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Message: [QUOTE="cujet, post: 616204, member: 19501"] I run a turbo Miata with generally around 17PSI boost. The OEM ign coil is not really up to the task. So the use of NGK extended reach plugs (vs. stock) helps, but the mixture still won't ignite properly at high RPM under certain conditions. A switch to Bosch Platinum +4 plugs will work well and they last more that 20K miles before the problem returns. So, I have guessed that the proper ign coil would solve the problem. However the +4 plugs (the best I have found for my app) seem to be able function well. Certain engines are sensitive to gap issues and that is probably a function of getting the spark to the mix. Maybe a +4 type of plug would work well in these engines. Chris [/QUOTE]