Hi everybody. I’ve been thinking about going through with the cat removal project and straight piping my ‘91 240, but I’ve got a few things I think I need to understand before I decide. If I straight pipe the car, am I understanding correctly that the car is gonna run LOUDER? Should I replace the cat with some type of muffler instead?

Also, I have what looks like the original cat which has the O2 sensor mounted into the front side of it. What should I do with the O2 sensor? Surely I can’t just disconnect it, right?

On the other hand, what about a high flow catalytic converter? Is there such a thing and does anyone have any recommendations? I should say that my reason for wanting to make some modifications has to do with the fact that the last road trip I took only produced about 21 mpg highway running about 75 to 78 mph. I get 20 mpg around town and thought I should get at least 24 to 25 on the road. The car has good plugs and wires, a K&N air filter and I run sea foam regularly. So, I thought removing the cat might help my fuel economy. Was I just pushing the car too hard or what? I appreciate your thoughts.

 

My muffler just came apart on a cross country road trip. It is certainly LOUDER than it used to be. I got close to 30 mpg all the way on the trip, with and without the muffler.

 

Other than it's illegal to run without the cat, ($500 in Florida I if I recall) it's a gamble if the computer will still run right. you could end up running worst. to my knowledge there are no aftermarket high performance as the FEDS run the program. Cat back systems are available and will give you some added horsepower.

Engine temp, a sticky brake caliper, plugs, wires, dirty TB, tires brand and pressure, filters, even having the windows rolled down all can effect millage to the tune of 2 or 3 mpg.

 

The illegal part is true and a high flow cat only come out for OBD II or cars after 96....I could be wrong or they might have universal, you were thinking cut the cat and weld on flanges to make it easy connections when it comes time for the smog?

 

Ok, lets say theoretically I removed the cat on my 240 and gained about about 2 mpg. I left the o2 sensor unplugged and have not had any problems in 600 miles. It was a very simple task a 2x14 inch pipe did the trick with two sleeves and two clamps. It is not louder it makes it sound a bit deeper but your car's exhaust is going to smell like a 66 ford. Next to go is the mid muffler.

 

I bought an aftermarket "high flow" cat off of the internet. It is a Magnaflow. They recommended a 2 and 1/4" cat but I went with a 2 and 1/2" cat. But I have also been told that they are all high flow. It was not cheap to get the thing welded in though.

You probably won't get the best mileage at 75 mph.

You could always just gut the cat, that is knock the honeycomb out of it. I don't know how easy that is to do. Also do you have emission standards to pass?

BTW, my car is an '84 242 GLT (turbo).

 

I know this is an old thread ... but maybe some input will help future deranged DIY car owners.

if your O2 sensor comes before your cat as far as exhaust flows, your computer receives no input from a faulty cat (Assuming your vehicle has only one O2 sensor). so there is no reason to suspect it responsible for poor fuel mileage. lower. back pressure is possible,but most likely not to blame. the fuel delivery system and emission system are highly advanced for their time. in this scenario maybe a cold start injector is stuck open .... Anyhow
use your heads.

 

My apologies for not posting back. I did in fact remove the cat and straight pipe the car. I did it a week or so after originating this thread. The muffler shop simply created a hole and threaded the O2 sensor in just in front of the weld. The car ran just as well after the cat’s removal as it did before. I didn’t bother checking the fuel mileage, nor could I notice any increase in power. There may have been an increase, but it was nothing I could detect, and I wasn’t gonna have the car tested. The only thing I noticed was an increase in the “hum” of the exhaust. It seemed louder to me than it actually was I think only because I wasn’t used to it. No problems in performance at all though.

Oh, and no more emissions testing in Florida and you will smell the exhaust more .