OK...why did I cut a 40 lb chunk of metal out of my exhaust?

-Why was it there to begin with?

I can tell you why. It was there because a couple of years ago I paid $500 for a pair of 928S4 catalytic converters for my '85 928S2.

First of all, the 928S2 was not a car that Porsche ever officially imported to the United States. This particular car was sold from a dealership in Vienna Austria and shipped to the US in the spring of 1985- a "gray market" car. As such, it was built according to European regulations without catalytic converters.

I run every day that I can. As such, I appreciate clean air. When I bought the car in 1999, it had what looked like an aluminum sewer pipe for an exhaust- 4 inches wide and no catalytic converter, it terminated in a goofy looking cheap Pep-Boys muffler. It sounded great, and woke up everyone in Seminole county, Florida.

The problem? I live in Orange county! This setup was LOUD!

I promptly replaced this with a pair of Porsche cats and a Borla exhaust setup from 928 International. The sound was still loud but reasonable. And it didn't stink like an old school bus when I came to stoplights!

Well, this car always has had a problem with a slight miss during hard acceleration. I've gone over everything and still havent been able to solve this, though I'm bearing down on it I think. The car runs far better now than it did when I bought it, but not perfectly. Recently, people who work for a prominent drag racer [Connie Kalitta] examined this car and told me that they thought the problem was probably a plugged catalytic converter. For years the car ran way rich...so I decided to test the car with a vacuum gauge. Sure enough, it seems that one or both of my cats acts plugged up....

OK. I pulled the cats recently and replaced them with a test pipe. Supposedly this is worth nearly 30 hp on a 928 and let me tell you, they are correct: When I drove the car after affixing said test pipe [Ott Crossover it is called], it was night and day- suddenly there was all SORTS of power throughout the whole powerband. Yet... I could still feel that slight hesitation. I figured something out all right...just not the thing I wanted to "figure out"! The long and short is that it runs better, and there is almost no stink at all, probably attributable to my replacing nearly everything on the injection and ignition.

Well, I feel bad about pulling the cats off, and this is only a temporary situation. Or is it?

NUMEROUS California residents who own 928's report that despite the lack of catalytic converters...their cars PASS that state's stringent emmisions standards! Apparently, they remove the guts of the converter so that it appears that it is in place, yet the fact is that this is now nothing but a straight through pipe.

I was always taught that it was ESSENTIAL for emmisions for this part to be in place!

IF this is not necessary, then why is this expensive 40 lb part mounted under our cars?

What do catalytic converters do? Did I waste $500? For what it is worth, I examined the cats that I removed. They appeared intact, and when I poured water through them with a hose, it flowed through them perfectly, like there was nothing inside. Hmm.....

Normy!
'97 Aerostar 3.0
'85 928S2 5 Speed

 

You said your car ran rich for a long time. That is what ruined your cat. The cats don't actullay provide that much resistance. You can also get high flow cats, which are for racing. Do a search on the web for info about the cats, you will be amazed what you learn.

 

There are a couple of reasons. First, the auto manufacturers have to show that they meet emissions standards after X number of miles. Back in 1985, I'm guessing that it was around 50K. That number keeps creeping up and is on its way (if not already there) to 100K. New cars don't have problems, it's the ones that have higher mileage. Second, there's margin because of production variability. Some car are cleaner than others even though they came off the same line. So, the auto makers design for worst case.

I don't think the state emissions tests are a good indicator of the real world. Maybe they've changed, but when I lived in California (until 1996), it was just an idle test and a high speed (high idle) test. There was no load on the engine.

 

california now does smog tests at speed on rollers, similar to a dyno

while you're at it why don't you take off your bumpers-thats just unnessicary dead weight too

 

Iti is a political issues, like everything else emission-related. Costing customers a pretty penny. If in CA, and your car is old and doesn't pass emission, you have to get a new one.

same thing with Freon. Do you have any idea how much it costs to change to the new style refrig. in the *whole* country?

Billions.

 

The cat is there to clean up emissions from incomplete combustion. Indicating that if the engine is running properly the cats are unnecessary. I think Ford has a gas engine that has met CAs ZEV requirements. I thought it did it without cats but I might be wrong on that point.

If Mikeman is correct about the endurance emissions that could explain much. When cats first came out cars had carbs and were done by 100,000 miles. Now we have EFI and cars that don't need new plugs till 100,000 and can be expect to run twice that. My theory is that carbs wore out around 50-60K miles and started dumping excess fuel into the engine. If it was not serviced or replaced this excess fuel washed oil off the cylinder walls and caused the rings to wear, blow by to increase and the engine to wear out. With increased blow by the emissions would go up as well.

 

A car has catalytic converters? None of mine seem to have any. I wonder where they went?

 

the way I always understood it the cat is a sort of safety net.
when the car is tuned properly the cat isn't generally nessicary to keep emissions levels acceptable, but when the car drifts out of tune, it seriously reduces unburned HC emissions. this can actually make diagnosing a dead cylinder difficult, since a dead cylinder is dumping loads of HC out the exhaustpipe, but the exhaust sniffer doesn't see it cause the cat burns it up.I knew a couple mechanics back in the 80s who welded a plug in front of their cats for tuning purposes.

on another note I had a 74 Mustang II, the year before cats came out, and you couldn't see the engine for all the vacuum controlled emission stuff. the 75s were much simpler to work on, so in that case cats simplified things alot

 

A cat converter reduces emissions by burning off unburned hydrocarbons. These hydrocarbons, when introduced to a warm converter, cause a temperature rise in the catalyst material which burns off the hydrocarbons. Running rich therefore overheats a converter and plugs it as the core begins to melt down, and this was more pronounced in cars with carbs, especially when the choke stuck on or when there was a misfire condition (gee, guess why manufactures started using electronic ignition when converters first came out).

Todays computer managed fuel/ignition systems are pretty precise and therefore the converters last well beyond 100,000 miles unless.............there is a system malfunction. Also, for at least the last 15 years the converters have very little restriction, unlike the 1975 technology that used a pellet bed. Today, unless something changed, they are using a ceramic (probably) core impregnated with the catalyst materials and the last one I looked at was hundreds of small squares through which exhaust passed. Not much of a restriction at all. To inspect for plugging, put the garden hose away and hold the converter up to a bright light and look through it, observing for plugged passageways in the core.

BTW, a hammer and a long, solid steel rod make for easy removal of the core

 

Just because water runs through it does not mean anything. Mine looked like Stalingrad on the inside when I took it off. The ceramic stuff was all crumbled and ratting freely on the inside. At that state, my F250 maxed out at 35mph in 5th gear. It was that bad.

Sorry, can't afford a new one.