High Flow Cat Vs Decat

[Dylaan]

Feel free to flame if this has been made before, but I couldn't really find the answer I'm looking for.

Which would provide better performance and/or sound out of a 3inch 100cell high flow cat or a 2.5inch decat?

I can get my hands on a stock R33 GTS-T cat for free, which I believe is 2.5 inches and turn it into a decat, or I could spend some money on a 3 inch 100cell high flow cat.

Which would you prefer?

Almost forgot to mention I have a 3inch dump/down pipe and 3inch cat back, but a stock cat.

Edited June 9, 2011 by Dylaan

[GTScotT]

The step down to 2.5" for the gutted stocker would hinder it more than a fairly run of the mill 3" cat.

Obviously you realise no cat is going to flow better than A CAT of any type.. Yet there are nonsense legalities and heavy fines for running no cat.. And making it hard to pick (like putting a 3" pipe into the stocker) is a lot of work for reasonably small gains..

It has been covered, but I think this more than covers it for future and ease of searching. Just get a decent cat, save the hassle. Justjap sell decent highflow items for under $200.

GL

[Dylaan]

I know a decat is going to have more flow, but the highflow cat might have an advatage from having the bigger size? How about if I put some mesh inside the decat? would that still count as running no cat at all?

[joeyjoejoejuniorshabadoo]

Buy a 3" straight pipe

Buy 3" cat shell

Cut ends off cat shell

Stick straight pipe in

Weld flanges onto ends

???

Profit

[linkems]

I know a decat is going to have more flow, but the highflow cat might have an advatage from having the bigger size? How about if I put some mesh inside the decat? would that still count as running no cat at all?

LOL

[Dylaan]

Buy a 3" straight pipe

Buy 3" cat shell

Cut ends off cat shell

Stick straight pipe in

Weld flanges onto ends

???

Profit

Could do, but as it is a daily I need it to be at a bit lower volume than a straight pipe. The car is suprisingly quiet at the moment, must be due to having countless mufflers and a stock cat. Could use a few more db before I get in any trouble for it.

Edited June 9, 2011 by Dylaan

[tiels32]

using stock r32 cat i cut off flanges either end and i managed to get a 3" pipe thru it before welding 3" flanges back on. Works a treat

[cannabiscorpse]

I have a highflow cat myself, but i gotta say man- i just saw a decat pipe on the for sale thread for $60 delivered, doesnt get much better value than that.

[-Jimmy-]

My car is too low for them to see the decat to fine me for it anyway.

As said above, I got a nicely made one for a similar price, can't go wrong.

3 advantages for me.

The cat was the lowest point and I was bottoming the f**k out of it. The decat gave me heaps more room.

Bit better flow.

Bit louder and slightly better exhaust note.

Edited June 10, 2011 by -Jimmy-

[karma_syke]

My car is too low for them to see the decat to fine me for it anyway.

As said above, I got a nicely made one for a similar price, can't go wrong.

3 advantages for me.

The cat was the lowest point and I was bottoming the f**k out of it. The decat gave me heaps more room.

Bit better flow.

Bit louder and slightly better exhaust note.

your missing the point, a decat looks like a normal catalytic convererter, they can't tell unless the exhaust is dropped off and they look inside and the honeycombe cores are gone, or you get EPA'd and they check for noxious gases.

[Hanaldo]

your missing the point, a decat looks like a normal catalytic convererter, they can't tell unless the exhaust is dropped off and they look inside and the honeycombe cores are gone, or you get EPA'd and they check for noxious gases.

No that would be a gutted cat. A decat is just a straight piece of pipe with flanges on it. Very easy to tell.

[karma_syke]

i see, in that case couldn't you just run a 'decat' with a catalytic shell? That would be next to impossible to tell.

[cannabiscorpse]

i see, in that case couldn't you just run a 'decat' with a catalytic shell? That would be next to impossible to tell.

That is the dilemma its self. The op is trying to decide whether a decat job (2.5 inch stock cat) is better flowing than a hi flow cat (3 inch)

Also, i know the fines for a decat are suppose to be quite hefty, but couldnt you plead innocence and try to pass it off as being damaged? Unless of course you have the 2.5 inch pipe running through the middle of it, in which case its quite obvious.

[Dylaan]

i see, in that case couldn't you just run a 'decat' with a catalytic shell? That would be next to impossible to tell.

That's what I was planning to do with the stock cat. Probably should have exaplined it better.

That is the dilemma its self. The op is trying to decide whether a decat job (2.5 inch stock cat) is better flowing than a hi flow cat (3 inch)

Also, i know the fines for a decat are suppose to be quite hefty, but couldnt you plead innocence and try to pass it off as being damaged? Unless of course you have the 2.5 inch pipe running through the middle of it, in which case its quite obvious.

Thanks, atleast you understand what I was trying to say

I still don't know what to do, if the cops saw a 3inch dump pipe and 3inch cat back but a stock cat, would they just assume it's been raped of it's inside?

[cannabiscorpse]

That's what I was planning to do with the stock cat. Probably should have exaplined it better.

Thanks, atleast you understand what I was trying to say

I still don't know what to do, if the cops saw a 3inch dump pipe and 3inch cat back but a stock cat, would they just assume it's been raped of it's inside?

Tbh, i think it would come down to the officer. I have had mine sent to the epa (for noise) and the tester didnt even notice the dump pipe (it had factory front pipe though) He did however notice alot of other things lol. In my experience most cops arent too concerned until you have done something stupid in front of them (me, with my foor to the floor) or if you start being a smart arse, then they will without a doubt look for reasons. Their is however exceptions, where they will pull you over and look for anything they can. Most of the time though, the worst they can do is suspect modifications and send you out an epa notice, in which you just swap the parts back over. Also police will look for things like cannon mufflers and front mount coolers, so they can be a magnet for attention.

[Dobz]

your missing the point, a decat looks like a normal catalytic convererter, they can't tell unless the exhaust is dropped off and they look inside and the honeycombe cores are gone, or you get EPA'd and they check for noxious gases.

Not true. A cat that is working stores a lot of heat compared to a gutted cat so all the epa need is an infra-red thermometer to check it's temp compared to the rest of the exhaust.

[karma_syke]

yeah >< i see now, had it in my head that turning it into the cat into a 'decat' was just taking out the honeycomb, not also welding in a straight 2.5/3 inch pipe though it.

[Moodles2]

It's been said by others that driving behind someone with a decat/gutted cat is obvious because your eyes can get watery from those noxious gases

[cannabiscorpse]

yeah >< i see now, had it in my head that turning it into the cat into a 'decat' was just taking out the honeycomb, not also welding in a straight 2.5/3 inch pipe though it.

Plenty of people just bash it out too mate.. Although im under the impression the pipe through the middle is the better option.

[cannabiscorpse]

It's been said by others that driving behind someone with a decat/gutted cat is obvious because your eyes can get watery from those noxious gases

This is why i bought a hiflow- i heard stories like that too. Plus i had heard the fine is huge.