hi flow cats

Roadster2 · Postby **Roadster2** » Mon Aug 24, 2015 12:34 am

Hey guys I've recently got the headers and catback of my exhaust done but have read about members recommending to replace the old cat with a hi flow cat as they're usually buggered. Given that my car has done 190,000 kms I figured this would be a good idea. Just wondering if there would be a difference to sound (I dont want a raspy noise but I would love a volume increase if possible), and a performance gain. Perhaps a 200 cel cat or a 100 cel cat would help increase the sound ? Any recommended brands, seems like xforce or magnaflow are the general choice. Thanks !

hks_kansei · Postby **hks_kansei** » Mon Aug 24, 2015 1:43 am

THere's a sound increase, but it's only slight,
The note changes a bit more.

Currently I have a 50 or 80-cel cat on mine (cant remember) and OEM everything else, only the tiniest bit louder than stock (seriously you'd not pick it) but it does sound a little dirtier, less smooth.

My old setup had a straight thoughm muffler and the cat made that npticably louder, and a lot rougher sounding, also shot a little flame occationally.

rascal · Postby **rascal** » Mon Aug 24, 2015 3:23 pm

hks_kansei wrote:Currently I have a 50 or 80-cel cat on mine (cant remember) and OEM everything else, only the tiniest bit louder than stock (seriously you'd not pick it) but it does sound a little dirtier, less smooth.

My old setup had a straight thoughm muffler and the cat made that npticably louder, and a lot rougher sounding, also shot a little flame occationally.

Wow that 50/80 cell cat must be pretty hi flow.
My car with no cat used to shoot a flame out the exhaust on overrun (thanks to crappy installer tune) however once I fitted a 200cell cat it arrested the flame, so that only smoke puffed out.

hks_kansei · Postby **hks_kansei** » Mon Aug 24, 2015 5:35 pm

It's only very rarely that it would pop a flame, and would only do it after me having given the car a lot of stick for a decent timeframe (so everything was well and truely hot)

I don't actually know what the cell count is, I bought it secondhand but the guy I got it from said it was a 50 or an 80 (I forget which he said)

I know though that you can see through it pretty easily, each cell was like a macdonalds thickshake straw.

TBH though, I felt no power change once it was fitted, it was all just noise (which really describes my car on the whole)

Roadster2 · Postby **Roadster2** » Tue Aug 25, 2015 1:44 am

Thanks for the info, seems like a 200 cel cat is the way to go..any increase in sound is worth it !

Roadster2 · Postby **Roadster2** » Wed Aug 26, 2015 11:46 pm

any recommended brands without breaking the bank ? I suppose they're all quite similar in performance so I guess i'd be looking at sound. The metal cats seem interesting but out of my range seeing as they go for 200+

project.r.racing · Postby **project.r.racing** » Thu Aug 27, 2015 8:31 am

when i installed my cat, it increased the sound quite a lot. i had a similar system to yours, and did the cat last/separately.

Roadster2 · Postby **Roadster2** » Thu Aug 27, 2015 11:50 am

In what way was it increased? More raspier or a more aggressive note or the same exhaust note but the loudness being emphasised? Also what cat is it that you are running ? Cheers !

project.r.racing wrote:when i installed my cat, it increased the sound quite a lot. i had a similar system to yours, and did the cat last/separately.

speed · Postby **speed** » Thu Aug 27, 2015 6:55 pm

Cats tend not to increase power unless it is the bottleneck in the system, Ie reducing flow.

Currently my cat is a bottleneck but I may not be able to pass the EPA test if I go for a high flow

So it stays for now.

project.r.racing · Postby **project.r.racing** » Thu Aug 27, 2015 9:30 pm

Roadster2 wrote:In what way was it increased? More raspier or a more aggressive note or the same exhaust note but the loudness being emphasised? Also what cat is it that you are running ? Cheers !
project.r.racing wrote:when i installed my cat, it increased the sound quite a lot. i had a similar system to yours, and did the cat last/separately.

raspieness tend to come from a poor designed and flowing big exhaust. ie axles backs etc. exhaust made up of different pipe diameters and flows.

i got same exhaust note, but 20%ish louder.

i forget now what my cat was, thinking 100 or 150 commodore 2.25" version. shop said do this, cheaper option that performance brands but does same job. it worked.

jko · Postby **jko** » Sat Aug 29, 2015 4:24 am

what is the diff between having liek for eg 200 cell or 400 cell? I couldnt find any info on this before buying a new cat, so i just went with a 400 cell one.

I found it weird after installing new genie performance headers + cat that no difference was made in terms of sound? After I drove off out of the exhaust shop, I was quite confused, as I was expecting a louder roar once these were installed.

Black_Penguin · Postby **Black_Penguin** » Sat Aug 29, 2015 9:57 am

Extractors are more likely to change the character of the exhaust note rather than the volume and a hi flow cat would make minimal compared to the rest of the exhaust system.

Roadster2 · Postby **Roadster2** » Tue Sep 29, 2015 12:35 am

I dont think I noticed much of a sound difference after the installation of headers. Perhaps slightly more boomy if at all. I'm still contemplating between a 200cell metal cat vs a ceramic cat, just not sure which one will put out less rasp on my exhaust system.