Cat-free header systems with hi-flow cat in frontpipe
 

From a quick search I can find that APEXi, HKS, and fujitsubo offer catfree header -> front pipe systems with high flow catalyzers in the front pipe. However, APEXi seems to be the only manufacturer that bothered to relocate the second O2 sensor to after the high flow cat.

Anyone know why HKS and fujitsubo didn't bother to relocate the sensors? From the experiences shared by APEXi owners, they did not get a CEL after installing their system.

Is it because all header upgrades should follow with a tune which will take care of the CEL anyways?

Most likely.

Ideally you'd get a tune.

Having the O2 relocated to after the secondary cat is no guarantee you'd get no CEL. Most that don't relocate just provide you with an O2 spacer.

If you get a non-oem header you would be crazy not to get a tune also. You are leaving drivability, reliability and power all on the table.

HKS does relocate the second sensor behind the cat. It also includes an extended bung for the sensor. Though it also comes with a plug if you don't want to relocate it. That's what I did with mine.

Oh interesting i didn't know that. i wonder what the difference is between HKS and APEXi then because they look exactly the same with similar sized cat

HKS comes with overpipe and frontpipe as well right?

No overpipe unfortunately. Just the header and front pipe. But you won't gain anything from an aftermarket overpipe. But HKS does make their own now.

I'm sure there are some slight differences. I know the muffler design is different, but the catalytic might be sourced from the same company. I'm sure you would like either one, though the HKS is the cheapest of the three.

Get a tune with a header. No good reason not to. An extended bung just takes the O2 sensor out of the stream which can stop a CEL. But get a tune it’s worth it, even an OTS tune.