High flow cats?

[Skunksmash]

I need to get a new cat for my '87 Silverado 1/2 ton 5.7L longbed (700R4) and I was just wondering if anyone knew about high flow cats. Are they really high flow? Will you really notice a change in sound or power or anything like that? I mean, they make cats a specific way so that they break up the molecules and what comes out is cleaner, so how could you alter that? Wouldn't changing up the design to flow more result in increased emissions due to less flow on the actual surface area?

[team39763]

The High flow cats should flow better.  I've had them side by side.  The OE cats look thick and restrictive while the HF cats almost looked like a glasspack(you could see though).  On an older truck like yours, I bet it would be a big improvement.  On a newer truck, power and sound difference was minimal since the newer OE cats aren't that bad.  I think the materials inside are different between OE and HF.  I don't know about the efficiency compared to stock cats though.  I'd think they must work or else the Gov't would allow them to sell them as a replacement for a stock cat. 

[Captkaos]

Hi flow cats do flow more, less restriction is a good thing.

[Skunksmash]

Instead of starting a new thread i guess i can just ask my next question in here since it is related. Anyone know what the best stuff is to use to pass the sniffer test? My truck is an 87 so i still have to pass the emissions test for a couple years. There are many products out there that say that if you put them in your tank, you are guaranteed to pass the test. Anyone ever used one or had any experience with one? At this point i am going to school and thus it looks like i can't really afford to buy a cat and have it put on and pay the $40 for inspection. All in all i would be looking at around $210-$220 if were to do that. I found a new cat for $72 shipped, and the cheapest local shop that will put it on is $100. So anyway, i just gave the truck a full tune up so it should have a fighting chance. I just need something for that little extra push over the finish line.

[Irish_Alley]

well there is a lil red bottle looks almost like a shot its that small but its about 8 bucks its the best at autozone but heres the kicker it says guaranteed to pass just like the product "guaranteed to pass" but only if there is no mechanical problems wrong with the truck ex carb cat or anyother problems that cant just be cleaned out like injectors or jets not the products you see don't do anything but clean out the system. they wont clean your cat out nor make you pass if your cats bad, is your cat really bad i mean can you drive they truck, whats it doing.

[Skunksmash]

Well to be honest i am not really sure if the cat is bad. It just looks like it is from 1987, and it probly is. I mean the truck runs smooth as silk but i have had to pass the sniffer test so many times even on newer vehicles that i have built up a little experience with it. On several vehicles (1996 and newer) i have given full tune ups only to have the car fail. Then i would go home and run a can of Berryman's throttle body cleaner through it and just barely pass by the skin of my teeth. And if you have ever used berrymans that way you know that you have to rev the engine a while spraying it into the throttle body (at least thats the way i was taught) and i really didn't want to put my tired old V8 through that, for fear that afterward it might not run smooth as silk anymore lol. As i am sure you know old motors don't really like that to well. I would really rather not push my luck with it, if you know what i mean. So i was looking for another alternative that could help me out.

[Irish_Alley]

well my cat on my 86 passed the sniffer fine i only took it off to put on true duels w/ a high flows that ended up getting punched out and glass packs. if there is nothing wrong with the cat then why risk what like a 100 bucks on a cat and putting it in then it might not even be a problem. IMO just go get it inspected then go from there. one step at a time.

[Skunksmash]

Well somehow, i passed. I really can't explain why i passed with flying colors though. I wonder if it has anything to do with my exhaust splitting into dual right before the back tire? I mean they only use on little rod... weird.