Catalytic convertor without emissions/smog equipement??

[zonacats]

Hello,

First time poster here, but I’m been lurking for a while now. I recently acquired an 84 K5 and I just put in a brand new GM crate 350. The mechanic took out almost all of the emissions equipment to make it as simple as possible for a weekend warrior/trail rig. After he put the engine in, he strongly suggested I have some work done on the exhaust. Specifically he said that the Cat was old and clogged preventing him from getting the most out of my new engine.

Today I called the exhaust shop and asked about getting a new Cat installed. They guy there said that since all the emissions stuff was taken out he said I would be wasting my money on a new Cat because it would just be ruined in short order anyway (due to the lack of other emission controls)... Does anybody have any experience with this set-up?

No (very little) emissions left on the engine, but keeping the Cat?

* also, there are zero emissions requirements where I live (not even visual inspection), but I still like the idea of a Cat to keep some of the drivability around town.

Thanks!

 

[badmix]

I have a 84 K5. I took all the emissions stuff off, blocked off EGR, yanked smog pump and plugged most of the charcoal cannister ports, only leaving the ones for fuel tank. Im running true duals (full length headers, Catco Cats and Dynamax). It gives a nice rumble and not raspy. Ive had this setup for 8 years, never a problem.

 

[shady]

if he'll do the job without installing cats just do it. theres no need for them.

 

[nsxxtreme]

Removing the cat if you don't need it will free up some power. You dont need them.

However installing a cat with the rest of the emission stuff removed wont harm the cat either. I would purchase a hi-flow cat off ebay for $40. Personally the power gains from removing the cat are minimal and I like at least cleaning the exhaust up the best you can.

I have all the emission crap yanked from mine including the EGR. I do have a cat and I can pass a sniff test just fine.

 

[zonacats]

Thanks all for the replys. Just want to say that even though I dont have a full membership (yet), this site has been extremely helpfull in diagnosing several small issues I have run into.

 

[rebelgregory]

To answer your original question, the factory cats on these used an air pump blowing into the exhaust to help the huge, inefficient, bead-filled, and inefficient OE cats complete the chemical reactions needed to reduce emissions. The newer ones, the honeycomb style especially, are smaller, lighter, much more efficient and require no added air. Therefore, if you want them, you can get them.

That said, everyone else here is correct. You don't need em. Cars ran all the way up to the late 70s without em. Lots of people (including me) have removed all the smog stuff with no problems.

 

[80' 427]

Power gains on the new converters are small. Power gained from the removal of the old pellet type converters it quite a bit esp if the pipe size is also increased.

 

[Teck]

The big benefit form running them will be the smell won't kill you if you run with the window down.

 

[zonacats]

See, that was my biggest concern. Granted, its not a daily driver, and will just be for fun, I would still like to minimize the fumes if I can. However, I realize that keeping the emissions stuff on the engine in tack would have helped that as well. I think Ill have him weld in the delete pipe for $40 and if im not happy ill purchase an aftermarket cat at a later time. Again, thanks for the advice!

 

[80' 427]

Switch to propane, smell is way less toxic.

 

[Blue85]

The AIR pump is outdated tech. With a new cat you don't need it. It can make some annoying popping/gurgling sounds and there are a lot of parts to that system that can go bad (check valves, diverter valve, pump, hoses, etc.). Plus, there's all that underhood clutter.

I have run with all factory smog equipment, with no cat at all and with cats on dual exhaust. Running the cat certainly makes for a better smelling truck. It also drops the noise level quite a bit. I just buy cheap universal cats - since I run two they don't have to be super-high-flow models. There are no smog checks here, I just run them for the sake of others behind me on a trail and so I can run with the back window down sometimes.

For the ultimate monster sound the cat is working against you.

 

[Deuling]

When i buy a vehicle. Step 1= hack the cat off. You know if its original its gonna have junk in it restricting flow. I run my tailpipes out the side behind the rear wheels, idling, driving, i dont smell fumes, and i run my tailgate window down, and open my slider windows on the top all summer long when its not raining. No problems here. If you run the tailpipes straight back or dump underneath i hear it will get sucked in.

 

[80' 427]

When i buy a vehicle. Step 1= hack the cat off. You know if its original its gonna have junk in it restricting flow. I run my tailpipes out the side behind the rear wheels, idling, driving, i dont smell fumes, and i run my tailgate window down, and open my slider windows on the top all summer long when its not raining. No problems here. If you run the tailpipes straight back or dump underneath i hear it will get sucked in.

Tailpipes? mine all go, Header, pipe to get it past the cab, longest glass pack I can buy, dump. Though some day the K30 will get a single 3.5 since I still have this huge megaflow left from when I thought it needed a turbo.

 

[Deuling]

In a pick its different cuz of no window. In a k5 the air from under actually swings up and in through the rear window when down. I know because when my tcase seal blew my whole tailgate and window were covered in atf spatter, all the way up the window too....

 

[K85 Octane]

Running the cat certainly makes for a better smelling truck.... I just run them for the sake of others behind me on a trail and so I can run with the back window down sometimes.

This^^ and that includes streets, freeways, and overall traffic conditions.
I don't get a say here about smog equipment, but even if I did, the cat would remain. I can be against tree-huggers AND give a damn at the same time.

 

[MrSchaeferPants]

Glad I read this. I wasn't sure why I was dying from fumes on my trip last weekend with my tailgate window down. I mean, I knew it was because the window down (half the trip, till I stopped to roll it up) but I was thinking it wasn't like that for all the older K5s with no factory cat, was it? I was wondering if I was just running rich.

Is the air stream the same with the topper off?

 

[shady]

it might make it smell better but if you can smell it it can poison you. taking the smell away wont stop that from happening. I've had CO poisoning, Its not fun. I'd rather know when it was getting in the truck so I could do something about it.

Plus I took my cat out of my burb and my exhaust dumps under the truck in front of the axle. Never smelled anything at a light or in traffic

 

[Blue85]

I run my tailpipes out the side behind the rear wheels, idling, driving, i dont smell fumes, and i run my tailgate window down, and open my slider windows on the top all summer long when its not raining. No problems here. If you run the tailpipes straight back or dump underneath i hear it will get sucked in.

This has been discussed multiple times. Pretty much every K5 here has had the tailpipes behind the rear wheels at some point and it is sometimes still a problem, so results may vary.

As for CO poisoning, I'm not very worried about it at highway speeds. I don't think having the smell creep through the floor with the fumes is going to be a safety feature either.