civic ek4 highflow cat questions


New Member
Jun 8, 2018
civic ek4 vti '99
Hi everyone! My name is Aris and I 'm totally new in this forum.
The last 12 years I own a '99 civic ek4 vti with 175.000km on it. It has basic mods and bolt-ons such us:

Bilstein B6 suspension
HR springs
Spoon torque damper
oem airbox with a k&n drop in filter
Accel spark plug wires
54mm handmade cat back exhaust

4-2-1 Custom headers: the 2 secondary pipes between the OEM 4 pipes and the catalytic converter, are resized to 48mm.

I want some extra hp & torque, so in the near future I 'm planning to upgrade my valvetrain and after that I want to put the Toda A2 cams, with an obd2b to obd1 ECU conversion for the final tuning in the dyno. My goal is 180 – 185hp max. After that I want to make some adjustments in my transmission system (LSD and 4.7 final drive) for which I will go into detail in another post. But, before I move on to these modifications, I' m thinking to change my OEM ceramic catalyst converter first. The existing cat has never been changed because a metallic racing cat was too expensive back then. The basic idea is to buy a high flow cat (200 or 100cpsi), but I have the following questions:

1. To my knowledge, a high flow cat offers less resistance to the exhaust fumes when they come out. So, what about my back pressure? Is it possible to loose some torque in the low RPM?

2. Will this high flow cat lead to poor air/fuel mix? Is it necessary to change my ECU to obd1 in order to re-tune for better air/fuel ratio?

3.Will there be any significant change compare to my old ceramic cat? In other words, is it worth in terms of hp and torque gains?

4. 200 or 100 cpsi? Pros and cons.

5. Any reliable brand? I read that HJS is a good one. Kindly tell me your suggestions...

P.S.: Please excuse my rusty English :)

I m looking forward to read your valuable opinions.

Thanks in advance


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