Install: HKS Twin Scroll Downpipe (JDM)

I finally picked up a downpipe for my EJ207 v8 Bugeye. I initially leaned toward the Lachute catted downpipe, but I happened to see this one on Nasioc for cheaper. It is USDM in length and comes with an extra O2 bung for a wideband sensor. I prefer catted downpipes, the cat acts as a resonator and cuts down on the rasp, and obviously, it is cleaner.

I didn’t see this damage in the photos nor in the description but it looks like someone bottomed out the downpipe on the pavement. Not thrilled about it but it will still work.

The downpipe goes down to a 2.625-inch (65mm) OD to connect to the stock midpipe. The problem is the OEM donut gasket has a 2.5-inch ID, so that it won’t fit the HKS downpipe. I thought about cutting off the extended pipe and running a flat gasket, but I like the donut gasket. They seal better and allow some movement with the spring bolts.

I found this gasket on Amazon. It fits the HKS downpipe perfectly. The mid-pipe and spring bolts are another story.

And finally we can transfer the remaining items over to the new downpipe and it it is all set to go back in the WRX.

On first start, it is way louder than before. I was a little taken aback. However, once the engine warms up it is pretty quiet. There is still drone at 3,000 rpms, not that I expected this to fix it.

I am still in the process of getting my e-tune dialed in, but throttle response seems to be a lot better. Full boost seems to hits around 3,500 rpm and it absolutely wails at WOT.

The old downpipe was cracked in two places at both ends of the resonator. Considering how many cracks this exhaust has had, I wonder if this car was in a light accident or something. The headers and the downpipe have both cracked.

That said, I am thinking about cutting the resonator open to see what’s inside before I send it to the metal recycler.


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