Hi Bob,
FWIW:
In all of the different Model A opinions expressed today & in the past, and in all of the numerous different Model A performance religions believed in, one (1) Model A Faith we can hang our hat on is what is often written about, e.g., the Model A religion preached through human "experience" after one uses a fully "calibrated" Dynamometer as a mechanical Diety to express the truths for improving Model A performance. Reply #3 & reply #6 appears to echo this concept.
A few years ago, in speaking to Mr. Ron Kelley on increasing Model A engine performance he casually mentioned what most race car enthusiast are aware of, i.e., "Porting".
He mentioned that through experimentation he found in using his dynamometer that the first & most inexpensive & functional method to gain horsepower on a Model A engine was simple "Porting".
For example, he instructed me to first:
1. Use one's finger to "feel" inside the engine block for cast iron sharp edges, i.e., inside the intake & exhaust ports, to feel for roughness & sharp casting edges and to carefully & slightly ease these sharp turns & surfaces with a Dremel tool into smooth surfaces but being cautious not to cut into the engine's water jacket.
2. Do the same with the inside surfaces of the Model A intake manifold.
3. Remove the sharp lip under all valves & slightly round same, & slightly round tops of all valves to eliminate sharp turns which can create flow turbulence.
4. Check smoothness of the carburetor venturi & top opening of carburetor.
5. Do not allow the carburetor to manifold gasket protrude into the intake opening & cause turbulence instead of allowing unobstructed smooth flow.
6. After doing the above, he mentioned one can obtain maximum performance out of a standard engine or later for example, maximum performance out of adding for example, a high compression head, a B carburetor, and or a higher lift cam.
7. The speed of air flow & liquid flow depends greatly on smooth surfaces & smooth changes of direction. A good example is to watch fast moving water flowing in a very smooth concrete ditch as opposed to much slower water flowing in a rough earth ditch lined with 6" high grass; or watch the sloped angle in which water runs rapidly off of a metal standing seam roof as compared to slower flowing water dropping straight down 90 degrees off of the edge of a rough aggregate surfaced asphalt shingle roof with the same slope.
8. In my humble opinion, this was just one Model a guy's opinion, but tested with his calibrated dynamometer as opposed to sticking his head out of the window to listen to the exhaust difference; or holding one's hand out of the window to check the speed of the breeze while giving it the gas to test increased engine performance.
9. All I can mention is in following Mr. Kelley's advice with porting, and after installing a .330 cam, a Police Head, a B carb, & a B distributor, eyebrows raise when I take off from a red light.
Just hope this helps.
