Hey Everyone! I found this by doing a search and was so excited, decided to become a new member of your club, as I might be able to provide a good answer for the question posed in this thread!
I've had 3 VW Beetles and my dad had a few Porsches (356/911) when I was a kid, plus he taught auto/metal shop at the local high school here in Anchorage. My last Beetle was a 74 Super 1600. I put a CW crank in and polished the manifolds/heads and that alone made a huge improvement. Also had a severely mismatched Starion 2.6L turbo that I scabbed on... It wouldn't kick in until high RPM's, but it accellerated so fast that it snapped the fan belt every time! My '66 beetle weighed < 1200 pounds when stripped down, so 1900 is a bit high if you consider carbon/glass fenders hood, no bumpers/spare tire/rear seat.
That all said, here's my take on why the beetle could beat the bike:
1. Ferdinand Porsche was a mechanical genius
. He won "Engineer of the Century" for the design of.... that's right, the Beetle
2. Air cooling
shaves hundreds of pounds of weight off the car- no radiator, fluid, hoses, water jackets etc.
3. The arch
! The Beetle is one big 3 dimensional arch... This makes it much stiffer than boxlike cars. That translates to higher torsional rigidity resulting is virtually no wheel hop/chatter. This along with air cooling are the main reasons the beetle is so light. Compare this to a body on frame in terms of rigidity and weight.
4. All power transmission is routed through as short of a distance
as possible. There is no driveshaft, and in the old beetles, not a single u-joint, as that is built into the differential, which is built into the transmission(actually transaxle). Compare that to a front/rear layout with the tranny/u-joint/driveshaft/u-joint/differential. Each step you have to deal with torque and vibration, increasing mass all along the way. The increased mass of rotation equates to significant inertial losses 1/2MR^2 not to mention the increased weight of the vehicle.
5. Rear engine, rear wheel drive
. Think beyond the 60/40 weight distribution to a dynamic situation where you pop the clutch. First thing that happens is the front of the vehicle lifts up. Second thing is the rear of the car squats down on the springs, coupling 100% of the car's weight to the rear wheels through the rubber bumper/trailing arm. Think of it as a huge lever with the rear wheels as the fulcrum. Without wicked traction, power above what the wheels can handle is simply wasted.
6. Trailing arm rear suspension
. (bikes have this too) Compared to a leaf spring/straight axle suspension, the force transfer from the rear wheel bearings to the vehicle is much more direct. The torque/inertia reaction makes the vehicle squat.
7. The rest is the misconception that the original flat-four beetle engine was a dog because of it's basic layout... no, it was due to it's intentionally very small carburetor/manifold
. Remember, it was developed in the 30's when the US had cut off Germany and Japan from petroleum. Fuel in Germany then was at a premium (Battle of the Bulge decisive factor?). It doesn't take much at all to turn a 1.6L bug engine into a screamer. Bore it out, add a turbo/EFI/racing heads/lifters/cams/rods/pushrods/rockers/100 octane and you can get a power/weight ratio double that of your bike. Here's the math- bug 1200 pounds/400 hp bike 450 pounds 84 hp. So the bug has 0.333 hp/lb and the bike 0.18 hp/pound- bug having double the power/weight
as the bike.
Here's one of my favorites of a VW Bus of all things dusting a Mercedes C32 V8- how can this be?
Besides the above factors, consider the Mercedes is front engine/rear wheel drive now with the added burden of traction control, which essentially limits the engine's power if the wheels can't use it. Not sure what engine the C32 had in it, but it's still cool to watch. Notice how the bus just squats and squeals all through first and chirps in second.