I just installed NGK TR55ix iridium plugs and MSD 8.5mm SuperConductor wires. The iridium plugs are fairly expensive compared to all the others but from what I have read, they work quite well. Have not heard anything good about the Bosch +4 plugs. When I removed the original AC plugs, only 1 out the 8 had the platinum puck remaining on the electrode.
As far as wires, MSD wires are supposed to have the least amount of resistance in ohms (50 or less ohms per foot) and are comparable in price. I got mine in red from Summit Racing.
Doing plugs and wires is a real PITA in LT-1 C4's. The local Chevy dealer wanted 8 hours labor for the wires! The passenger side is not too bad as you can see the Opti and everything is straightforward. The wires on the driver side are a real pain. I wound up removing the alternator, idler pulley, tensioner, moved the A/C compressor out of the way and the PS pump had to go forward about 2 inches as the OEM wires pass behind the pump and through a small bracket. Once all of that was removed or relocated, I could actually get my hands down to the Opti. Not a lot of room to grab the old wires, but I did get them. It didn't even take a long time to clean up the blood off the motor. Hopefully, the little neighbor kids didn't learn too many new words.
If you pull both the center and rearmost part of the lower fender wells, that should get you fairly easy access to the plugs. At least 2 10" 3/8 drive extensions, a swivel and a spark plug socket will get the plugs out. #8 plug is pretty hard to do but small hands help with that one.
Be careful with the install of new plugs. Use antiseize on the threads and torque to about 11-12 ft.-lbs. Use a piece of hose on the end of the plug to help with starting the threads. You don't want to cross thread the aluminum heads!! Use dielectric grease on both ends of the wire boots. The coil wire is suprisingly not too difficult even though the boot on the opti is down a hole. Remember to twist the wires 1/2 turn on the opti to remove them.
The factory plug wire looms will have to be reamed out to accept anything bigger than 8mm wire. I did not reinstall the rear looms that bolt to the heads. OEM wires will have a plastic spiral wrap on them. You can carefully unwrap them and re-use on new wires.
