ChevyGuy5

I've been hearing different opinions about getting a high flow cat for a v6. What are the advantages/disadvantages of it?

TomP

There's really no disadvantages...

stock cat (original from when car was new)
-pellet beds break up over time and clog exhaust

high flow cat
-costs less then a new stock cat
-higher flow then original cat
-bolt right in
*might not lower emissions as much as a new GM cat

new GM cat
-very expensive
-higher flow then original cat
-bolt right in
-lower emissions then high-flow cat (tested by Hot Rod on dyno)

new parts store "generic" cat
-more expensive then high-flow, less expensive then GM
-no idea about flow rate
-usually sold as "universals", to bolt in, need to buy $15 kit
-no idea about emissions

GM got "better" at designing cats as they went along... for example, the early cats from the '70's were complete pieces of crap that choked the exhaust flow. That's why people removed them- they instantly felt a power increase.

Later, GM realized that a cat that doesn't choke the engine will produce less emissions- the more efficient an engine is, the less emissions it makes.

So the newer the GM cat the better it flows.

Hot Rod did a test once on a big block using no cat, a high flow cat, and a brand new GM cat. They tested horsepower and emissions. With a new GM cat, the motor only lost 1 or 2 horsepower over an aftermarket cat, BUT, emissions dropped almost 3 times as much! So if you're in a smog-strict state (like California or NJ) you might want to think about dropping the $300+ bux for a new GM cat if you have trouble passing emissions.

Damien00677

keep in mind that GM cat isn't $300 for no reason. There's a lot of engineering in that which is why it flows so well and puts out so few emissions....it could be the platinum internals too

Tom, I assume you have that catco converter that you're always peddling from summit?
You live in NJ too right?
Ever had a problem at the sniffer station

TomP

I don't have catco; it's made by "Products for Power", which was supposedly a Dynomax company. I got it in '96, and it's not in Summit's catalogs anymore; don't know what happened to it... got it for $60. Granted that was 7 years ago... Karl (KED85, where's he been lately?) knows of a source for the PFP cat. I think it's Don's automotive?

I haven't had any problems passing the sniffer with it. In fact, with the old pre-"dyno/ASM 5015" test, the regular tailipipe sniffer during idle, I passed for 2 years with a gutted cat. I didn't know it was gutted until I removed it to put the high-flow cat on.

But I'm sure this ASM 50/15 dyno test would notice- and I've passed that twice, no problems.

camaro_junkie

I just finished putting in Dynomax superconverter #15735 (although the rest of the exhaust is not back together yet, I haven't driven my car for almost two weeks) which I don't think is "high-flow", but it is supposedly better flowing than a generic cat. It looks pretty much the same as the one I took off, but hopefully it's better.

FAST RS

I got a dynomax cat and have never had a problem and i have cali emissions to pass. I pass flawlessy each time my car has 222,XXX miles on the engine.