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Subaru WRX STI (2015–2021) Ignition FAQ's

Please read our FAQs page to find out more.

What spark plug heat range suits a tuned EJ257?

One step colder than stock is common for elevated boost. Gap to your tuner’s spec—tighter gaps often help resist blowout under load.

Are coil upgrades worthwhile on the STI?

Quality coils can improve spark energy and consistency with higher cylinder pressures. Pair with the correct plugs and dwell settings.

Why does my STI misfire only at high load?

Usually plug gap, aging plugs, marginal coils, or a boost leak. Verify fuel quality and tune health before pushing harder.