Hi flow catalytic converter

[farmsweet]

Any one running a hi-flow catalytic converters? I'm thinking of putting a pair on my 71 468cu and was wondering if these would quiet the exhaust down. currently I have 3" exhaust pipes off the headers to summit mufflers ,then turned down and out and I know I'm going to have to change them out for quieter ones cause it sounds like a gasser right now.

[PanelDeland]

I'm sure Summit ,PAW or another of the online/mail order places has them.I see no reason to run them on one of these trucks.They aren't required by law and you'll probably get better sound with the right mufflers(meaning ones you like the sound of).There's noperformance or emmisions gain,that I'm aware of.

[skorpioskorpio]

Umm, why would you put a cat on? If you were running a modern LS engine with TPI or something I might understand trying to be environmental about it all but you're running a 468ci, big block I assume, carborated I would guess. I'm not even sure that without the rest of the carb era emissions junk to go along with it that a cat will even last, if it is carburated. I think you should be looking at resonators instead of trying to use a cat as one.

[GASoline71]

A cat won't quiet the exhaust down. With an engine like a 468... it's built to make power. Which is gonna make some noise. Cats are just gonna choke that thing down.

All the popular aftermarket companies make good sounding "quiet" mufflers. Again... when you have an engine like that... you should be prepared for some cab reverb. run the exhaust all the way out the back and use an "H" or "X" pipe... you'll notice a big difference.

Gary

[leftybass209]

A cat is not like a muffler, as it isn't designed to muffle the sound. I would applaud anyone wanting to put a cat on their vehicle, though most people think the idea is obsurd. You really should be looking into different diameter pipes, quieter mufflers, and an h or x pipe if noise is the factor. Exhaust manifolds help also.good luck in your search!
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[Tx Firefighter]

Originally Posted by GASoline71

A cat won't quiet the exhaust down. With an engine like a 468... it's built to make power. Which is gonna make some noise. Cats are just gonna choke that thing down.

All the popular aftermarket companies make good sounding "quiet" mufflers. Again... when you have an engine like that... you should be prepared for some cab reverb. run the exhaust all the way out the back and use an "H" or "X" pipe... you'll notice a big difference.

Gary

The cat will significantly quieten an exhaust. Think back a few years when all the guys with hot rod 5.0L Mustangs used to run an "off road" pipe under them. You could tell from a long way away if a guy had removed the cats or not. Quite profound.

[MARKDTN]

On my '83 K20 wuth TPI I run dual exhaust with Walker high-flow cats and no mufflers. The sound is not that nice. I don't do it for sound reduction, I do it because I have to have them. No way I would have them except they are required.

[Tx Firefighter]

Originally Posted by MARKDTN

On my '83 K20 wuth TPI I run dual exhaust with Walker high-flow cats and no mufflers. The sound is not that nice. I don't do it for sound reduction, I do it because I have to have them. No way I would have them except they are required.

You do have some easy options.

In my case, I have to run a catalytic converter under my dually to pass a visual inspection. There are no functional tests, but it has to be under there when I get my yearly safety inspection. So, a quick Google of "fake catalytic converter" led me to a company in Colorado that sells them in all sizes, and cheap. You're looking at 40 dollars here for a straight through pipe. Mine is 3 inch, but you can choose your size you need from their selection.

I won't go too far into the argument of legality, but it does look like a converter to the eye but it's a smooth straight through pipe inside the case.

[midniteblues]

those hollow converters are cool most guys around here make there own but there never that nice.

I had too put'm on the camaro too get it legal but once it was they were instanly replaced with 3" . I had the system made up with collecters so I could do this easyly and I must say that there definitly was a noticeable sound and flow differnce (I used the magna flow high flow connverters)you could really tell the differnce with revs it would wind up a lil' slower and tend too hover or float in the higher revs just a tad.
after they were off the cat was outa the bag! and it winds up and down with the blip of the peddle.(i'm assumeing this was because of the extra back pressure)the cam didnt sound as lumpy with them on either, the car just flat out loves it without them so do I it sounds sooo much better

[special-K]

I had a '90 Blazer w/350 that had to go through emission. I ran dual exhaust and used two Thrush hi-flow cats. They restrict flow less than a muffler,you can look straight through them. I gave thought to running them on my old trucks,but haven't yet. Why not attempt to help keep the atmosphere cleaner? We do lot of things we "want to" that we don't "have to",like putting shoulder belts in these trucks. I guess I care beyond my own well being. I understand it from an economic stand-point,not spending money you don't have to spend. I've cheated on emissions equipment for economic reasons myself. I had a '99 ZR2 that has three cats. Two "eggs" on the y-pipe and the big one in the single. They were getting all clogged up,truck was running bad,and throwing a code. The "eggs" are not replaceable. You have to buy the whole head-pipe assembly and that was like $700. How much do those tiny things do anyway? One night at my buddy's repair shop we torched them out and reamed the main one out. You don't need to buy anything. It still passed emissions,which is a dyno test taken from the tailpipe. So,there's enough tolerance that cats don't really matter.

[midniteblues]

Originally Posted by special-K

I had a '90 Blazer w/350 that had to go through emission. I ran dual exhaust and used two Thrush hi-flow cats. They restrict flow less than a muffler,you can look straight through them. I gave thought to running them on my old trucks,but haven't yet. Why not attempt to help keep the atmosphere cleaner? We do lot of things we "want to" that we don't "have to",like putting shoulder belts in these trucks. I guess I care beyond my own well being. I understand it from an economic stand-point,not spending money you don't have to spend. I've cheated on emissions equipment for economic reasons myself. I had a '99 ZR2 that has three cats. Two "eggs" on the y-pipe and the big one in the single. They were getting all clogged up,truck was running bad,and throwing a code. The "eggs" are not replaceable. You have to buy the whole head-pipe assembly and that was like $700. How much do those tiny things do anyway? One night at my buddy's repair shop we torched them out and reamed the main one out. You don't need to buy anything. It still passed emissions,which is a dyno test taken from the tailpipe. So,there's enough tolerance that cats don't really matter.

we did this too a 92 blazer and the o2 sensor (even a new one) allways put up a code we thought because it never got hot enough after the hollowing of the cat?

Its funny you said this I've been thinking of hollowing the ones on my
2000 zr2 but I didnt want the same problem we had on the blazer.

after you did it did you notice any improvements? mpg's? seat of the pants?
they dont do the tail pipe up here just a gas cap test and puter check for codes

[Tx Firefighter]

I do understand the moral issue of doing what is right.

I kind of got disheartened when I had my 89 model truck. When I got it, the previous owner was from a non tested county so he removed the air pump stuff from the truck. When I got it, I went ahead and really removed it, meaning I made it appear that the truck never had a smog pump originally. I plugged the manifolds, removed the old brackets and everything. Funny thing is, it still legit passed the of sniffer test by a mile without all of the factory smog stuff (just a TBI 350 with a good cat in the exhaust. I was thinking that I was glad I didn't spend a bunch of time and money to make it all back proper. The emissions stuff is about 50 percent bunk anyway.

On my current 88 dually, it has a TBI 454 and no overdrive and 456 gears. I drive it maybe 1500 miles a year. No more than I would pollute with that little bit of use, I just don't worry about it.

Some government stuff is okay but some is a little too much. I walk a line that lets me sleep at night.
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[c10srule]

run 2.5" pipes with quieter mufflers, wouldnt go any smaller or it will start hurting the performance on that big motor, makes no sense to put cats on the old tuck, like mixing oil with water

[c10srule]

and like said run them all the way out the back, that itself will make a big difference in the cab noise, turn downs are loud inside the truck tried it when i first got my truck going, they werent that way for long

[PanelDeland]

As far as cats.legality and inspections go.Hot Rod(IIRC) did a story a few years ago.It wasn't specific to cats but was about emmisions.They had built a new engine and got it in the car,tuned and running nice.When they took it for emmisions testing it passed with great numbers.When they popped the hood,it failed on visual inspection because some of the emmisions equipment was missing.Then they took it back to the shop,installed the missing emmisions stuff and had to slightly retune to get the car to run right.When they went back for retest,it passed but the numbers were worse.After doing some research,they determined that most vehicles properly tuned would pass the inspections with no emmisions control equipment,but that the emmisions would be lower on the average vehicle John Q. Public failed to maintain properly if it had the equipment.
I didn't intend to hijack,just felt the info might help someone.

[cdowns]

i'd just go with two mufflers on each side the way the factory did with bigblock loluxoboats back in the days of horsepower // i'd think the mufflers are alot cheaper than the cats

[special-K]

Originally Posted by midniteblues

we did this too a 92 blazer and the o2 sensor (even a new one) allways put up a code we thought because it never got hot enough after the hollowing of the cat?

Its funny you said this I've been thinking of hollowing the ones on my
2000 zr2 but I didnt want the same problem we had on the blazer.

after you did it did you notice any improvements? mpg's? seat of the pants?
they dont do the tail pipe up here just a gas cap test and puter check for codes

No issues after that. It sounded a bit throatier and ran maybe a tad better. The vehicles were my wife's rides. I have never personally driven anything that fell under the emissions requirements...either older or diesel. I just keep stuff running right because I take care of whatever I own and like them better that way. I try to avoid mandatory regulations as much as possible and take responsibility as a personal duty.

[farmsweet]

Thanks for the information after some research I found out that 2 1/2" pipes all the way back would do better for my truck as the 3" pipes create a resonance within the exhaust. When the pipes are too big, it alters the resonance and in turn creates turbulence within the piping and messes with the back pressure. Its called Entropy. I still have 3" pipes on my 71 c10 but went with two long quiet mufflers from walker...and no cats..its still loud but sounds way better than before with the small 12" x 4" oval mufflers from Summit.

[AnotherWs6]

2 1/2" is not going to do any better volume wise and with a motor that large you are making good use of the larger 3" system. I have a 396 with 2 1/2" out the back and when I bought it it was AWFUL. Horrible tone, drone, rasp and effing loud. It got old REAL fast. I have 2 chamber flowmasters BTW. I did two things - h-pipe and resonators. The truck is still a BIT loud, but hey , it still has those loud ass flowmasters on there. But the sound quality improved dramatically. No more drone or rasp and I can actually have a conversation if I wanted to.

An h-pipe would be number one on the list to improve the TONE. Mufflers for sound and tone. Resonators for volume. I went with these.....

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

They make em in different lengths and sizes. You can see all of the positive reviews of people who were in the same boat as you and me. You'll see a bunch more similar reviews on Summit's website as well. I bought a Summit H-Pipe kit, two of the resonators and a bunch of Summit brand stainless steel band clamps (great quality, great price too!). Got it all hooked up in my driveway in a couple of hours with no welding. Just a sawzall, tape measure and ratchets. Did it a month or two ago.

You could do the same thing without fabbing a whole out-the-back setup and see what you think and then build off of that if it's still not good enough. It will be unless you're looking for suuuuper quiet.

Bullet mufflers, BTW, = Loud. They are usually jst straight through designs.

[midniteblues]

Originally Posted by special-K

No issues after that. It sounded a bit throatier and ran maybe a tad better. The vehicles were my wife's rides. I have never personally driven anything that fell under the emissions requirements...either older or diesel. I just keep stuff running right because I take care of whatever I own and like them better that way. I try to avoid mandatory regulations as much as possible and take responsibility as a personal duty.

I don't know how I missed this reply.
I still have all oe exhaust on mine but I have a nice ss muffler
For it when I need it. I thought those cans on the y pipe were resonators but I'm not sure.

A friend called me last week and asked if I could weld up his cat. He cut it open and hollowed it out and muffler glued it back together
then when pulling his camper it blew out.
It is a 97 Yukon.
wow did it run and sound better after welding it up.
But now he said it's throwing o2 codes.
I haven't checked it out yet.

We are putting a rough country 2 1/2" lift on the kids 95 s10 blazer real soon an I figure once that is done we are gonna redo the exhaust again but hollowing the cat has me nervous
Because of the o2 sensors throwing codes.

His 92 did afterwards.

Anyway around this?

Here are my 2 magna flow cats for my car.
I figured since I paid for them I might as well save them in case I ever have issues with a inspections(not likely though).
They have the grid type thingy in them.

[davepl]

I'd consider a factory cat like the ones they use on the eRod LS3 engines - I have them on my '69 Camaro. They flow enough for 430 factory net hp, which is more than the 468 likely makes anyway (in factory net trim). My car also has a transverse muffler and between the two idles quiet like grandma's Biscayne. Fast and quiet!

Problem is I don't know how well your fuel trim is controlled. If it gets extra rich, do the converters overheat? I know very little about cats on carb'd engines, although my '75 Monte Carlo had both cats and a carb.

[farmsweet]

Hey Thanks for the suggestion, an H-pipe would be better for the overall flow and tone. Sometimes I think too hard and things just go right over my head. Thanks again for your reply.

[jerry moss]

out here in the peoples republic of california a bunch of you guys would be paying a big fine and/or jail time and your vehicle impounded thats why i drive my old stuff-no smog, no cats, no 02 sensors, no nothing. i work on late model crap every day and some of the stupid ass problems i see make me glad to own older trucks.
as to your loudness problem, run an x pipe, big block flows and full tailpipes and it will sound nice AND still perform like it should. don't waste you time putting cats on it, you will burn them up in no time unless you can moniter your fuel trims correctly.

[special-K]

Originally Posted by midniteblues

I don't know how I missed this reply.
I still have all oe exhaust on....

I don't know why it took four years either!

[wbc409]

Catalytic converters don't work right until they get hot. I was instructed when I was younger not to put cats on a vehicle that wasn't originally equipped because of a lack of heat shielding and the possibility of starting the carpet on fire. I imagine this would be more of a problem with a carbureted engine. Also if the engine runs rich it will ruin a cat fast.