In my own case, I've been building and tuning high performance cars of all makes for roughly 25 years....So in general, comparing 2 motors of the same displacement and powerband, the only difference being 100 pounds or more mass due the BB/SB configuration, the one with the lighter internals will accelerate quicker due to the lighter rotational mass, not only in the crank/pistons/rods/ but also in the much lighter valvetrain. As far as cornering and braking, one could argue that 100 pounds of heavier motor would be similar to comparing for instance, the difference between a 235 pound driver to a 135 pound driver in the same car. In the end a car's handling is determined in large part by how well the static weight is distributed in the chassis and it's effect on the cars roll center during cornering and its instant (dynamic) center during acceleration. Bear in mind that every component comes into play, the driver, the battery placement, the transmission and also 50/50 is not always ideal sometimes a slight front or rear bias is preferable to a particular powerband, race course or driver preference. So there is no "right" answer...but, if then you consider the TOTAL weight, the overall lighter car (again all else being equal) is going to be faster and brake/handle better.
But with Cobra's and corvettes, a big inch small block can really make for an easy to set up chassis.....a 475-500 hp 400+ inch windsor can weigh the same or less than an all iron 289....another thing that comes into play is whether or not a scattershield is employed (highly recommended in a Cobra due to driver's proximity to the flywheel), a steel scattershield adds/concentrates about 45 pounds right near the center of the car and in a smallblock that centers the weight of the motor/transmission assembly (dynamically) back another couple inches, it can have a positive effect on the cars handling as well as add a tremendous safety factor. A big block can be very well set up, but to really get the weight down comparable to a small block is very expensive, especially when building an FE. Ironically FE Iron heads aren't that heavy (compared to many other big blocks) to begin with, but the block and rotating assembly is pretty heavy for 427" as is most big inch 60's motors. a 393-427" Smallblock Windsor can have a bobweight lighter than a factory 327 chevy...nice power in a lightweight package.
The "problem" when comparing Cobra combinations is that they are all set up differently...A well set up big block can run rings around a poorly set small block, no doubt...but that's not really appls to apples and I would say that the smallbock Cobra would likely be "inherently" better balanced "out of the box". The beauty of Cobras is that they can be and are all "seasoned to taste"; I personally tend to prefer the big block like torque over the high winding revs...but I prefer the light on it's feet (scales?) and predictable balanced feel of a lightweight smallblock powertrain in a 90" wheelbase car that puts a lot of rubber contact on the road. Again, it's about power to weight....apples to apples for the same power, lighter weight is generably preferable for handling, braking and acceleration.
Wize
www.fastraces.org (technical director)
www.streetwizeperformance.com