Carolina Horsepower - View Single Post

JohnnyP · 01-06-2008, 01:07 PM

Added the text of the installation to the Vampire page:
http://www.jandssafeguard.com/Vampir...S_Vampire.html

JJ@WMS just pm'd me, saying his two L's are down for mods for a while, but he may test it on a customer's truck that is coming in for heads and cams on a stock bottom end.

There seems to be a lot of interest in special coils, with the promise of increased spark energy.

The Vampire increases spark energy when retarding, because it extends dwell by the retard amount.

The equation for energy stored in the coil is:

E = 1/2 L *I * I

"L" is the inductance of the coil primary. "I" is the current flowing in the coil at spark time. Both of these can be measured, but for a given coil, inductance is constant, so we can ignore the L/2 term of the equation for this discussion.

With a stock dwell setting of 1.8 msec, a stock coil will achieve 6 amps of coil current. Note that the coil current ramps up, like a sawtooth. Zero current at start of dwell, increasing linearly with time.

For example, say the Vampire is retarding 10??. At 3000 RPM, 10?? is about half a millisecond (0.555). Add this to the stock dwell value of 1.8 msec, total dwell equals 2.355 msec, and the coil current will reach 7.8 Amps at spark time.

(7.8)/6 =1.3, or a 30% increase in coil current.

The energy equation says E goes up with the square of the current, so 1.3 * 1.3 = 1.69, or a 69% increase in energy stored in the coil.

At 6000 RPM, 10?? retard increases the current to 6.9 amps, resulting in 32% increase in coil energy.

For 1?? retard at 6000 RPM, dwell increases to 1.827 msec, current would increase from the stock value of 6 Amps to 6.09 Amps. 6.09/6=1.015, square this results in 1.03, or a 3% increase in coil energy.

For 2?? retard at 6000 RPM, current would increase to 6.18 A. 6.18/6=1.03, squared results in 6.2% increase in energy.

For 3?? retard at 6000 RPM, current would increase to 6.28 A. 6.28/6=1.046, squared results in 9.6% increase in energy.

This increased energy is stored in the magnetic field of the coil. When the field collapses at spark time, the energy is transferred to the plug.

This may seem small when compared to claims made by some coil manufacturers, but it's measurable. It's repeatable. I can take scope photos of it. I can hear the arc intensity increase in my pressurized spark chamber.

The Vampire IS an ignition amplifier when retarding.

01-06-2008, 01:07 PM	#6
JohnnyP Member Join Date: Jan 2008 Posts: 35	Added the text of the installation to the Vampire page: http://www.jandssafeguard.com/Vampir...S_Vampire.html JJ@WMS just pm'd me, saying his two L's are down for mods for a while, but he may test it on a customer's truck that is coming in for heads and cams on a stock bottom end. There seems to be a lot of interest in special coils, with the promise of increased spark energy. The Vampire increases spark energy when retarding, because it extends dwell by the retard amount. The equation for energy stored in the coil is: E = 1/2 L I I "L" is the inductance of the coil primary. "I" is the current flowing in the coil at spark time. Both of these can be measured, but for a given coil, inductance is constant, so we can ignore the L/2 term of the equation for this discussion. With a stock dwell setting of 1.8 msec, a stock coil will achieve 6 amps of coil current. Note that the coil current ramps up, like a sawtooth. Zero current at start of dwell, increasing linearly with time. For example, say the Vampire is retarding 10??. At 3000 RPM, 10?? is about half a millisecond (0.555). Add this to the stock dwell value of 1.8 msec, total dwell equals 2.355 msec, and the coil current will reach 7.8 Amps at spark time. (7.8)/6 =1.3, or a 30% increase in coil current. The energy equation says E goes up with the square of the current, so 1.3 * 1.3 = 1.69, or a 69% increase in energy stored in the coil. At 6000 RPM, 10?? retard increases the current to 6.9 amps, resulting in 32% increase in coil energy. For 1?? retard at 6000 RPM, dwell increases to 1.827 msec, current would increase from the stock value of 6 Amps to 6.09 Amps. 6.09/6=1.015, square this results in 1.03, or a 3% increase in coil energy. For 2?? retard at 6000 RPM, current would increase to 6.18 A. 6.18/6=1.03, squared results in 6.2% increase in energy. For 3?? retard at 6000 RPM, current would increase to 6.28 A. 6.28/6=1.046, squared results in 9.6% increase in energy. This increased energy is stored in the magnetic field of the coil. When the field collapses at spark time, the energy is transferred to the plug. This may seem small when compared to claims made by some coil manufacturers, but it's measurable. It's repeatable. I can take scope photos of it. I can hear the arc intensity increase in my pressurized spark chamber. The Vampire IS an ignition amplifier when retarding.