Stillen HFC vs. BERK HFC

BalanBro

I'm still wondering one thing, doesn't each bank have 2 cats (4 total for both banks?) The typical OBDII arangement was:

O2/AFR-->1st cat(usually in OEM manifold)--> 2nd O2/AFR-->2nd (downstream) cat

I was under the impression that the HFC replaces only the downstream cat (after the last sensor). So how would the sensor know whats going on further downstream? It should only be monitoring the upstream catalyst efficiency in theory.

Please tell me if I'm wrong here because I'm assuming this based on the late 90's OBDII cars I am familiar with.

wstar

I've never heard of 4 cats, but maybe on some weird vehicles...

Our car only has 1 cat per bank. The arrangement on our car is Exhaust Manifold -> Cat -> (rest of exhaust), and there's an O2/AFR sensor in the exhaust manifold, and another O2 sensor right after the cat. The one in the manifold is the expensive wideband one that the ECU uses to regulate AFR. The simpler O2 after the cat is just used to validate that the Cat is functioning properly.

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