I don't know what chassis you tested but I tested my Berrien chassis much the same way you described and the torsional rigidity was 15% stiffer on the Berrien chassis and it is 10lbs lighter then the shortened VW floorpan. Other benefits include the fact that I don't have to worry about the fuel line leaking in the tunnel or the clutch cable tube breaking loose in the tunnel.
I did the testing 2 years ago to quiet some friends of mine.
Still there is nothing wrong with using V Dub pan they do a fine job.
: Recently, I've been in several conversations regarding which is
: better to use with a F/G DuneBuggy body, a shortened VW pan or a
: custom tube frame like the one offered by Berrien & others.
: I've heard & read about a test, that the Australian
: government makes the fellow who is the authorized builder of
: Manx's down-under & any kit car builder, put their
: Buggys/kitcar thru, before they OK them for manufacture &
: use, especially shortened VW pans. The Australian government
: engineer's test, requires that the stock length VW floorpan with
: the stock VW sedan body attached, is bolted rigidly to the
: concrete floor at the 2 outer ends of the rear torsion bar
: housing & at only one outer end of the front torsion beam. A
: bottle jack atop a scale is placed under the one remaining
: unsupported corner of the car & the jack is pumped up until
: the scale reads 250 lbs. & a measurement noting the
: structural flexibility or torsional movement in the cars overall
: structure is taken & recorded. Next, the body is removed
: from the floorpan & the same test is conducted & the
: measurements recorded. Surprisingly, there is only a small
: increase in the pan's torsional softness. The body structure,
: likened to a bridge, no doubt adds greater beam strength front
: to rear, but it does very little to resist torsional twisting.
: The VW floorpan's centerline cylindrically shaped tunnel,
: provides most of the torsional resistance. Next, they perform
: the same test on a shortened VW floorpan & it proves to be
: even more torsionally rigid than the stock, full length pan with
: the body attached! Of course it's stiffer, because it's shorter.
: We must understand that the VW floorpan's centerline tunnel, is
: a cylindrical form, simply put, a sheet metal sheer panel,
: stamped to form the upper half of a tube, afterwhich the bottom
: is welded on to complete the tube. Sheer panels, short of
: destruction, will not be forced to a parallogram, anymore than a
: cylindrical tube will twist torsionally. The VW floorpan, while
: it seems antiquated by modern standards, at 135 lbs. is still
: uniquely 65 to 75 lbs. lighter & torsionally stiffer than
: other aftermarket chassis advertised as "lighter &
: Now, what does all of this mean? Well, for my preference, I'll
: continue to use a shortened VW floorpan. While these new chassis
: are intriguing & I'm sure there is a market for them, I'll
: stay with the "old way"! What do you guys think? Have