Cats

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F152702951830

So, found the internals of the catalyst are rattling. Trucks a 200k 1995 Silverado. I dont have to pass emissions with this one in my county.

Im cheap. 

The options i see that are financially viable: above linked cheap  "high flow" cat (or something similar price)

Hollow the current cat with a chunk of pipe.

I actually do care about the environment, and being technically legal. However, theres much bigger fish to fry here at this point. 

What effect does a hollow cat have? Is there a negative other than emissions and illegality in an obd1 car with no downstream o2?

Is a cheap cat worth the expense and hassle of installation?

If it gives you a warm fuzzy, put a replacement cat on it.  If you don't give a E36 M3 and are short on money, gut the thing and drive on.

In reply to Dusterbd13 :

I would put a cat on it. They really stink without them. 

I put two cheap high flow cats from summit in my 1986 GMC Sierra when I put headers on it and ran true duels. It always passed the etest we had in Ohio at the time.

my last cat was a no name(magna?)  from O'Reillys 3"in 3"out to work with my 3" gibson catback, less than $90 a few years ago......could see day light thru it

I've run these "fake" catalytic converters on two vehicles. 

click here- 40 bucks !

Where I am in Texas, even if I don't have to pass emissions due to the vehicle being >25 years old, I still have to pass a visual for the converter. These fill the bill.

I'm with Nick. They stink without cats. Put a cheap one on, enjoy.

Nick Comstock said:

In reply to Dusterbd13 :

I would put a cat on it. They really stink without them. 

I put two cheap high flow cats from summit in my 1986 GMC Sierra when I put headers on it and ran true duels. It always passed the etest we had in Ohio at the time.

That's where I'm at too. I don't get off on the raw fuel smell like some people do.

I'm considering putting a tiny one on my Mini, when I get around to getting it back on the road, just to keep the stink at bay. I don't have to, on a 58 year old car, in Wisconsin, though. 

I out a good Walker catalyst  on my Firebird a couple years ago. Wasn't much more than $100 on E-bay for a 3" in and out. Car ran better with it than the el-cheapo it replaced.

 Running no cat on a obd 2 car will probably trip a check engine light, but run fine.

My RX7 with out the cat and the fuel trim set for the track would make your eyes water. 

So if you are looking for cheap catalysts- if you can find any with reviews, I'd avoid at all costs any that have a large amount of physical failures- where the brick gets loose and starts breaking apart on it's own.

The other part that makes them cheap is lack of precious metals on them- platinum, palladium, and rhodium cost a lot of money.  What you will see with that is lower overall performance, where you will likely smell it during a cold start.   Otherwise, they should perform well enough so that you can't smell it, nor should you get a CO headache.

Since we can get some really good details from manufacturers of catalysts, I really wish that the aftermarket would do the same.  That way, it's a lot easier to give you good information of what you are buying.

In reply to alfadriver :

Depending on the exhaust layout, a cheap cat can sometimes be moved further forward to get it lit off faster.  I ended up doing this on the Jeep (moved the cat from behind the crossmember to in front of it) to make space for a second muffler.  End result was that it took less time to stop smelling on a cold start than the stock cat did. 

In reply to rslifkin :

I had mine directly after the collectors if my long tube headers. I was concerned that with the headers bleeding heat as they do the cats wouldn't light off. I never noticed any issues and it always passed the roller tests. 

However, I put the same cats on my 1976 Cutlass but had to mount them father back from the headers and although that car never got tested the cats were certainly less effective based solely on the smell. That car had a cam and head work and a much bigger carb where the truck engine was mostly stock. 

rslifkin said:

In reply to alfadriver :

Depending on the exhaust layout, a cheap cat can sometimes be moved further forward to get it lit off faster.  I ended up doing this on the Jeep (moved the cat from behind the crossmember to in front of it) to make space for a second muffler.  End result was that it took less time to stop smelling on a cold start than the stock cat did. 

But the risk of that is that you will over temp them and damage them.  It's a conundrum that OEMs have to face- light off time vs. temperature durability (and all that ends up meaning).

I think you'll find that the check engine light gets annoying.  Plus, with it always on, you'll never know when something actually goes wrong.

The upstream O2 sensors are used for engine control.  The downstream sensors monitor that the cats are doing their job.  No catalyst = check engine light.

The fix is to use O2 simulators in the downstream bungs.  They feed a consistent fake signal to the computer to make them think its working right.  But, until you invest in two simulating sensors I think you'll find that just replacing the cats with cheapies does the trick the "right" way for about the same money.  You can also pay to have someone reprogram the computer to ignore the downstream sensors, but again... probably costs the same or more.  Most respected programmers (especially ones who are willing to break an unenforced law) won't open up a laptop for less than $250

Universal hi-flow cats are what... $80 each?  I'm also a bit of a tree-hugger, so I do have to point out that cats really do amazing things for the air we all breathe.  I wouldn't judge you for not using them, but doing the job right in this case isn't much more money.

I'm putting a 550-hp LS1 in a 1967 car.  I'll be putting cats in.  I will likely not do downstream O2 sensors since they aren't needed, but the cats don't really cost any hp and as long as I have the sophisticated engine controls to make a catalyst work properly I'll use them.

In reply to alfadriver :

How much of a concern would that be when we're still talking about cats behind the mid-length headers and y-pipe?  I'd expect it's not an issue considering how many newer OEM installs put the cats a heck of a lot closer than that. 

Curtis said:

I think you'll find that the check engine light gets annoying.  Plus, with it always on, you'll never know when something actually goes wrong.

The upstream O2 sensors are used for engine control.  The downstream sensors monitor that the cats are doing their job.  No catalyst = check engine light.

The fix is to use O2 simulators in the downstream bungs.  They feed a consistent fake signal to the computer to make them think its working right.  But, until you invest in two simulating sensors I think you'll find that just replacing the cats with cheapies does the trick the "right" way for about the same money.  You can also pay to have someone reprogram the computer to ignore the downstream sensors, but again... probably costs the same or more.  Most respected programmers (especially ones who are willing to break an unenforced law) won't open up a laptop for less than $250

Universal hi-flow cats are what... $80 each?  I'm also a bit of a tree-hugger, so I do have to point out that cats really do amazing things for the air we all breathe.  I wouldn't judge you for not using them, but doing the job right in this case isn't much more money.

I'm putting a 550-hp LS1 in a 1967 car.  I'll be putting cats in.  I will likely not do downstream O2 sensors since they aren't needed, but the cats don't really cost any hp and as long as I have the sophisticated engine controls to make a catalyst work properly I'll use them.

I hate to correct you, but the downstream sensor IS used for fuel control.  Has been for at least 20 years.

So we all know.

The need for a second O2 sensor for fuel control is very based on what your controller is- mostly OEM or not.  If not, without some good instruments and testing, it's not something most can calibrate to work really well.  So for this board, swaps are unlikely to need or use the second O2 sensor- that i'm fully in agreement with.

And for this truck, a 1995, it's not likely to be all that helpful.

But from an OEM standpoint, the rear sensor is a pretty key control part.  It's pretty amazing what it can do.

rslifkin said:

In reply to alfadriver :

How much of a concern would that be when we're still talking about cats behind the mid-length headers and y-pipe?  I'd expect it's not an issue considering how many newer OEM installs put the cats a heck of a lot closer than that. 

Depends on the header.  I've seen some "Hooker" headers for a 5.0l that are easily short enough to cause catalyst problems.  But, generally, you are right that most headers are long enough to not be the problem that we deal with.