High Flow Cat

[S Pack]

My cat is well on its way out and am thinking of getting a high flow.Already got extractors and 2.5" cat back.Rang up exhaust place and they recommend a 3" high flow if going down this path or just a standard 2.5" for the cheaper option.Just wondering if i will notice and note or performance changes between the stock or high flow.

[SexGod]

hey mate look i just spoke to a guy at my local exaughst place and he reckons unless u have a done up car u wont notice anything at all.

[S Pack]

thanks....i prob will buy as i am slowly doing the car up.this will finish my exhaust system and im getting a bigger throttle body in the next week or two.then im gettin a chip once i save a bit.

[S Pack]

Got 3" high flow cat today car sounds lower drone tone couldnt notice any performance increase at first but there was slightly more power over 3000RPM later during the day.For anyone wondering if its worth getting one -id say get it if your one of those ppl who like doing the whole project but if you want the cheap option or cant be "....ed" dont worry too much about it.

[mattgreen]

i herd it should add alot of power? well thats what people have been telling me? but they also said you should have a decent made exaust system to with extractors and so forth? did it realy not have much of a difference? but yess the tone is nice =] extractors + a highflow cat sounds very nice!

[HoldenManDan]

in my experiences you'll only notice a huge difference if your standard cat it blocked or you've done some big engine mods. Most of the power gain from an exhaust system on the ecotec comes from the extractors, and with that, a headers back system wont give you a HUGE performance gain. If i were you, unless your standard cat is stuffed, save the $$$ and put it towards something else until you actually need a hi-flow cat.

Hope this helps

[dufus]

in my experiences you'll only notice a huge difference if your standard cat it blocked or you've done some big engine mods. Most of the power gain from an exhaust system on the ecotec comes from the extractors, and with that, a headers back system wont give you a HUGE performance gain. If i were you, unless your standard cat is stuffed, save the $$$ and put it towards something else until you actually need a hi-flow cat.

Hope this helps

What he said, like I said in your other thread you will get very little or no gain in sound or performance from a high flow cat.

[Full Spectrum]

I got a high flow cat as it was offered to me at the same price as the stock ****,

Look you might not get 10kw or even 1-2kw.. But what it does offer over the stock **** is free flow, And it's better working with a performance system then stock, You might notice some help between 2800-4000rpm.. But more then likely it wont help take off at all as you need to strangle a system for low down take off torque.

For me the system feels best shooting from 60-90 with 3/4 throttle for overtaking. That mid range.

[immortality]

in my opinion there has to be some gain, like a muffler, it causes a restriction, however little, it is still a restriction. removing it or fitting a higher flowing unit has to give some gain. the gain will only be noticable at higher RPM because at low rpm the flow of even a standard CAT is going to be far greater then actaull exhaust flow through said CAT. this is based on the theory that your only interested in peak power and low to mid throttle driving isn't important. however this isn't the case for 99% of street driven vehicles where it spends more time at idle or just off idle rather then full throttle, then the greater flow of a high flow CAT becomes almost academic because flow restrictions in other parts of the exhaust system designed for street use (i.e. standard OE exhaust as fitted by Holden) is greater then that of the high flow CAT. when fitting a freeflowing exhaust system it is worth fitting a high flow CAT when trying to get that last hp from your exhaust system.

for many years the first thing people did on there brand new commdores here in NZ is pull the CAT's off. yes it was legal and there was a reason they did it, it removed a restriction from the exhaust system

[Not_An_Abba_Fan]

Placebo effect. People thought that it was a restriction, so by removing it, in their mind they increased performance. The difference in back pressure between the front and the rear of a cat is less than 0.5 psi, so unless the cat is blocked, it will have no effect on a stock engine.

Hi flow cats are also worse for the environment on a stock enginge, they need to have a minimum surface area to actually work properly, fitting one with less then the required surface area will not do the job it is meant to do, ie: convert the harmful exhaust gas. They don't get as hot either, so it takes more revs and more load to get them to the "light off" temperature.

[immortality]

when cats were first put on cars they were a restriction, modern cats are a lot better but i'm sure the ones on early commodores were pretty average. just like everything else, designs improve with time.

[immortality]

just out of curiousity, what is the usefull/working lifespan of a catalytic converter? 50,000km/100,000km or maybe 300,000km?

having done a little reading on the subject it's about 7 years or 100,000km assuming it doesn't get damaged or contaminated. contamination thats caused by an engine burning oil or a fouled plug misfiring (and how often do we see theards about oil burning/misfiring commodores?) is enough to contaminate a cat. now assuming that the cat on the average VN/VP - VR/VS commodore isn't blocked i'd imagine there ain't many that are actaully in working condition. but as you say, they can't be a restriction, the placebo effect eh

[Keesh]

vn/vp cats are pretty high flow as it is so its a waste of money.. like immortality said its cause theyre pretty much useless after 200,000 k's anyway.. id agree that its a placebo

[Not_An_Abba_Fan]

By Law, cats had to last a minimum of 40 000kms, until a few years ago, then it went up to 80 000kms. On a properly tuned car you can expect one to last up to 200 000 kms, but as we know, engines do not run perfectly, so they will contaminate over time. If you have one more than 100 000kms old, at least get a temperature test done on it. Quick and easy, and it will tell you if it is lighting off, blocked, or just not working.

[immortality]

i'll put money on the fact that there isn't a VN/VP with original cat that still works unless it's been kept in a sealed chamber or museum and basically hasn't been driven much since the day it was bought. same could be said for 99% of VR/VS commodores, 95% of VT commodores (you find one with less the 100,000km these days) and many VX commodores as well i'd imagine.

as tough as the epa laws are in aussie, unless you have yearly smog tests like they do in california in the US your not going to know how bad it really is.

lets look at this another way, if your going to spend a lot of money upgrading your exhaust, would you fit a factory style reverse flow muffler? i say no. so now that you have spent all that money on improving the entire exhaust system except that poor old original cat that probably doesn't work, and there's a good chance it's also atleast partially blocked....... i think i'd fit a high flow cat (come on now, are you really going to fit a brand new factory unit?). that way i know it's not a flow restriction and it's most likely doing what it was intended to do unlike that crapped out factory fitted cat that died many years ago

[dufus]

95% of VT commodores (you find one with less the 100,000km these days)

Found one
http://forums.justcommodores.com.au/...2-vt-exec.html

[greenfoam]

I've spent alot of time searching the piles of Commodore cats down the wrecking yard unlike Immortality who would be doing well to find a Holden cat in NZ:P lol.

I'd say half of them are broken or completly blown out. BUT allmost all the broken ones have obvious damage to the outsides and have been bottomed out or bashed into something during their life under the car and these are all from cars that were the worst of the worst cars (thats why they are in the wreckers). The other half are in perfect and undamaged condition with no buildup or carbon or anything like that in them.

I've also tested a fully working factory cat against a open cat back to back over the 1/4 and there's less than .1 in it, if anything and that's on a 5 litre let alone a V6 . Alot of bolt on parts are 90% bull**** just so they sell and that's one of them

[vn calais manual]

what is the temperature a commodore cat should be operational at? before and after cat working temps would be good if possible?.

while runing a supercharged v6 with 1'5/8 headers into a 2.5' custom y peice into single standard cat, with a 2.5' single flow system i feel there is a bit more to be had by going to a high flow cat. would this be true? seing that i am runing boost id say the factory cat's wouldnt be up to the task, let alone being that old. guess ill just have to try one out and see how it goes.

[greenfoam]

You might gain something worth while if you're making over 150 rwkw and went to a big cat and a 3 inch or something like that

[slimgrieve]

how do you post a problem on this site

slim grieve

[Keesh]

i no mine probly doesnt work.. my exhaust is way to loud for what it is, and smells like the yarra river on a hot day loll.. probly blown half the crap out the back

[vn calais manual]

You might gain something worth while if you're making over 150 rwkw and went to a big cat and a 3 inch or something like that

it should be well over that once tuned properly. runing a mild cam r/rockers and 10psi cooled. was looking into having a 3' inlet and outlet high flow cat made with another custom y peice, but being 3' this time. will be looking into the full 3' system soog egnough as i can justify one.

[RVN 355]

how do you post a problem on this site

slim grieve

whats the dramas,im a mod

[immortality]

how do you post a problem on this site

slim grieve

go to the top of the main page for VN/VP and click on the "new thread" button, or post in what ever section is relevant to your problem

[Not_An_Abba_Fan]

what is the temperature a commodore cat should be operational at? before and after cat working temps would be good if possible?.

while runing a supercharged v6 with 1'5/8 headers into a 2.5' custom y peice into single standard cat, with a 2.5' single flow system i feel there is a bit more to be had by going to a high flow cat. would this be true? seing that i am runing boost id say the factory cat's wouldnt be up to the task, let alone being that old. guess ill just have to try one out and see how it goes.

A cat should be running at 300+ deg C, but they will light off as low as 250. The rear should be at least 10% hotter than the front.

Having forced induction changes everything. A standard cat will do the job on a factory SC engine, but once you modify it, a metal cat would be better. The ceramic catalyst will melt if it is subject to hi revs and a richer mix for prolonged periods.