High Flow Cat question. - PeachParts Mercedes-Benz Forum

davidmash · #1 04-08-2010, 11:30 PM

I was helping a friend change out his exhaust and he purchased a new stainless steel headers wit what he was told are high flow cats. When I look down the pipe I see a hollow tube. The part that supposedly has the cat in it has a thicker wall with perforations in it but I can stick my arm down the pipe with no obstructions. I remember seeing the inside of my cat when it was replaced and there was a honeycomb like material in it with tiny holes lined up parallel to the air flow.

Is what my friend has a high flow cat? I don't see how this can work as most of the exhaust passing through the pipe will not come into contact with any surface area so how does it break down the pollutants in the exhaust?

davidmash · #2 04-08-2010, 11:32 PM

OK, I may have just answered my question but I still do not know how it works. What he has looks like this:

I do not understand how something like this cleans the exhaust.

Chas H · #3 04-08-2010, 11:35 PM

Quote:

Originally Posted by davidmash

I do not understand how something like this cleans the exhaust.

It doesn't clean the exhaust, it flows well.
If your friend's car is subject to an emission test, it will likely fail.

t walgamuth · #4 04-09-2010, 06:50 AM

That is false advertising. A cat is worth quite a bit of money. I'd return them or try to get a refund. OTOH if he had to cut his old system off and needs the car back on the road he may be kindof in a pickle. Threat of reporting them to epa might get action.

raymr · #5 04-09-2010, 08:38 AM

Its designed to LOOK like a cat, but an exhaust test will uncover the truth.

Ara T. · #6 04-09-2010, 08:40 AM

Does Texas do emissions test or just visual inspection? If the former, he's probably hosed.

Jim B. · #7 04-09-2010, 10:13 AM

That thing WILL pass the VISUAL inspection, which is the point of buying one of them.

They are flagrantly illegal, unless for "off road use only" and not to be used on the street.

But if the smog technician bangs on it with a rubber ended mallet, the car owner is doomed, and the jig is up.

But most smog techs don't, and Mercedes Benz cars running nice and hot and all warmed up, and in good tune, have a reputation for burning clean, so with one of those on a car in that condition, might pass even a California smog test, if the visual is glossed over, even in a very strict (San Francisco or Los Angeles basin) California area

pj67coll · #8 04-09-2010, 10:57 AM

You'd fail in Phoenix. They stick a reciever over the tail pipe and rev the hell out of your engine and sample the exhaust. That contraption doesn't clean anything so it would fail here.

- Peter.

Pooka · #9 04-09-2010, 01:13 PM

Cats work on the principal that they get VERY hot and as the exhaust gas passes through them the unburned hydrocarbons are burned. If the media inside is hot enough it could, in theory, ignite the unburned hydrocarbons.

Given your location (Dallas County) the car will be subject to an exhaust inspecton. Why not drop by someplace that does inspections and ask them what they think of these things? I am sure they have seen them before.

rwthomas1 · #10 04-09-2010, 10:46 PM

I have seen many hotrods without cats, or gutted cats, pass emissions tests easily. It is dependent on the tune of the engine, how hot it is, etc. The other trick is a methanol mix in the gas tank to get through the test..... Those cats may or may not be legal, depends on the laws and the application. RT

DieselPaul · #11 04-09-2010, 11:45 PM

As stated, it doesn't look like it will filter well, because it won't. It is for horsepower, not emissions. MAYBE it does something but it mostly is just for a visual inspection type thing.

C Sean Watts · #12 04-10-2010, 12:53 PM

Pass or fail of the inspection will depend on how old your 'friend's' car is, the state/local inspection regulations and how well the rest of the engine is tuned.

I was in Texas in '89 and then some counties did not emission test - now? I have no idea.

If the car is OBD1 (mostly pre 1996, it is relatively easy to make it work.) If it's OBD2, it requires a little more work. In most places in the country OBD2 cars do not get 'tailpipe tested' but the inspector will look at the MIL (check engine light) before and after engine start up.

See this

I've made a few of these, and they work.

Since 90% of the emission control happens UPstream of the cat. the engine should be tuned properly and the final tweaking that the cat. does will not even be a factor other than visual inspection.

davidmash · #13 04-11-2010, 01:06 AM

He has a 2006 Trail Blazer SS. Since with the emission test here they just hook his truck to a OBDII plug, if the car does not throw any codes, how would the machine know the emissions are bad?

He has a friend who is tuner and belongs to the local SS club. Several of them have high flow cats and said there is no issue. What you said about a tunes engine makes sense though. No way my car would pass. Two more years and I do not have to worry about it any more. She will be a 25 yr old classic and I am exempt.

kmaysob · #14 04-12-2010, 01:22 AM

here in phx if you are 96 and newer obd2 they do not smog your vehicle. they hook it up to the computer, look to see if the check engine light has been on and if all clear you pass.

4x4_Welder · #15 04-12-2010, 10:25 AM

You'll need a secondary O2s eliminator, they used to have them in the Summit racing catalog.
If those were advertised as catalytic converters, though, you need to report that company. Those are not cats, they are test pipes with shrouds. That sort of jackassery is what gives motorsports a bad name, and causes legislation like making it illegal to think about removing the cats.
FWIW, I had an F250 years back with a computer controlled carb and ignition, stock 351w, and a cat. It failed emissions horribly. I pulled that engine, disconnected the computer, and installed a very hotly built 300-6 with no cats and an old electronic ignition with mechanical and vacuum advance. Being an 84, they didn't do the mirror check to see if it had cats, just stuck the sniffer on and it passed amazingly well.
All a cat does is clean it up a bit, if the engine is running right in the first place they aren't needed.