Harv69

A friend of mine is thinking about purchasing a 81. The car is in excellent shape and has 70000 miles on it. The only thing that is missing is the catalytic converter. It looks like it was removed sometime ago and replaced with a piece of pipe.....Will this effect how the engine runs? (other than the increased emissions)

77Dream

Yes it will... there will be a little better performance. :thumbs:

BSeery

:withstupid:

The 1981 is a computer controlled car, so any mixture problems that would come up from removing the converter should be taken care of by the computer and O2 sensor.

Tom73

But the 81 is a computer controlled carburated car, so it ability to adjust mixture problems would not be near as good as a fuel injected car.

Personaly I would stay away from the 81 because of the computer. But that is a personal preference. :)

tom...

81' Corvette Guy

Come on now..not so hard on us...we love our cars too!!! :nono:

hunt4cleanair

Apparently the previous owner figured out how to make it run without the cat but if your friend wishes to return to stock configuration, he should ask what other emission control devices were removed...and specifically those removed to avoid "CHECK ENGINE SOON" warning light. I'm looking at an 81 computer command control manual but don't see any devices that would affect performance without the cat but again...other devices could have been removed and carburation modified to compensate. I don't think you could replace proms like you can today in 81...again the first year with the exception of the LG4 California cars in 80.

In 82 the cat converter had a tube from the AIR pump that delivered oxygen to further burn unburned hydrocarbons while also having an electronic lead for feedback back to the computer. I don't believe any of this was in place for 81 so he may be fortunate there.

Keep us posted on your findings.

Boofers

Not that I know from personal experience but some people say that without cats your exhaust smells really bad and your garage will end up smelling like sulpher and gasoline.

twan

Is the test pipe welded into place or bolted up with flanges?

I been meaning to cut both of mine out (full dual exh) and welding flanges on the cat(s) and the test pipe(s) for fun all around, and inspection purposes later
=)

Gator81

The straight answer is given above: Yes, it will run better.

The more important answer is also given above: Depends on whether the cat is the only thing removed.

Most of the time, in my experience, when Bubba pulls off the cat, he doesn't stop screwing with the car. The air pump is usually next; and that's not so bad. As you say, other than emissions, removing the cat and air pump (they work together) usually just increases power.

As long as the computer, carb, HEI distributor, vacuum sensor, EGR, and (critical!!!) O2 sensor have not been screwed with, things will run just fine. The O2 sensor is the main feedback mechanism that allows the computer to adjust the air/fuel mixture in the carb.

Personally, I get really tired of the :bs ideas some people have about how the '81 with the computer is some kind of black box full of snakes that can only make 190 horsepower unless you remove everthing not invented before 1969. Mine is well over 300 hp and is completely smog legal, still using every emissions device including the cat and air pump. There are many ZZ4 '81's out there with more power than mine, including some on this forum, and most of them are smog-legal. My '81 will pass the tailpipe sniffer test as clean or cleaner than the L81 stock motor did, and all of the emissions equipment is in place and working. Yes, I installed an aftermarket chip in the computer (Hypertech).

But the key is this: The computer DOES NOT control the entire carb all the time. It only controls the mixture on the primaries when the throttle is about 2/3 open or less. It doesn't control the secondaries at all. Nothing, zip, nada. If the throttle is open far enough for the secondaries to open, just as in any Q-jet, then the computer is bypassed and the performance of the carb is limited only by your ability to tune the metering rods. In effect, it becomes a mechanical carb.

The second main function of the computer is to control the spark advance, as there is no vacuum advance. This is where the aftermarket chip comes into play, as it can give you an advanced spark curve. In my case, I have more compression than stock, and always run 91 octane fuel, so I can use more advance and a cooler thermostat to make more power. The aftermarket chip helps with that, although a completely custom chip could probably improve on that somewhat.

It boils down to this: If your friend lives where the car will have to pass emissions, and all that's missing is the cat, then putting a cat on the car is not a big deal. A new PFP or Random Technologies cat will be only slightly more restrictive than that "pipe", and it'll be clean. If the emissions test is irrelevant, and all that's missing is the cat and/or air pump, then no problem. :seeya

Dalannex

Gator has it right on the money. If the cat is the only thing removed, and the rest of the smog equipment is there, and hasn't been tampered with, AND he has to pass emissions, I would just throw a high flow cat on it and be happy. Now, if he lived where I do and was me, look at my sig.... :cool: Mine is not stock, not a real hot rod, but not stock and I am running all of the stock fuel/spark/computer setup. I even have the smog pump on mine, even though i don't need it because the converter is gone, it makes it look pretty stock. The computer controlled carb has no limitations that any other q-jet doesn't have. They are essentially the same carb, it's just that the computer controlled (E4ME) carb is far better at metering fuel IMO. The E4ME can be tuned for more HP quite easily if you know the procedures. And, the best part is that there are a few of us right here on the forum that can give any help needed should a problem arise. We've been through it. :thumbs:

-Justin

Harv69

Thanks guys, I've looked it over and it appears all the other emissions stuff is in place. Including the air pump. However there is a black hose running off the air pump toward the rear of the car. This hose stops about halfway across the engine compartment and has a plug in the end. I assume this hose is suppose run all the way to catalytic converter, to add extra oxygen.

Harv69

Also the pipe in place is bolted in and looks older and rusty compared to the rest of the exhaust (which appears to be relatively new) so the converter has apparently been gone for along time.

Gator81

Harv,
On a stock '81, there's a hose from the air pump (as you saw) that goes over to the passenger side of the engine, where it ends with a check valve (a one-way flow device); the check valve goes into a steel line, about 1/2" or maybe 5/8", which goes to the cat to provide extra air (as you correctly guessed).

I would suppose that piece of pipe that's in place of the stock cat is what used to be called a "test pipe", and it's made of plain steel. The original exhaust pipes are a variety of stainless steel, which tends to take on a bit of a rusty appearance but never really corrodes. That would explain why the short pipe is newer than the exhaust system, but looks much older. Plain steel will go from shiny to ugly-rusty in just a few months when subjected to exhaust temperatures.

Dalannex

That's right, the hose is for the steel line that used to run to the converter to add air. Mine still has that line, in perfect working order, only it runs down to the passenger side tailpipe and is welded in there. So I get a little extra air in that one I guess. :lol: The true duals were done before I got the car, all I did is add the flowmasters to it.

-Justin

DaveL82

Remeber, when this car was new the catalytic converter technology was still new. Since then most of today's cars run cats without any problems. The old GM cats as used on the 81 were the worse since then were a pellet type. If you need one for emissions it's simple to add and will not hurt performance.

People that claims cats hurt performance are living in the past. The new ones are not the problem, it's the 2 inch single exhaust.

Just us it as a negotiation point.

Have fun.