these two loads SUBSTRACT in absolute magnitude, one in tension and the other in compression.
Since the inertia load is FAR higher, the opposing power load only tends to REDUCE the sum of the two loads. Increase the power load (higher compression, supercharging or turbocharging) and you will observe the very interesting result of substracting a bigger piece from the dominant inertia load at TDC, thereby reducing the overall load in the conrod, REDUCING rod stretch (tension).
The argument Summed to this: when increasing the power output of an internal combustion engine, keep the RPM at a reasonable limit and INCREASE the combustion pressures to almost anything and the net result will be little increase in the structural loading of the engines internal components (generally the rods = weakest link). Basically, power loading will NOT even tickle an engines internals."
Any Questions??? (maybe I shouldn't ask!). Rustie............
