[vortec57L]

Hi guys,

As for the ignition side of things, my truck came with NGK Iridium plugs from the previous owner - Victorian Government Ambulance Service (AUSTRALIA).

From speaking to a few techs from the Victorian Ambulance Service, they were using Iridium plugs not for performance, but higher milage for longer service intervals. They used the Iridium plugs when the factory Delco Platinum plugs reached about 100,000kms. They used Iridiums to cover between 100,000kms to 200,000kms. BTW, the vehicles are removed from service once they have done 200,000kms. My truck has 205,000kms, and the plugs are still firing well. I have a set of Accel Truck Plugs from their Super Truck Tune Up Kit ready to fit, if my old Iridiums wear out.

You can regap Iridium plugs! I removed mine a few weeks ago the gaps were from 0.025" to 0.055" when they are supposed to be 0.060"

I worked for Toyota in Australia when Denso (owned by Toyota) was releasing their Iridium plug. One of the techs was telling me that they could provide a 8KW (about 10hp) gain at the rear wheels. He showed me a Dyno report on a Toyota Landcruiser 4.7L V8 (Similar to US market Lexus LX-470).

Here is some tech info from NGK's Australian website:
"The following matrix gives an example of the characteristics and service life of resistor spark plugs when used in a modern unleaded engine:

Type Service Life Benefits
Nickel Alloy 20,000 - 40,000 kms Standard style of spark Plug.
Nickel Alloy (V-Groove) 20,000 - 40,000 kms Improved ignitability due to sparking at periphery of the electrode.
Platinum 0.8 mm dia. 100,000 kms Long service life and even better ignitability due to a small diameter centre electrode
Iridium IX 0.8 mm dia. 160,000 kms Extremely long service life. Same level of ignitability 0.8 mm dia. Platinum
Iridium IX 0.6 mm dia. 60,000 kms Long service life. Same as 0.8 mm dia. of Platinum and extremely good ignitability characteristics. (Better than 0.8 mm dia. platinum or 0.8 mm dia. iridium)

The use of Iridium spark plugs is only just starting with Japanese car manufacturers who are finding them ideal for very low emission engines."

In my opinion for a 1996-00 OBS 5.7L V8 ingition upgrade, I would get the following:
1. Replace stock plugs with a good set of plugs gapped to 0.060" eg NGK V Groove, Bosch Platinum, AC Delco Rapid Fire, Accel Truck Plugs, etc
2. Replace factory distributor cap and rotor with a performance replacement eg Accel
3. Replace cheap factory spark plug leads with MSD Super Conductors (only about 50 ohms resistence per foot), which are well shielded to work with PCM and similar electonics
4. Replace stock coil with a MSD #8231 or Accel #140024 performance replacement coil.
5. Fit Mallory Hyfire 6-A or MSD 6A ignition amplifiers wth MSD #8877 harness adapter (regap plugs to 0.070")

I first did steps 2 to 4 on my truck, and these upgrades made the motor smoother at idle. Step 5 made the motor idle very smoothly, and reduced fuel consumption around town by about 1 to 2 MPG.

Cheers,
ANDREW