Need help with coil.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,361
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Need help with coil. (DollaGreen)
If I can offer a few comments and suggestions on the various topics I've seen in this thread:
1. Coil mounting bracket:
For a correct bracket to mount the coil upright (vertically) to the intake manifold in the stock position, order part number L8 from Year One. Price is $29. You can see the bracket at http://www.yearone.com/serverfiles/f...ain2.asp?cat=8
This will put the coil in a nice location, and it will work very well.
On this subject:
I have seen a lot of discussion about mounting the coil on the firewall to get it away from the "excessive" heat of the engine. A coil mounted to the stock bracket on the intake is actually raised above the intake by about an inch or so. The intake is one of the coolest parts of the engine. The temperature difference between a coil mounted an inch above the intake or on the firewall 3 inches behind the intake is so miniscule that it truly makes no difference in coil performance.
Does coil temp make a difference? The resistance through a copper wire changes with temperature. As temperature goes up, resistance goes up. Likewise, the cooler the wire, the lower the resistance. Thus, a cool coil will flow more current than a hot coil. The more current you can flow through the coil primary windings, the better saturation you get, and the stronger the secondary voltage (spark). A coil operating at 0 degrees F will probably have a measurably better level of performance than a coil operating at 300 degrees F. But I truly doubt that you'll see a measurable performance difference between a coil running at 150 degrees versus one running at 190. So save yourself some hassle, and save thoe holes in the firewall, and just mount the thing to the stock bracket.
2. Mounting the coil upright:
The coil is filled with oil to prevent hot-spots in the coil primary windings. Obviously, since the primary windings are a resistance, and you're flowing current though them, the coil generates heat. The more current you flow, the hotter it gets. If the coil is laying on its side, it is possible to expose a small portion of the windings, creating a hot spot and a possible failure point.
Normally, this is not a big issue. However, when running "CD" ignitions (which means "capacitive discharge"), the effective dwell is actually increased, resulting in higher-than-normal current flow through the coil. Further, most CD ignitions run a full 12 volts to the coil, without the use of a ballast resistor (see next topic), further increasing the wattage of the coil and its operating temperature. This all improves coil saturation, and therefore spark intensity, but also increases the heat output of the coil significantly. Thus, it becomes more important that the coil be fully immersed in the oil and that no windings be exposed by placing the coil on its side.
3. Coil input voltage and ballast resistors:
When running a standard point-style ignition system, the input voltage to the coil (the wire running to the "+" side of the coil) must be below battery (system) voltage - usually about 7 volts-or-so. Running the points on 12 volts will result in rapid point failure. All stock GM cars with points use a resistor wire in the "+" circuit, which drops the voltage down to the acceptable level - there is no need to use an additional ballast resistor in addition to the stock resistor wire, unless the resistor wire has been removed , bypassed or damaged. To test your resistor wire circuit and to verify that it is doing its job, you can do as follows:
Disconnect all wires attached to the coil except the resistor wire on the "+" side. (NOTE: There are usually 2 wires attached to the "+" side: the resistor wire from the ignition switch, and a second wire from the starter solenoid "R" terminal. You can identify the resistor wire by turning the ignition to the "on" position and testing for voltage: the resistor wire will have voltage in the "on" position, but the wire from the solenoid will not.) Then, run a wire from the coil "-" terminal directly to ground, grounding the coil (this is what the points do when they are in the closed position). Turn the ignition to the "on" position and test the voltage at the coil "+" side. If you have a correctly functioning resistor wire, the voltage will be somewhere between 6-8 volts. If you do not have a resistor, you will read very close to battery voltage. If this is the case, you must use a ballast resistor to get the voltage dropped.
When running PerTronix, MSD and other electronic and CD ignition systems, this often changes. PerTronix conversions require that a full 12 volts be applied to the system - use of a resistor wire or a ballast resistor will cause a PerTronix system to misfire. Likewise, on an MSD, the points are merely used to trigger the MSD control module, so the system must be hooked up as shown on the MSD installation instructions. The resistor wire (or ballast resistor) is not used, and a full 12 volts is normally applied. This increases the wattage of the coil, and further contributes to its heat generation, making installed orientation more critical.
Hope this all adds more confusion to the issue.....
1. Coil mounting bracket:
For a correct bracket to mount the coil upright (vertically) to the intake manifold in the stock position, order part number L8 from Year One. Price is $29. You can see the bracket at http://www.yearone.com/serverfiles/f...ain2.asp?cat=8
This will put the coil in a nice location, and it will work very well.
On this subject:
I have seen a lot of discussion about mounting the coil on the firewall to get it away from the "excessive" heat of the engine. A coil mounted to the stock bracket on the intake is actually raised above the intake by about an inch or so. The intake is one of the coolest parts of the engine. The temperature difference between a coil mounted an inch above the intake or on the firewall 3 inches behind the intake is so miniscule that it truly makes no difference in coil performance.
Does coil temp make a difference? The resistance through a copper wire changes with temperature. As temperature goes up, resistance goes up. Likewise, the cooler the wire, the lower the resistance. Thus, a cool coil will flow more current than a hot coil. The more current you can flow through the coil primary windings, the better saturation you get, and the stronger the secondary voltage (spark). A coil operating at 0 degrees F will probably have a measurably better level of performance than a coil operating at 300 degrees F. But I truly doubt that you'll see a measurable performance difference between a coil running at 150 degrees versus one running at 190. So save yourself some hassle, and save thoe holes in the firewall, and just mount the thing to the stock bracket.
2. Mounting the coil upright:
The coil is filled with oil to prevent hot-spots in the coil primary windings. Obviously, since the primary windings are a resistance, and you're flowing current though them, the coil generates heat. The more current you flow, the hotter it gets. If the coil is laying on its side, it is possible to expose a small portion of the windings, creating a hot spot and a possible failure point.
Normally, this is not a big issue. However, when running "CD" ignitions (which means "capacitive discharge"), the effective dwell is actually increased, resulting in higher-than-normal current flow through the coil. Further, most CD ignitions run a full 12 volts to the coil, without the use of a ballast resistor (see next topic), further increasing the wattage of the coil and its operating temperature. This all improves coil saturation, and therefore spark intensity, but also increases the heat output of the coil significantly. Thus, it becomes more important that the coil be fully immersed in the oil and that no windings be exposed by placing the coil on its side.
3. Coil input voltage and ballast resistors:
When running a standard point-style ignition system, the input voltage to the coil (the wire running to the "+" side of the coil) must be below battery (system) voltage - usually about 7 volts-or-so. Running the points on 12 volts will result in rapid point failure. All stock GM cars with points use a resistor wire in the "+" circuit, which drops the voltage down to the acceptable level - there is no need to use an additional ballast resistor in addition to the stock resistor wire, unless the resistor wire has been removed , bypassed or damaged. To test your resistor wire circuit and to verify that it is doing its job, you can do as follows:
Disconnect all wires attached to the coil except the resistor wire on the "+" side. (NOTE: There are usually 2 wires attached to the "+" side: the resistor wire from the ignition switch, and a second wire from the starter solenoid "R" terminal. You can identify the resistor wire by turning the ignition to the "on" position and testing for voltage: the resistor wire will have voltage in the "on" position, but the wire from the solenoid will not.) Then, run a wire from the coil "-" terminal directly to ground, grounding the coil (this is what the points do when they are in the closed position). Turn the ignition to the "on" position and test the voltage at the coil "+" side. If you have a correctly functioning resistor wire, the voltage will be somewhere between 6-8 volts. If you do not have a resistor, you will read very close to battery voltage. If this is the case, you must use a ballast resistor to get the voltage dropped.
When running PerTronix, MSD and other electronic and CD ignition systems, this often changes. PerTronix conversions require that a full 12 volts be applied to the system - use of a resistor wire or a ballast resistor will cause a PerTronix system to misfire. Likewise, on an MSD, the points are merely used to trigger the MSD control module, so the system must be hooked up as shown on the MSD installation instructions. The resistor wire (or ballast resistor) is not used, and a full 12 volts is normally applied. This increases the wattage of the coil, and further contributes to its heat generation, making installed orientation more critical.
Hope this all adds more confusion to the issue.....
Drifting
Joined: Aug 2002
Posts: 1,731
Likes: 22
From: Marietta Ga.
Re: Need help with coil. (lars)
Lars :cheers: :cheers: Thanks for the info. I now know more than I did about coils. As my screen name says, I am a crusier not a brusier, so I will stick to stock for now. Keep 'em coming, I like this learning stuff. :seeya
