High output ignition coils

[s2dman]

I have never seen a discussion about using higher output coils on Turbo Dodges. They seem to help on non turbo cars and I wondered if anyone has had any luck with our cars? Thanks, Dan
'87 CSX
'89 CSX

[Ondonti]

im using the coil from a 5.0 mustang on my car. supposed to be a little better than stock.

[tonyz2897]

I've heard of people having problems with the stock coil at high boost levels. Heck even my car at only 25 psi seems like it's losing fire occasionally. I just bought an Accel SS coil to hopefully solve that problem.
Tony

[iTurbo]

I have a '90+ style MSD Blaster coil (#8228) on my Shelby Lancer, along with some Magnecor wires. I haven't had a problem with up to 20 psi boost yet. I can't really say how the stocker compares because I was only running 14 psi back then.

[DblTrbl]

The higher the octane and the higher the cylinder head pressure and the larger the spark gap, the harder the charge is to light.

One of the things that concern me is that the fuel pump circuit and the + side of the coil are shared. This becomes a bigger problem when we add a higher flowing fuel pump and run it at higher pressure because we have higher boost. Because of the higher load from the fuel pump, there is a bigger voltage drop in the wires and this means that the + side of the coil is getting a lower voltage. A lower voltage means that the coil will not charge as well for each spark. This becomes even worse when we start adding a performance coil. These performance coils usually have lower impedance primary than stock coils which means they draw more current.

On my setup, I've created a whole new circuit for the coil. It is powered directly (through a fuse) from the battery and through a new relay. The relay is turned on by the old shared circuit. This means that the pump is now all by itself on the old circuit and the coil is all by itself on the new circuit. The coil is still only powered up when the ASD circuit is closed, but now it does not share wires with the pump. Use at least a 16 guage wire (14 or 12 is even better).

Carl
SC 11.5 @ 120 on street tires

[xrattiracer]

the stock coil has been proven to work just as well as any other coil up to a certain power level, at which point the spark gets blown out and you definantly know there is a problem.
neat idea with the seperate circuits, but a bit backwards; the fuel pump draws much more current than the coil and as such it would make more sense to have it be on its own circuit. which i believe it is on all the cars after 85 or so.

[s2dman]

Thanks to you all for the input.
Dan

[DblTrbl]

Quote:

Originally Posted by xrattiracer the stock coil has been proven to work just as well as any other coil up to a certain power level, at which point the spark gets blown out and you definantly know there is a problem. neat idea with the seperate circuits, but a bit backwards; the fuel pump draws much more current than the coil and as such it would make more sense to have it be on its own circuit. which i believe it is on all the cars after 85 or so.

Cars after 85 do not have their own circuit. All the cars I've had up to and including 89 have a shared circuit. If you want to test if a cars circuit is shared, then just momentarily hook up a jumper between the + side of the battery to the + side of the coil. If you hear the fuel pump start, then it's shared.

I'm not so sure which of the two are better to replace. Certainly, everyone agrees that seperating them will help both the fuel pump and the coil. Which one of the two circuits should be replaced first is best decided by which of the two are closer to being maxed out in each application. For example if you are not getting enough fuel, then replacing the pump circuit would be advisable. If you are getting your spark snuffed out by high boost and high octane, then replacing the coil circuit would be advisable.

Also keep in mind that the fuel pump and the coil draw current in a different manner. The fuel pump draws a steady high current. The coil turns on and off and therefore has a very high inrush current followed by a period of diminishing current and then by no current draw. This happens thousands of times per minute. I would venture to guess that the inrush current on a coil would be close to if not greater than the average current of a fuel pump. Although the average draw of the coil is less than the average draw of a pump, it is the inrush current that is critical for charging a coil to it's maximum potential. Inrush current is what dims your lights when you first turn any electical circuit like a refrigerator or compressor on.

[Frank]

To further explain what Carl said...

What happens is that when you open the circuit to the coil (this is when you want to fire the cylinder), the electromagnetic field in the core of the coil/transformer collapses, sending voltage of around 125 volts into the primary circuit, and causing a massive voltage discharge on the secondary side of the coil/circuit. This is what actually creates the 20,000+ volt discharge seen on the spark plug. Of course this is when the available current drops because it has to reenergize the coil field like Carl said. The higher the RPM, the more the coil has to do this so the average current usage goes up. In addition, there is back-EMF protection to the transistors & relays that open/close these circuits.

Frank