Are there any benefits to cutting out my catalytic converter?


#1

Hello everyone! I have a 1989 Buick Riviera and I am seriously thinking about cutting out my catalytic converter. I was wondering if I would notice any improvements on power or fuel economy?


#2

Why is it,plugged up ? You would probably notice little difference if it is open ,the only gain in fuel economy would result from the engine not having to work quite as hard to pump out the exhaust gases ,if its plugged up ,personally I would recommend a free flowing replacement ,back in the day cheapskates would run leaded gas through the cars equipped with converters and plug them up .If you live in an area with emission checks this may cause more harm to your wallet then benefit.


#3

Be aware that it is illegal to remove emissions equipment such as catalytic converters. If your state has a safety and emissions inspection you will fail automatically and, depending on the vindictiveness of the inspector, you could get reported to the EPA. IMHO it is not worth any performance or fuel economy gain for such risks.


#4

By 1989 they had cats pretty well figured out. I don’t think you’d see any benefit.


#5

O2 sensors??? If so then cutting out the cat will GIVE YOU DRIVABILITY problems.


#6

@MikeInNH You can get MIL eliminators to fix that problem. Though just replacing the cat with new one (assuming it’s plugged it) would be easier, the OP can get a new cat for less that $100 for that particular car, probably around $200ish total once labor is figured in.


#7

This OP had a recent thread asking how to increase their auto repair business. A question like this might explain why they need help increasing the business.


#8

Volvo, why do you keep looking for faults with the OPs?


#9

A 1989 car doesn’t have OBDII or a downstream O2 sensor, so there’s no place for a MIL eliminator.
The engine computer doesn’t test the converter.


#10

@circuitsmith good catch, I overlooked that bit of key information


#11

In a word no, and its illegal.


#12

I did a lot of removing or gutting cats back in the mid to late ~70s, when they first showed up. It was always accompanied with drilling out the carburetor’s main jets to pre-1975 diameters, restoring engine base timing (and if possible timing curves) to pre1975 specs, and disabling the EGR.

We even did some of these things on brand new cars in the dealership when we were “new-car-prep’ing them”.

The result was always a very noticable increase in gas mileage, power, and driveability.

However, the OP has a 1989 vehicle. Removing the cat alone will likely not buy much in the way of power or mpg. Unless it’s plugged, I suspect it won’t even be noticed.


#13

A new cat is only abut $100 and I had to replace mine. It hadn’t failed, just rusted off. But if you need more power than the fuel injected 3800 will provide, there is something else wrong. That car wouldn’t take a back seat to many others on the road.


#14

You might notice some improvement in power if your current cat is partially clogged. I wouldn’t expect much improvement in fuel economy though. As mentioned above, if you live in the USA you risk violating Federal law messing with the cat. So if you do it, don’t get caught, as the fine may be considerable. Likewise, there could be a problem with the engine computer with no cat. What it would be, you’d have to remove to cat to find out. You may end up with a check engine light on all the time, which will prevent you from knowing when there is some other problem developing.

One idea, have the current cat’s back pressure tested. The shop will usually remove the pre-cat O2 sensor and plug in an instrument that measure the pre-cat exhaust back pressure. If that measures ok, then your cat isn’t clogged, so removing it won’t do anything at all other than spoiling a warm afternoon by needlessly wrenching under the car.


#15

If it isn’t plugged up it would just be a waste of money and time to eliminate it. You won’t notice any difference if you remove it.


#16

There’s only one O2 sensor on it before the cat so the computer isn’t going to know but its a bad idea anyway.


#17

You must belong to the fraternity of the infernal machine the more racket.the more power.I see way too many Dodge pickups with Cummins diesels(already plenty powerful ) with the exhaust system removed ,why I do not know ,I know this I drove a truck once that gained a lot of power when you rolled the passenger side window down(you could hear the racket better then - had a powerful roar ) .
John Ligenfelters book mon small block chevys goes a long ways in discussing whats appropiate and cost effective on exhaust systems ,foe some reason some of these newer cars need a bit of backpressure to function correctly .


#18

I’m not sure if it’s backpressure per se that is needed. We observe an engine making more power with a muffler and we assume it’s backpressure that’s causing this effect. But a muffler also dampens acoustic energy and kills the standing waves that interfere with gas flow at certain rpms.
A pressure pulse travels down the pipe and when it reaches the end, it reflects a vacuum pulse which is reflected as a vacuum pulse when it hits the closed exhaust valve and then is re-reflected as a pressure pulse. If you terminate the pipe with a series of small holes, then there no longer is a well defined point where the pipe suddenly ends and you get less notching and the engine does not have dead spots at rpms where strong standing waves form in the exhaust.


#19

“a vacuum pulse when it hits the closed exhaust valve and then is re-reflected as a pressure pulse”

Actually, a wave reflected at a closed pipe is not inverted.
Otherwise, I agree with the rest.
There are conditions when the rarefaction (vacuum) wave will reach an open exhaust valve, which enhances engine output.
This can be useful in a circle track racing engine that stays in a narrow range of rpm.
In a street car you don’t want a series of hills and valleys in the torque curve.


#20

wAAAY back when . . when leaded gas was still a choice at the pumps . . You could buy the cheaper , or you could buy whatever , and not worry about the cat.
if you are constantly out in the sticks and brush fire is a real worry . . then sure, cut away ( or hollow it out. )