effects of high flow converters on engine performance

[mwood1985]

how would removing the two main cats and replacing them with a magnaflow high flow on a 2001 4.0 affect the 02 sensors and engine performance? the final sensor is bettween the two main cats. i'd like to remove them to do a custom exhaust for better sound and performance while using a high flow to keep it legal and a flowmaster 40 with dual exits.

[triumphrider-1]

My assumption would be that it will lower low end power, but gain power higher in the rpm. Without dyno numbers comparing before and after though, I am not positive.

[mwood1985]

i know it will do that im more talking about it making the computer change the fuel mixture and timing an causing the moter to run badly

[triumphrider-1]

It shouldn't run poorly, and I am not sure if running a high-flow would throw a CEL or not.

[chazzone]

Catalytic converters seldom ever effect performance, especially on normal street engines. If you had a built/stroked v-8, you'd see a difference, but not with a stock 4.0

So, as long as you keep to the same size pipe, it shouldn't effect your performance at all.

Better flowing mufflers however, will make a difference, since stock mufflers can be restrictive, and a good performance muffler can increase flow.

Keep the O2 sensors in the stock location. One in front of the new cat, and one behind. The computer compares the signal to make sure the first cat is doing its job correctly, and if you take one out of the system, then it'll throw a code.

[mwood1985]

ive got a cat BEHIND the last o2 sensor if i delete that one and leave the first is it gonna pop codes?

[meatheaded nucklebuster]

as long as there is not an o2 behind it you can take it out but I doubt that is the case because all obd 2 vehicles have downstream o2 sensors to measure catalytic efficiency. If I were you I would skip the "high flow" cats and spend your money on a good sounding performance muffler that will actually give you a gain. Basically cats are not all that restrictive but even "performance" cats have to perform the function of reacting with unburnt hydrocarbons so that you dont throw a check engine light. So really the only good high flow cat is no cat at all. However, keep in mind that stock cats only are designed for a theoretical life of 100,000 miles before they start to be less reactive and then they will start to cause o2 sensor codes and poor gas mileage so depending on your trucks mileage you might want to replace them anyways. Just dont get suckered into some super expensive "high flow" model.

[chazzone]

Hi flow cats are cheap, about $65. Cheaper than any stock replacement. It might be a good idea to buy two, and put the 2nd O2 sensor behind the 2nd one, just to make sure it does a good enough job.