I’m aware that EU-spec cars are equipped with gas particulate filters (GPF/OPF) which mute sound compared to cars exported to the States and Canada. Does anyone know if Japan-spec 992s have this OPF?
Secondly, does the filter affect performance/top-end acceleration at all?
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Not sure but I think US cars have opf, just not monitored. I know my 718 does.
Yup.
Opf delete is a popular mod to increase power and/or sound. Not sure if the efficacy, though. My race shop says most power is gotten from the header mods.
Correct, any horsepower gained from removing the non-functioning OPF could be attributed to natural variance, there’s maybe 2-5 hp in it. With that said, replacing the OPF with standard over axle pipes helps the sound tremendously.
Going to an catless or high flow cat header will give moderate gains that are more than just variance.