[Christ]

Glad you found that - now you know that working for primary harmonics is essentially worthless.

Now - if you double the frequency of the harmonics, you're still getting that boost, but slightly less of it, and in a slightly shorter RPM range. I haven't found a calc that will actually show you more than 4 harmonic ranges, but this falls into the "lots of valleys, and a specific peak" area.

It says that you would need a 35 inch runner to maintain ideal harmonics at a specific RPM (lets say 2100, since that's what my Prix cruises 65mph at (approx))

35 inches represents the approximate length based on the volume of the engine (and the assumed volume of the intake runner) where the frequency will be in 1:1 time with the engine's intake strokes. This means it's hitting the runner's end during the power stroke, and hitting the intake valve during the intake stroke, or traveling 1/4 the engine's RPM per the harmonic level.

So - if you need a 35 inch runner to maintain ideal harmonics at 2100 RPM, then a runner 17.5 inches will also work. Why? You have double the resonant frequency... the air is working at 2:1 with the intake valve. This means that it hits the intake valve during the period between compression and power, then again when the intake valve opens.

17.5 is still very long. Lets try 1/3 of the ideal frequency 35/3 = 11.666 is still too long.

.25(35) = 8.75 inches
.125(35) = 4.375 inches

You can't go much past 8 pulses... you really lose alot of the kinetic energy of the air even at 8 pulses.

The idea is compromise. You can't ideally have 35 inch runners, so you sacrifice some of the pressure wave in an attempt to salvage what power you can from a shorter tube. Remember, that every time you make the wave hit a surface, you're losing some of it's kinetic energy (ability to stuff air into the cylinder). This is why harmonics only work on a VERY short RPM range, and are generally not messed with.

One example of harmonic tuning on engines is with the 3.2 liter Yamaha V6 in the Ford Taurus SHO models. It has vacuum assisted valves which open or close based on engine RPM to allow shorter or longer runners to be used. At higher RPM, the shorter runners are used. There are two very specific RPM ranges at which this technology allows for a "bump" in the torque output.

Ideally, you would build an intake manifold which utilized "adjustable" runners, whose length would be controlled by the engine's RPM.