Late Model Hemi Ignition Coil Dyno Comparison
http://www.moparmax.com/tech/2012/vii_7 ... oil-1.html
Classic and late model Mopars couldn’t have different ignition systems if they tried. Back in the day high voltage spark was distributed to the spark plugs by a mechanical distributor. There was a single coil that generated the high voltage for all eight cylinders. A mechanical shaft spun by the camshaft rotated a rotor which sent the generated high voltage via an arc across an air gap to a distributor cap terminal. There the high voltage pulse traveled down a long wire to the spark plug. These high voltage ignition wires had to be thick and well insulated against heat and voltage leakage.
Late model cars use individual coils for each cylinder, usually referred to as “coil packs.” This “coil-on-plug” design requires that only low voltage be routed to each cylinder. Once the low voltage trigger signal reaches the coil pack, the signal is transformed up to a high voltage which only needs to travel a couple of inches from the coil to the spark plug.
The coil-on-plug system avoids the pitfalls of having high voltage travel long distance in vulnerable wires to the spark plugs. More importantly, the old distributor design only allows for spark advance/retard on a global scale for the car, any advance or retard occurs equally for all cylinders. The coil-on-plug design allows the engine control computer to adjust the spark curve on the fly for each cylinder individually (on some cars) thus maximizing efficiency which is important for fuel mileage and emissions control.
Old school factory single coil systems were not known for their amazing voltage output. A very common mod was to upgrade to a better quality aftermarket coil and ignition wires. With modern coil-on-plug systems, very few people both to upgrade their systems. As our testing proved, this is a shame as there is power to be found even in the late model system.
In theory, a higher voltage spark cannot gain horsepower per se. If the ignition system is working perfectly, meaning that every power stroke of every cycle for every cylinder is ignited by the plugs then there is nothing else to do, the fire is lit. In other words, the only way an ignition upgrade can gain horsepower is if there are misfires, some power strokes where the mixture isn’t ignited, or at least not fully ignited, in the cylinder. Put another way, ignition system upgrades generally can only gain back power that is being lost due to incomplete ignition occurring.
We contacted MSD, well known for their broad line of ignition related products and got our hands on a set of their Blaster coil packs, part number 82568. According to MSD, these coils are made to higher quality specs then the factory coils. MSD left the voltage the same as factory, they found this voltage was sufficient for stock or near-stock engines and by using the stock voltage there is no need to change spark plug gap or heat ranges from stock specs. MSD says these coils are intended for people wanting to replace their factory system with higher quality parts and superior reliability. And they look really cool with their red molded plastic bodies.
We also contacted Granatelli Motor Sports and got a set of their Hot Street high performance coils, part number 28-0504-CP. Granatelli took a different path from MSD and changed the specs of the internal windings on these coils to produce higher output voltage. Granatelli says you don’t need to change your plugs for these coils. The Maulin’ Magnum uses non-stock plugs on her Magnuson supercharged engine anyway, so it was a moot point.
Granatelli Motor Sports kindly let us thrash their dyno to test the stock ignition against the MSD Blaster coils and the GMS Hot Streets. The results were both expected and surprising. Expected because the MSD coils performed exactly as MSD said they would, matching the horsepower output of the factory coil packs down to the exact horsepower within one foot pound of torque. Unexpected because we didn’t think there was any horsepower being left on the table by the factory system and yet the Granatelli Hot Street coil packs found almost 11 extra horsepower and a tad over 12 pound feet of torque hiding in our engine. We happily rolled out of the Granatelli shop and headed home with the Hot Streets installed and wondered how they’d work in the real world and at the track.
The first thing we noticed was how smooth the Maulin’ Magnum idled with the Hot Streets. A couple of times over the next few days when we had the radio volume up really high and couldn’t hear the engine idling at a red light, we thought the car had stalled. We had to look at the tach to see that it was still running. We hadn’t realized that the car was rocking a little bit at idle with the stock coils until the new coils smoothed out the idle so much. As to the track, the Magnum has always been strong and pretty consistent, but seems to have gotten a little more consistent which is good for dial and index racing.
11 extra ponies and 12 lb. ft. torque increase is impressive from just a change in coil packs. The GMS Hot Streets are a bit more expensive than the MSD Blaster coils, which are about the same price as factory coils at our local dealership. We can’t speak to how either of these aftermarket coils will work on stock motors with no power adder, so we’ll let you and your wallet decide what to buy. The factory coils are surprisingly effective, the MSD Blasters look to be very robust and make a nice upgrade, and the GMS Hot Streets seem to be the ticket for power adders and if you’re looking for all of the horsepower your engine has in it.
