Chuck - does "C" represent the estimated cost of conversion or the actual cost (after one buys all the things one didn't think about in the planning stage
)?
Actually, glad to see you did the equation. I was too lazy to do one. Your examples point out very distinctly that a finite increase at a higher initial point is requires a much longer payback period.
Would like to throw one other issue in this discussion. Most would assume that the Q-Jet (spread-bore) will always do better on fuel economy than a square-bore; but this is NOT ALWAYS true.
Many years ago, I converted a motor home with a 454 from a Q-Jet to a custom Carter AFB due to lack of low-end torque with the small primary bores of the Q-Jet. Both the Q-Jet and the AFB were 750 CFM. After the conversion, the power difference was astounding. The difference was measurable in that we dropped driving time from our residence to Hershey, PA from 20 to 18 hours (with the cruise set at the same speed). The difference was maintaining that speed in the mountains. However, when we figured fuel economy, we were very pleasantly surprised to see that our MPG climbed from 6.3 to 7.2. I would have been happy to break even. The key here is the mass (weight) of the vehicle. The small primary of the Q-Jet simply was not large enough.
Every application is different; which is why there is never a single "right" answer.
Jon.
