I’m in Sydney & have PPE headers on my ISF, & I like them. they make the ISF a little nosier inside the cabin, but it’s a nice rumble sound. most things you do to n/a ISF won’t give you huge gains, like sticking a supercharger on, but you do notice them, & they all add up to a good gain, & a great sound. Like BLK ISF said, headers would give more kw, than a cat back exhaust, & so on.
It’s a big job to fit the headers to the ISF, & must be fitted from under the vehicle. they have to drop the front sub frame and steering box off, while they support the engine. the steering column shaft goes through the right hand side header. I would only trust someone that has done many ISF’s before.