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Shadow_Matrix

Gain of running a decat pipe?

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Hi guys,

 

We are not discussing the legality of a decat pipe here, it is strictly about the power gains. This thread is not for speculation. Has anyone back to back dyno'd or first hand experienced the difference in power between a hi flow cat and a decat pipe.

 

Can anyone also comment on the smell, how bad/strong is it?

 

p.s. I have searched and 100% of the threads are talking about "OMG ULEH, $10K fine!!!"

Edited by Shadow_Matrix

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p.s. I have searched and 100% of the threads are talking about "OMG ULEH, $10K fine!!!"

 

That seems to be a Commodore thing.

 

I run a gutted cat, there's no weird smells, but the back of my car is always covered in black crap. Not sure if it's just running rich though. Not sure if there's much gain to be had by running no cat with something T28 sized. Probably wouldn't even be worth getting a cat with a lower cell count.

 

I think you'll find the biggeer/better gains from exhaust diameter and front/dump design.

Edited by _R_J_K_

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From memory, it's something in the range of a 5kw gain at best. Main reasons for running a decat pipe imo are bleeding-edge gas-flow (great for track cars or streeters making big HP), reliability (no cells to break), cost (decat is free and test pipes are dirt cheap) and testing dyno results (a lot of tuners point fingers at the cat any time there's a problem).

 

To be perfectly honest, I run a quality metal cat not because of fines, but because they make a legitimate contribution to decreasing pollution. My view is that it's irresponsible to run a decat on a street car as anything more than a temporary measure, same way as it's irresponsible to dump your garbage in the bush; the world won't explode if you do, but it's a dick move.

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From memory, it's something in the range of a 5kw gain at best. Main reasons for running a decat pipe imo are bleeding-edge gas-flow (great for track cars or streeters making big HP), reliability (no cells to break), cost (decat is free and test pipes are dirt cheap) and testing dyno results (a lot of tuners point fingers at the cat any time there's a problem).

 

To be perfectly honest, I run a quality metal cat not because of fines, but because they make a legitimate contribution to decreasing pollution. My view is that it's irresponsible to run a decat on a street car as anything more than a temporary measure, same way as it's irresponsible to dump your garbage in the bush; the world won't explode if you do, but it's a dick move.

 

You answered the question perfectly and used a excellent example to describe how much of a shit Kent you are if you run no cat in a pointless situation like 350kw >

 

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From memory, it's something in the range of a 5kw gain at best. Main reasons for running a decat pipe imo are bleeding-edge gas-flow (great for track cars or streeters making big HP), reliability (no cells to break), cost (decat is free and test pipes are dirt cheap) and testing dyno results (a lot of tuners point fingers at the cat any time there's a problem).

 

To be perfectly honest, I run a quality metal cat not because of fines, but because they make a legitimate contribution to decreasing pollution. My view is that it's irresponsible to run a decat on a street car as anything more than a temporary measure, same way as it's irresponsible to dump your garbage in the bush; the world won't explode if you do, but it's a dick move.

 

Ahh Phil. Best poster on NS.com. Always educated answered, typed to precision.

 

Good man.

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From memory, it's something in the range of a 5kw gain at best. Main reasons for running a decat pipe imo are bleeding-edge gas-flow (great for track cars or streeters making big HP), reliability (no cells to break), cost (decat is free and test pipes are dirt cheap) and testing dyno results (a lot of tuners point fingers at the cat any time there's a problem).

 

To be perfectly honest, I run a quality metal cat not because of fines, but because they make a legitimate contribution to decreasing pollution. My view is that it's irresponsible to run a decat on a street car as anything more than a temporary measure, same way as it's irresponsible to dump your garbage in the bush; the world won't explode if you do, but it's a dick move.

Thanks for your detailed answer. What hi flow cat would you recommend around the $400-ish mark? What cat do you run at the moment?

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most 100 cel cats are will do the trick dude. they'll flow well, be good for the environment, AND you'll still bust flames depending on your tune and rest of your exhaust :thumb:

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Thanks for your detailed answer. What hi flow cat would you recommend around the $400-ish mark? What cat do you run at the moment?

 

Is your cat gutted ATM? Otherwise, like said before, that's $400 you could spend on something else that would net you more than 5kw (you will feel no difference). The stock cat does the job fine. And what cat costs $400 anyway?

 

As for the dick move thing, my came like that unfortunately. :/

Edited by _R_J_K_

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Thanks for your detailed answer. What hi flow cat would you recommend around the $400-ish mark? What cat do you run at the moment?

 

Is your cat gutted ATM? Otherwise, like said before, that's $400 you could spend on something else that would net you more than 5kw (you will feel no difference). The stock cat does the job fine. And what cat costs $400 anyway?

 

No I actually run a completely stock s14 exhaust atm. I'm planning to go the CES dump & front + cat (as of now :P ) + fujitsubo RM01A

Edited by Shadow_Matrix

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I just bought a magnaflow 3 inch cat from the US on ebay. part number 94109 and cost about $120 delivered from Chicago and only took a week to get to me. havent put it on yet but im currently running a gutted cat and it f**king stinks at the back of the car. Will see what the fumes are like once its put on.

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I went from a 3inch straight-through (no mufflers) to a cat, mid muffler and rear muffler and made exactly the same power as before. Motor is a 1jz with single turbo.

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I remember reading stock cat vs gutted actually lost 6kw or so back to back due to extra turbulence or something

 

So decat or high flow is best bet

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I went from a 3inch straight-through (no mufflers) to a cat, mid muffler and rear muffler and made exactly the same power as before. Motor is a 1jz with single turbo.

Thanks for your input mate.

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I remember reading stock cat vs gutted actually lost 6kw or so back to back due to extra turbulence or something

 

So decat or high flow is best bet

 

Back pressure hey... Probably on the commodore but not as vital on a turbo vehicle.

 

I ran 3" high flow cast from lukey! No Performance difference but stays legal and responsible

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Also run a Magnaflow MetalCat. Been chugging along nicely for quite some time.

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I just put on my decat pipe (not a hollow cat, proper test pipe)

 

And I was reading that its a defect if you have a cat that's hollow but its a $5k fine if the cat isn't there at all.

 

Now its got me paranoid lol, anyone have any problems with a decat pipe and police?

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I just put on my decat pipe (not a hollow cat, proper test pipe)

 

And I was reading that its a defect if you have a cat that's hollow but its a $5k fine if the cat isn't there at all.

 

Now its got me paranoid lol, anyone have any problems with a decat pipe and police?

 

You won't have problems if you have a cat. Easy as that, don't bother with decats for street cars...

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I just put on my decat pipe (not a hollow cat, proper test pipe)

 

And I was reading that its a defect if you have a cat that's hollow but its a $5k fine if the cat isn't there at all.

 

Now its got me paranoid lol, anyone have any problems with a decat pipe and police?

 

You won't have problems if you have a cat. Easy as that, don't bother with decats for street cars...

 

Yeah thats the thing I have a test pipe lol

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What are u testing? There's no need to not run a cat. That's what everyone's saying, just get one.

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What are u testing? There's no need to not run a cat. That's what everyone's saying, just get one.

 

Test pipe is a name for a pipe that replaces the cat, Im not actually testing anything :lol:

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From memory, it's something in the range of a 5kw gain at best. Main reasons for running a decat pipe imo are bleeding-edge gas-flow (great for track cars or streeters making big HP), reliability (no cells to break), cost (decat is free and test pipes are dirt cheap) and testing dyno results (a lot of tuners point fingers at the cat any time there's a problem).

 

To be perfectly honest, I run a quality metal cat not because of fines, but because they make a legitimate contribution to decreasing pollution. My view is that it's irresponsible to run a decat on a street car as anything more than a temporary measure, same way as it's irresponsible to dump your garbage in the bush; the world won't explode if you do, but it's a dick move.

 

EXCEPT it's made of (super) rare earth metals............... :( Otherwise I agree.

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I had my exhaust repaired at C.E.S here in Brisbane at which point he informed me that my Cat had been gutted (As i bought the car with an existing turbo back exhaust, Damn wogs taking the cheap way out when modifying their car to save on buying a high flow cat).

 

He informed me that on their own dyno there was no real gains to speak of from running a gutted cat (decat) or running a high quality high flow cat.

 

 

And certainly my dyno sheets with my mods aren't any higher than any other similarly modded SR20s on these forums so I'd have to agree with him. However in saying that I do love very much that my car shoots 4 foot flames out the back when I launch it, something that is difficult to do in a car with a CAT.

Edited by Shakey Bones

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This is why cats don't restrict exhaust flow;

 

converter_with_words1.jpg

 

because that honeycomb structure is perfectly straight and the added diameter more than accounts for the reduction of flow area that the metal wafer structure might introduce.

 

Moar honeycombs...

 

structural2008.jpg

 

and there you have it.

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