Main cap girdles re-discussed

DNasty777 said
I'm of the mind to agree with you generally, about the main girdles. From what I've read so far, most of the complaints seem to come from the fact the girdle isn't really tied to the caps at all, just sandwiched on top of them by the studs. I'd be inclined to believe that if the girdle was keyed to each of the caps, or the caps and girdle were one piece like a 4g63 or other import motors that I've seen, that would improve rigidity greatly.

If you watch the David Vizard video you will get the information you need. Now his explanation was concerning the SBF engines breaking the main web out of the block. With his extensive list of industry contacts, he talked to a Ford engineer who informed him that the caps under high power and RPM would resonate front to rear. When you get to a resonante frequency that matches the natural frequency of the block or multiples of it they will break the block. The solution is to change the natural frequency. You do this by changing the mass of the part or the length or clamping it. What a main girdle does is clamp caps together, effectively changing their mass.
I was exposed to this while working in a facility building oilfield compressor packages. On some units a company was contracted to come in and measure the natural frequency ot the piping and vessels. That frequency was compared to multiples of the engines designed full load RPM. If the engine operating RPM is 1300, then a natural frequency of 650, 2600, 3900 etc were to be avoided. Sometimes just building a pipe out of the next gauge heavier or larger diameter would change it enough. Sometimes a sleeve could be welded on the outside in the center of a length of pipe did the trick. This was not the best.
You have probably seen vehicles with a weight bolted to the transmission tail housing. That is what it is for, to change the natural frequency away from the driveshaft RPM frequencies. Same principles and physics involved.