FredSVT and All:
I LOVE what all you say. YOU are one of the guys who needs to be "in charge" of Detroit. Clean house, get a clean sheet of paper, and start FRESH.
Back on topic...as to pushrod-actuated valvetrains versus OHC setups.
Fred, I am going to "bust your chops," just a little bit...but in a nice way, hoping you take NO offense to what I say:
Some specific problems that remain with pushrod engines:
Limited engine speeds...as in RPM - Pushrod engines have more valvetrain moving parts thus more valvetrain inertia and mass. As a result, they suffer more easily from valve "float" and may exhibit a tendency for the pushrods, if improperly designed, to flex or snap at high engine speeds. Therefore, pushrod engine designs cannot revolve ("rev") at engine speeds as high as OHC designs.
Modern pushrod engines are usually limited to about 6,000 RPM to 8,000 RPM in production cars, and 9,000 RPM to 10,500 RPM in racing applications. In contrast, many modern DOHC engines may have rev limits from 6,000 RPM to 9,000 RPM in road legal car engines and up to 19,000 RPM in current Formula One race engines, using pneumatic valve springs. High-revving pushrod engines are normally solid (mechanical) lifter designs, flat and roller. In 1969, Chevrolet offered a Corvette and a Camaro model with a solid lifter cam pushrod V8 (the ZL-1) that could rev to 8,000 RPM. The Volvo B18 and B20 engines can rev to more than 7,000 RPM with their solid lifter camshaft. However, the LS7 in the C6 Corvette Z06 is the first production, hydraulic-roller cam, pushrod engine to have a redline of 7,100 RPM. It achieves this feat vis-a-vis an ECU-controlled powertrain management system.
Limited cylinder head design flexibility - OHC engines benefit substantially from the use of multiple valves as well as much greater freedom of component placement and intake and exhaust port geometry. Most modern pushrod engines have two valves per cylinder, while many OHC engines can have three, four or even five valves per cylinder to achieve greater power. Though multi-valve pushrod engines exist, their use is somewhat limited due to their complexity and is mostly restricted to low and medium speed diesel engines. In pushrod engines, the size and shape of the intake ports as well as the position of the valves are limited by the pushrods.
Fred: PUSHRODS always work against Sir Isaac Newton's famous laws of Physics. Inertia: That force which keeps stationary objects at REST. And which also keeps moving objects in MOTION. KE= 1/2 (M) (V), squared. Kinetic Energy equals one-half the mass, times the velocity, squared.
I always loved to argue with my Mathematics and my Physics professors. I FLUNKED a lot of their exams, too....foolishly thinking I could BREAK...else find my way around...the inviolate principles of pure SCIENCE.
The "Quadratic Equation," it is a wonderful example. X= negative B, plus or minus the square root of 4(a)(c), all divided by 2(a). From the Calculus, it is a derivative of the basic expression, (a)(x) squared, plus (b)(x), plus (c) equals zero.
When YOU can find a BETTER way to determine "non-linear" functions, you let me know. YOU will be a candidate for the Nobel Prize in Mathematics.
Take 16 (sixteen) pushrods, weighing approximately 4-to-6 ounces each, factoring for distance traveled, per each cylinder combustion cycle. Be sure to assume that the camshaft rotates at one-half of the crankshaft RPM.
You should REALIZE that a LOT of kinetic FORCE is WASTED. YOUR Hewlett-Packard Scientific Calculator works just as good as mine, Buddy!
Overall, pushrod motors run about a 60-65 percent efficiency LOSS, against their DOHC brethren, all other things being equal.
I've already given you ONE exception to the rules, as in low-to-medium RPM diesel engines. They "lug" well, and they are cheap to manufacture.
Brush up on your Algebra and your Calculus, Fred. Review your "Statics and Dynamics" texts.
Next post, this old geeky "Inga-Neer" may hit you with a tough "pop quiz."