Last time I checked a swept volume of 717 + 71.7 of combustion chamber =788.7 With compression ratio being total cylinder volume (swept plus chamber) divided by the chamber volume, the compression ratio is 11.0:1 (788.7 / 71.7 = 11.0)
I suggest at least getting the math correct. And 100 feet cubed is not 100 cubic feet.
The article is accurate for the most part. The whole exhaust system needs to be considered for tuning.
The issue of collectors is one of definition: What is it and where do you measure its diameter to plug the number into a calculation? A merge collector can be smaller at the throat than at the discharge. Which diameter fits into the "2.75:1" rule, the throat or the exit? How long is its effective length when it is tapered? Old style collectors with the bundled primaries discharging into a tube that fit around them is much more like a resonance chamber on zoomies than most people believe. Therefore, those systems are tuned by primary length alone and have close to zero effective collector length.
Firing order is important as the pulse spacing impacts tuning diameters, lengths and pulse frequency versus the tuned pipe's natural frequency. In some V-8 racing applications, headers have some primaries from both sides collect in common to keep the pulse timing uniform. Some use the "double by Y" or the two into two into one.
What wasn't explained is the difference between steady state, slow and fast rpm acceleration rates on an exhaust system's performance. Any system will respond to varying engine acceleration rates differently. What works really well in first gear may not work quite the same in high gear. If you doubt this, I suggest you run a dyno test on the engine and exhaust system of your choice, only start at red-line and pull the engine rpm back to below 2,000 rpm by varying the load to de-accelerate the engine at the same rate (600 rpm second is common). The torque curve will be different than the one you ran with the engine rpm increasing. Why? This test is not possible on an inertia dyno so don't ask your local tuner to do it for you.
It takes time for a convergence of heat, flow velocity, pipe resonant frequency and wave systems to occur. The time can be very short or in some cases much longer, as in 0.4 seconds or more. Engines and exhaust with greater mass, displacement, and tuned lengths generally respond slower and will show greater disparity between steady state and fast acceleration tests.
So, will you run the salt flats, drag race 660 feet, or zip through the local curves on the way to lunch at your favorite brew pub?
