Splitfire, Autolite and Champion
#5 (first plug on drivers side) Champion 401 (RS12YC)
NGK TR5 comparison
NGK TR5 IX Iridium
I have tried all 6 of the plugs shown in the pics above. My favorite is still the Splitfire after all the testing that I have done. The stock plug and Autolite have the flattest throttle response of all the plugs with the Autolites being the worst. The Splitfire had the best throttle response but the NGK is not too far behind. The TR6 ran one and a half miles per hour less trap speed at the track than the Splitfire. I didn't think it was the plugs at first but when the Splitfires went back in the MPH came back. I have never had a detonation problem until the #4 pulley and new winter gas formulation. I put the TR5 plug in at the same time the gas changed and had some pinging. I thought it was the plugs so I decided to try the Champion 401 (big mistake). I could not hear any detonation with the Champions but less than 2 days after installation the # 5 plug was destroyed and luckily did not result in any engine damage. I put Splitfires back in and there was detonation again. I had my chip reburned for the sorry winter gas and kept my warm weather program on Side II of my flip chip. I will retry the TR5 to see how it does. So far so good with the TR5's (see pics above) but the track will the whole story. The TR5's gave me the same response and MPH at the track so they are keepers. I also had good luck with the TR5IX Iridium plugs. The only real benefit to the Iridium is a smoother idle for $57 vs. $14 for the regular TR5.
#1 Plug Removal Video Part 1
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#1 Plug Removal Video Part 2
Note: The number of threads holding the plug in is shown by the compound missing on SF10D. If you have any pinging or clatter at Wide Open Throttle DO NOT ignore it . Any plug will fail if detonation occurs continuously. Get you chip reburned so that you don't damage your engine.
Sparkplug Replacement Tips and Tools