I've read on other boards that there's no such thing as a "high flow cat" for regularly aspirated engines, as they don't push enough air to cause restriction. What's everyone's thoughts on this, as I'm getting ready to do some exhaust mods and would rather stick with the cat I've got if there's no change.

I don't know if there is enough interior area/material to interrupt flow or not. I do know that the input and output sizes are likely to be the same size as your original exhaust, so you're still running big hoses into a small hose for a little bit....

Notes: I've got an aftermarket cat. I *barely* pass emissions with it. I actually had to lean out idle and cruise just to pass.

The old cat may be worth money - more money than a new aftermarket cat...

I am not sure what actual difference there is between the hi-flow and regular ones as far as performance goes, however there is a difference when you look through them. New regular cats when you look through them you can see blurry light/images about the size of a dime at the other end. With my magnaflow hi-flow cat the images were clear and were about the size of a quarter. The other difference is about $50 more for the hi-flow one.

You don't want to open up the exhaust too much w/these engines, unless you are planning to operate above 4k all of the time, you need some amount of back pressure for low end torque.

What I had heard was that the high flow cat thing came up back in the early days of catalytic converters. The early ones were made of a bunch of ceramic beads. Then the newer design was the honeycomb version that flowed better since it had straight through passages. So today most cats are the honeycomb design, so are all high flow versions. I suppose there are some differences in the really high flow cats, like larger passages, larger cross sectional area of the matrix, larger bore inlets/outlets, etc. Probably makes a little difference.

When I was having the exhaust put on my rig a few years back the exhaust guy told me my cat was shot. I told him to put on a high flow and he told me all cats are high flow now days. Then he explained the exact thing you just posted. I asked him how long it would last and he told me not as long as the OEM but you will smash it up anyway so just go with the cheaper one.

Wow i only paid $60 for my magnaflow highflows.. i had some for sale on here and no one even messaged me... 50 bucks more for a highflow? you're getting screwed... i can prob get some more in june....

$60, new generic weld in ones run anywhere from $55-75 at the local parts stores here.

x2. I put a high dollar Random Technology cat on the 4Runner a few years ago. Complete waste of money. My current one is from the parts store on the south end of Moab (Checker?) and works fine for a fourth the price.

Mark

I'm running an inexpensive Magnaflow, tastes great, less filling.