Are "Hi-Flow" or "High Performance" Catalytic Converters Really All THAT (and a bag of chips?)?

I guess what I want to know are they worth the money? Just bragging rights? Better than OEM?

My car has the 5.0 Liter TBI. I have installed the Hooker 3" cat back system, the rest of the exhaust is stock. If I replace the cat, will it have to have a 2-1/4 inlet and the 3" outlet? Do they come like that or does a reducer ( or a "bell mouth") have to be welded onto the inlet of the cat?

Any stats to back up performance claims?

Thanx,

shipfitter_sjd

Cut off the reducer on your cat-back and go with a 3" cat. Yes high flow cats are worth it. Stock cats rob power, high flow cats don't. The only way I would use a reducer is if you have headers with a 2.5" y-pipe. Then you will need a reducer to attach the cat to the y-pipe. Then again, I would not even consider a set of headers that don't have a 3" y-pipe. Your stock exhaust is small, crimped and gets an overall grade of terrible.

Or invest in a small hammer and beat the **** out of the stockers and stick them back on. Thats hi-flow

Well he only has one and he would still be plagued with 2.25" piping. Cats are a good thing.

purely opinion. you can argue that the idea behind them is good, and some people hate the sound of an exhaust system without a cat. you can also argue that vehicles don't do any significant damage to the ozone, and that gases naturally emitted from volcanoes do almost all of the damage, which is more cyclic change than actual permanent damage. there is absolute on that topic, only opinion.

IMO, i second the notion to gut it or just remove unless you have emissions testing or a comprehensive visual inspection. if you know how to weld, or know someone who does, you can save yourself a lot of money. but then again, if you get caught running without a cat, you can lose a LOT of money. and gutting it has drawbacks in how the car will sound. i run without a cat on my car, but so do a lot of people in my area.

Pine trees and volcanoes do produce their own polution but are in balance with nature and do not contribute to 99.9% of the particulate emmisions that stick to your lungs from the air you breath every day. Particulates that never leave your lungs as long as you live by simply driving down the road. You may want to take a few more IC engine courses before you make your "opinion" on emissions. It is just something to think about since cats are very cheap nowadays. Especially on cars that are driven everyday. I am sure some of the people who drove in the 60's can can attest to the cleaner air we have today.

EDIT: For track duty I can see going without a cat since the car is only running for a short period every so often. That I will agree on.

I am not a tree hugger nor do I wear Birkenstocks. Lets take care of what we have. America in all respects, is cleaner than it was in the 1960's.

I agree on protecting the atmosphere and the air that we breathe.

I will run the cat. I won't eat green eggs and ham.

Still, all I wanted to know was the answer to my original post.......

How much pressure difference, across the cat converter,
are we talking about?

For a sinlge 3" system with less than 450rwhp, not much. Negligable. Use a search engine to find some test results. There have been numerous tests that show less than a 1hp loss when a high flow 3" cat was added to an existing system supporting 400 rwhp.

a high flow 3" cat can flow almost double the cfm of a stocker. id say the choice is clear. use two of them and expect zero restriction on anything you could drive on the street.

I'd say it's a waste of money on your 305TBI. HOWEVER if you intend on putting in a built 350 or something with alot more hp potential in the future I would say go ahead and replace it with a high flow cat.

i was thinking..

what if you had a cat and you decided to put flanges on each end and then made the same exact size with flanges but with a pipe and had a bolt on bolt off cat you can replace whenever you feel like it in 10 mins while keeping it muffled instead of a cut out

This is a wise idea. You can take the cat out during track time and then bolt it back in when you get home. Plenty of guys go this route. Or you could even put a cut-out in front of the at so that you only have to hit a swith or pull a wire to by pass the cat. Dewey316 is one person that comes to mind that has recently gone this route. You may want to send him a PM so he can send some pics your way.

Regarding the cat or no cat idea - is there an issue with backpressure if the car has no cat? A basically stock TPI car was dsigned with the cat in mind - if it is removed is there a performance loss? You can have too much airflow out the back can't you?

Backpressure is bad any way you look at it. You never want it. People get this confused with scavaging and flow.

Has anyone ever heard of cutting the cat open and removing the internals and welding it back up, or using a pipe to punch through instead of cutting it open, anybody done this...any performance sound gains...

I say "no" to gutting a cat and sticking it back on, might as well stick a straight pipe in it's place - my beater came with a straight pipe. I've heard that the abrupt change in ID of the cat can screw up exhaust flow a lot, then it goes to stock pipe ID and screws it up even more. Might not sound that great, either, in my opinion.

This is commonly done. I agree with pvt num 11. If you gut a cat you should put a stright pipe through it. If not, you will in essence create a hollow chamber that will drastically effect exhaust flow.

My cat was shot when I had replaced my exhaust. Basically all of the internals fell out so they just put it back on empty. I have not liked the sound of my exhaust. It is a flowmaster system that Fbodymotorsports sells. I think is pretty common.

Are you saying that this affects the sound and the performance of the car? Could the sound be a little quieter and not have so much of what I would call a droning (Def. = To make a continuous low dull humming sound) effect? IS there a horsepower issue at hand? Would it be better to put on a highflow cat or go with the straight pipe? Having no cat does produce odors too.

thanks

Cats will tone down the exhaust and make it quieter. It will also eliminate any poping or droning/rasp that you hear. High flow cats do not rob power. Just putting a hollowed cat without a pipe run through it will hurt exhaust flow.

Run a CAT, you never know when your area will start emission testing or you'll move to an area that does like i just did. The new High flow cats work! With new ceramic and extrusion technology they flow way better than the stock cat on your stock third gen that was designed in the early eighties. Some of the new cats have ceramic grids with 2mil wall thickness and way improved flow area vs. the 5+mil thickness of the 80's cats.

Just wanted to chime in on the high flow cat thing. If you have a single cat, a high flow unit is still robbing power. when my motor was stock with just edelbrock headers, a random technology cat, and a flowmaster american thunder system, i picked up 2 tenths in the quarter mile by replacing the cat with a test pipe. single cat systems rob power big time, high flow cat or not.

Absolutely, I don't dispute that at all. Any obstruction in the exhaust stream will make the flow more turbulent and increase back pressure. Newer CAT technology has significantly reduced the back pressure at the same time increasing CAT efficiency. This is being driven by the OEMs who have ever stricter standards to meet. The benefit is if you have to run a CAT, new high flow CATs are way better than the old OEM ones our cars came with and will only help.