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Adverse Affects of Gutting Cats

Broosedamoose

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What would be the adverse effects of gutting or removing the cats on a 4.0 SOHC engine? I ask only because my neighbor has a friend who just put a Magnaflow Cat-Back exhaust on his 2005 Ranger and had the cats gutted. Apart from being illegal and creating pollution, won't it affect the engine performance? Loss of back pressure, loss of low end torque, fuel economy, running rich/lean, etc.? He says it really improved the throttle response and pick up and hasn't noticed any cons of doing it. He also used some kind of O2 sensor adapter to take care of the CEL. It lifts the sensor up out of the exhaust flow. That alone must create problems with the PCM controlling the A/F mixture. I know this is a hot topic on here but I just want to make sure what I'm saying is correct! Is there anything else am I overlooking?
 


fastpakr

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You don't need backpressure for much of anything. Having pipe diameter too large can have an effect on scavenging, but that's different.

The O2 sensors after the converter are there to determine if the converter is functional, not to dial in A/F mixture.

I'd leave the converter in place because it's not a significant restriction and because I'm a supporter of clean emissions wherever possible. But the issues related to its removal shouldn't cause performance problems.
 

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Aside from being illegal in all 50 states on a federal level.......... on pretty much anything OBD-2, it will probably throw a code for the post cat O2 sensor and that will affect a variety of things.

I guess I'd imagine if there was a performance difference, the cat he had on there was probably plugged up. I have driven several trucks before and after cat deletes and have not noticed any difference, and they all had functional converters prior to that.
 

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cats are so smooth flowing nowdays it wouldn't be noticeable to gut them. i have done it a few times and noticed no difference. not specifically to rangers, just other vehicles i had that i was already doing exhaust work so i figured i would try gutting the cats. it made no difference in the running on those vehicles
 

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It is my understanding that when you gut a cat, the open chamber interrupts the flow of exhaust and can result in reversion. This can have a tendency to act as a flow restriction but may only happen at various RPMs. Cutting the cat off and replacing with a pipe would be better, but still illegal.
 

Josh B

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I believe it is also more prone to allowing sparks to blow through and out the exhaust pipe, which could lead to a fire on your tail if you're offroading, and if the officer writing you up has singed his uniform while chasing you be expecting extra tickets
 

Ranger850

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Can some one explain "scavenging" and "reversion" to me, I'm slow.
 

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Scavenging;
Imagine the exhaust pulses as waves. The top is high pressure and the bottom is low. When the waves hit an obstruction a reflection is formed going the opposite direction towards the valve (reversion). Where tube diameter changes diameter is an "obstruction ". Now if you can time the reversed low pressure pulse to hit the back of the valve as the exhaust is opening it makes it easier for the exhaust to escape. This only works at certain rpms. The manufacturer has done this to work for the average consumers driving habits. If you want to race then headers and bigger collectors of the correct length are used to tune to the rpm you want.
 

Blmpkn

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Ummmmm adverse affects?

Is stealing the childhoods, hopes and dreams of Scandinavian children considered adverse?
 

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Unless your Ranger is not registered for street use, trying to get it to pass smog could be an issue. Even if it passes the tail pipe check, they do a visual check for emissions equipment.
 

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One of the adverse effects is getting your post deleted… bottom line is that it’s illegal on ALL street driven vehicles in the US, even if you don’t have emissions testing in your area.
 

Josh B

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They had testing in Nashville/Davidson County, but my 80 Chevy LUV was manufactured without a cat.
I don't remember much of the details but believe it should have passed excepting I think they flunked it because it simply didn't have one.

I'd go once a year to a neighboring county, pick out an old house that looked like a quiet older couple lived there and use the address. After 2 or 3 years of this they built me a brand new 4 lane to drive over there on :D
I wonder if that old couple were getting multiple renewal notices each year ;)
 

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Its probably running in open loop permanently due to the sensor delete.

No cats is for carbs. EFI doesn't like it.
 

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