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To cat or, not to cat

BeaverMeat

BeaverMeat

Active member
Joined
Aug 8, 2020
Location
Vancouver Island
Wanting to install a high flow cat on my custom 5.0 swap exhaust. Anyone install cats in their 5.0 or LS swap and where is the optimum placement?

The car has headers that lead into a 2” Y-pipe into a 3” single all the way to the rear.

Is it best to use two spun cats on the 2” Y-pipe right behind the headers, or one cat on the 3” single after the y-pipes?


NOTE: I know all the rhetoric. “It adds weight” or “it reduces performance” yadda, yadda, yadda. It’s not 1985... for practical purposes I want my car to stink less...
 
I run 2x 2.5" cats on my 5.slow drift car. They are positioned to be just in front of the trans crossmember. I mounted them in this location to have increased ground clearance on a lowered car, and two 2.5" cats have more flow potential than a single 3". I mounted them with cheap v-bands. If they fail, I can easily swap them out or replace them with a straight section of tubing.

You could easily run a single 3" cat further back as well.
 
Yes, running a cat is always a good idea on a street car.

Just to argue with Bobbert, a single 3" would be cheaper and simpler.
 
culberro said:
I run 2x 2.5" cats on my 5.slow drift car. They are positioned to be just in front of the trans crossmember. I mounted them in this location to have increased ground clearance on a lowered car, and two 2.5" cats have more flow potential than a single 3". I mounted them with cheap v-bands. If they fail, I can easily swap them out or replace them with a straight section of tubing.

You could easily run a single 3" cat further back as well.
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Harlard said:
Yes, running a cat is always a good idea on a street car.

Just to argue with Bobbert, a single 3" would be cheaper and simpler.
Click to expand...

Good to know. Wasn’t too sure if a modern 3-way cat could be placed right after the header. I know if it’s placed closer to the heat source it helps with efficiency but, you run the risk of burning it up.

Having a singe after the Y may be cheaper... bobbert does have a good point about flow potential with having two.

Well... if there is anything worth doing, it worth doing rightz
 
Less combustion stench with the cats.

They’ll be slower to get going but will still be functional. Make some heat shields around them.
 
area of 3" is 2.25x the area of 2". So I would go with the 3" since it should flow more, it's simple, and it will light off eventually. Not ideal for hybrids, but you will have it cooking for longer periods of time.
 
blkaplan said:
This,

It's good to be considerate of everyone around you.
Click to expand...

Ursan said:
Run with a cat. Don't be that guy.
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It never had a cat for the last 17 years and he drove it in the summer only. Never noticed the smell until it got colder outside.


2turbotoys said:
You could always use a free flow cat like this, and it's only $40 in stainless steel

http://www.siliconeintakes.com/dsm-intercooler-piping/catalytic-converter-p-320.html

Properly tuned cars don't stink much more than factory cat cars
Click to expand...

That’s just a test pipe to “fool” da man.

The extent of tuning on this car is a OE 1989 5.0L with a 70mm throttle body, K&N filter, headers, and cat-less exhaust. That’s it. Crappy cams and all.

Stinks like any old 5.0L
 
I know what that is, was kind of a joke. Tune it then. Ever get behind an old carbureted car? That stinks. Most modern cars with a proper tune do not have that problem. You can not get a tune for that engine? If not, get a high flow cat.
 
2turbotoys said:
I know what that is, was kind of a joke. Tune it then. Ever get behind an old carbureted car? That stinks. Most modern cars with a proper tune do not have that problem. You can not get a tune for that engine? If not, get a high flow cat.
Click to expand...

I comes down to cash.

Column A: get a cat
Column B: get an ECU

Cost to value... the cat wins.
 
Here's a Magnaflow I had years ago. Super easy to place.


a-M.jpg



Cat%20003-M.jpg



Cat%20002-M.jpg



PB190013-M.jpg
 
BeaverMeat said:
It never had a cat for the last 17 years and he drove it in the summer only. Never noticed the smell until it got colder outside.
Click to expand...

Its not just smell. Your nose is not a full spectrum exhaust gas analyzer.

Yes its true,,, if your car is well-tuned you have less of a need for a cat but you are thinking mostly about steady-state cruising when the car is warm. Accel / decel + warmups are not clean.

You can pass a sniffer test with just a stead state load without a cat if the car is tuned well, but that same car on a dynamic dyno will quickly fail.
 
they don't really kill power either as long as they're sized reasonably and not clogged full of ****
 
I'll have to disagree with the idea that you can tune away hydrocarbons. I can smell any vehicle with no cat. I worked for Datsun in the late 70s and early 80s, and we had cars with and without. The ones without a cat definitely got the hose when they were running in the shop. The CO is another story, of course, and now I know all cars need the hose.
 
LC4CARL said:
Here's a Magnaflow I had years ago. Super easy to place.


a-M.jpg



Cat%20003-M.jpg



Cat%20002-M.jpg



PB190013-M.jpg
Click to expand...

Went to a muffler shop and there telling me the only way to fit a cat is with a single unit on the 3" pipe. They suggested to go with a 2.5" inlet model... it would "work" but, I still maintain going with a small 3" inlet cat like yours.

I'll have to go back and show them the magnaflow mini-cats. I don't think I need the heat shield if its that small.



240wagonguy said:
I'm running no cats on my ls swapped C10 and there's no stinky combustion smell.
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That's because it's an LS with it's fancy pants electronics and sensors, individual ignition coil packs, and more accurate "cold wire" MAF.

A 5.0 H.O. is just a classic 302 with mid-80s "hot wire" MAF electronic sequential fuel injection that controls the engine by fuel delivery only.


LS is a Playstation... the 5.0. is an Atari.
 
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