quote:Originally posted by 1FASTV8:
Can anyone tell me why that is? Because I don't see ANY reason at all for it.
"The 6.1 and/or newer 5.7's with the shorty plug deseign have bigger more powerfull coils. The 03-05 trucks use two coils to fire each cylinder and they are staggered by 1/2 timing degree.
This is what I found:
There is less spark energy to both of the spark plugs in any given cylinder when the shorty spark plug wires are used. With the stock spark plug wire setup only one spark plug per coil is under the load of compression when that particular coil is fired, the 2nd spark plug that crosses over to the paired cylinder with a spark plug wire is not under compression when the coil is fired allowing full current to the spark plug in the cylinder that is firing on the compression stroke.
There are eight coils and they are each fired twice per combustion cycle, once just before top dead center (TDC) on the compression stroke and again just before TDC on the exhaust stroke. This is called a waste spark ignition system because the firing on the exhaust stroke really doesn't do very much.
The stock coil and spark plug wire setup was originally designed so that each spark plug in any given cylinder could be fired at a completely different time than the spark plug right next to it in the same cylinder because they are fired from two different coils. With the stock setup you could fire one spark plug in cylinder #1 (the spark plug directly attached to cylinder #1 coil) at 26 degrees before TDC compression and then fire the second spark plug 6 crankshaft degrees later at 20 degrees before TDC. The second spark plug in cylinder #1 is connected to and fired from the cylinder #6 coil with the crossover spark plug wire. The 6 degrees of stagger between the firing of the two spark plugs in the same cylinder is extreme and is only used as an example but, there is .5 (1/2) degrees of stagger in the firing of the two spark plugs in the same cylinder with the factory calibration and spark plug wire setup.
When you install the shorty spark plug wires you lose the .5 degrees of spark advance stagger as well as have less spark energy to the spark plugs in the cylinder that is firing because you are now firing two spark plugs under compression per coil instead of only one.
Firing order 1-8-4-3-6-5-7-2
1 & 6
8 & 5
4 & 7
3 & 2
Ex. Stock wire setup: Cylinder #1 piston is coming up to TDC on its compression stoke and its paired cylinder (cylinder #6) is also coming up to TDC on its exhaust stroke at exactly the same time. At 20 degrees before TDC compression cylinder #1 coil is fired which fires one spark plug directly under the coil in cylinder #1, which is under compression, and a second spark plug in cylinder #6, which is not under compression, and is connected to cylinder #1 coil with the crossover spark plug wire. The spark plug in cylinder #6 does not place the cylinder #1 coil under a heavy load because it is not firing against compression. A fraction of a second later at 19.5 degrees before TDC compression on cylinder #1 (.5 degrees of stagger) cylinder #6 coil is fired which fires one spark plug directly under the coil in cylinder #6, which is also not under compression, as well as the second spark plug in cylinder #1 that is under compression and is connected to cylinder #6 coil with the crossover spark plug wire.
Hemi crate engines use a manual throttle body and 4.7L PCM code. 4.7L code does not use a dual spark plug staggered waste spark ignition system so the eight factory coils on the crate engine are only fired once per combustion cycle instead of twice, which allows the use of shorty spark plug wires on the crate engines.
2006 and newer 5.7L’s as well as all 6.1L’s do not use a waste spark ignition system and have coils that are much larger to fire both spark plugs in the same cylinder at the same time . These coils are only fired once per combustion cycle instead of twice like the 2003-2005 5.7L coils.
When the 6.1L coils are installed on a 2003-2005 5.7L with the PCM still programmed for a dual staggered waste spark ignition system the 6.1L coils will be fired twice per combustion cycle instead of only once like they were designed to do. So if my math is correct at 6000 RPM the coils should be fired 50 times per second (6000/60=100 100/2=50 (4 stroke))? With the 2003-2005 PCM code the 6.1L coils will be fired twice as many times or 100 times per second instead of only 50?
Run any wires or coils that you like, these are only the facts as I known them to be true.
Guys running forced induction have already found out that the shorties are not the way to go. The 6.1L coils are your best bet but, the PCM should be reprogrammed for them to work at 100% efficiency."