Cat Removal Really Helpful?!

[jasoncitrano]

Ok I'm one of the guys who will do anything for a few extra ponies, so when i got my 3'' turbo back exhaust I left the cat off.

So after the new exhaust is on, I personally noticed big performance gains, and lower spool up times. So I bring my car into workshop for school, I go to Universal Technical Institute http://www.uticorp.com/default.aspx?tabid=28&bhcp=1
My teacher INSISTS that I should not have removed my cat as i will lose performance gains. He claims that when the cat is heated to operating temperature it literally pulls the exhaust from the engine and when you hack it, it slows the exhaust flow down.
What's your input on this topic guys??

P.S. i'm awd so no need to worry about emissions.

 

[AWD90DSM]

well i could be wrong, but heres my take on it... on an N/A car, the cat provides some backpressure, which helps your motor produce torque. but on a trbo car, the turbo itself is providing packpressure. and in a turbo application, the most efficient exhaust is no exhaust at all, so really you want the straightest, least restrictive exhaust path for the turbo to spool and hold boost without added resistance.
just my .02

 

[turbolover2]

There are a lot of theories on this. But, in my experience, no cat is always better, on any car I've tried it on.

 

[Defiant]

My teacher INSISTS that I should not have removed my cat as i will lose performance gains. He claims that when the cat is heated to operating temperature it literally pulls the exhaust from the engine

I'd like any kind of backup for that fairy tale. And he's a teacher, eh?

Welp, there ya go.

 

[IHeartTurbo]

I'd like any kind of backup for that fairy tale. And he's a teacher, eh?

Welp, there ya go.

Don't post about what you don't know anything about. Just so you know, the teachers here at UTI are all people who have been working in the field for a long time. And every one of them that I have had has been very knowledgeable, almost to the unnecessary point. I'm not saying he's right, and I'm not saying he's wrong, but you don't know any of them and shouldn't be making judgements.

By the way, who said that about the cat? Just wondering.

 

[jbranne]

I'd like any kind of backup for that fairy tale. And he's a teacher, eh?

Welp, there ya go.

Werd.

The cat is just a restriction, plain and simple. I won't get into the whole backpressure debate, but backpressure is ALWAYS a bad thing, but people confuse that with scavenging. It doesn't matter too much for the turbo guys since they can't use scavenging to their advantage much anyway.

In any case, I'll say this. I would recommend installing a high flow aftermarket cat. The cat reduces emissions DRASTICALLY, and even if you don't have to get tested, it's just irresponsible to hack it. That the REASON many places now test for emissions....because people modify or don't maintain their cars.

Also, the tree huggers like to use this kinda stuff as ammo. It's up to all of us as car guys not to give these guys an inch. if they had their way, we'd all be driving Metros or hybrids. None of us wants that, so the best thing we can do is keep our rides as clean as possible.

Using a high flow cat won't cost you much HP, but it will go a long way for emissions and the image of those of us who mod cars.

 

[XxSiRhCy6PxX]

i know removing the cat will make your car louder but will it make the sound deeper as well? im planning on removing my cat too but i dont want my car sound like crap

 

[4geze63]

i went from a highflow 2.5" cat to a test-pipe, much better

 

[jasoncitrano]

Well, I'm in the Driveablilty course, phase 4. My teacher is Mr. Allen, IHEARTturbo, and you know he knows his shit. He's 1 of 4 people in IL that goes around to dealerships and fixes the problems that thier lead techs can't. He has over 10 years racing experience. He stated that "yeah a turbo provides suffiecent back pressure only up to the point while it's in vacume. Once its out of vacume it's sort of just pushing the exhaust along. I have my cat off and i will say i DID notice a difference but i was just curious on why he was so against removing it. He has been racing twin turbo mustangs he says and has left the cats on all of them. He did also explain scavenging but I was always told a turbo provides enough pressure???

 

[jbranne]

Scavenging and backpressure are two totally different things, and from what I can tell, very few people know what'as really going on there. I typed up a big explanation for another board....I'll start another thread and cut and paste it.

 

[Defiant]

Don't post about what you don't know anything about. Just so you know, the teachers here at UTI are all people who have been working in the field for a long time. And every one of them that I have had has been very knowledgeable, almost to the unnecessary point. I'm not saying he's right, and I'm not saying he's wrong, but you don't know any of them and shouldn't be making judgements.

I'm replying to what you say he said: "He claims that when the cat is heated to operating temperature it literally pulls the exhaust from the engine and when you hack it, it slows the exhaust flow down." Did you misunderstand him, or does he have some kind of knowledge about mystery mist magnetics that not even Tesla had suspected? I want backup for this idea of a cataclysmic diverter which at "operating temperature it literally pulls the exhaust from the engine". Either you heard wrong, there's something more to chimneys than I've run across, or there's a problem with the interface between reality and fantasy.

 

[jasoncitrano]

No, I didn't hear him wrong. I even asked him about it twice. I wrote exactly what he said to me. I've been trying to figure what he means by this. But basically what I think he was getting at is that the back pressure that is created from the converter creates scavenging and therfore does not burn the exhaust valves. The only reason this became an issue is becuase we lifted my car up on the lifts and he saw it and said i'm losing performance becuase i thought "it was cool to cut the cat off." I told him over and over that I literally felt a difference in spool up and everthing but he insisted that when the cat is fully heated the hot material on the inside, either beads or honeycomb help to pull the exhaust out rather then have to have the engine pump them out. I don't agree with him at all, but he is a very hard person to argue with.

 

[terminaltsi]

i really dont know why he would say that. i went to uti also, and found that most teachers were very knowledgeable to a point, but when it came to modern turbo technology, they didn't know as much as they should have. 99% of street turbo dsms will make more power with no cat. hell, we've all felt the difference when we get rid of the stupid thing.
HOWEVER: thats comparing a stock cat to no cat. a modern new high flow cat will probably not make nearly as much difference in hp. i remember somewhere a dyno found maybe a 1-2 hp loss with a high flow cat.

but....ask your teacher to dyno your car with no cat and with your stock cat in place and end the argument.

 

[jasoncitrano]

i would but all we have here is a fwd or rwd dyno boo!!!

 

[Defiant]

No, I didn't hear him wrong. I even asked him about it twice. I wrote exactly what he said to me. I've been trying to figure what he means by this. But basically what I think he was getting at is that the back pressure that is created from the converter creates scavenging and therfore does not burn the exhaust valves.

Oh, dear. Now it's the exhaust valve stories. I like the one about them warping when cold air hits them. All these decades, and I'm waiting to see the first one.
I've not heard of what he's talking about. Which sure doesn't mean I can't be wrong.

The only reason this became an issue is becuase we lifted my car up on the lifts and he saw it and said i'm losing performance becuase i thought "it was cool to cut the cat off." I told him over and over that I literally felt a difference in spool up and everthing but he insisted that when the cat is fully heated the hot material on the inside, either beads or honeycomb help to pull the exhaust out rather then have to have the engine pump them out. I don't agree with him at all, but he is a very hard person to argue with.

I'd show him hard.

 

[IHeartTurbo]

Yeah Mr. Allen definitley knows a lot. He's definitley one of those people that it's scary how much he knows. But I definiltey disagree with him on this. I'll talk to him next time I see him and see what I can get outta him.

Oh and doesn't 4 suck? 5 is even worse just so you know.

 

[jasoncitrano]

Yeah 4 does suck! and thanks for the heads up! Like Iheartturbo said the teacher who said this was very knowledgeable but again I personally have never seen the burnt valves either but that doesn't meant it can't happen. I need an arguement to aproach him with so I have some backup for why running no cat on racing applications is better!!

 

[tsi_daggie]

the only reason that running no cat or a hollowed out cat can hurt your valves is becuase the cat helps with back pressure and holds heat back and with no cat when you shut the car off it allows the valves to cool faster.

that is what an exhaust shop told me.

but i have run cars with no cat or a hollowed out one and all i noticed was the raw exhaust smell and worse gas milege.

just my .02

 

[AirProE]

Seriously, I would like to see some more back up information (hard theoretical would be nice) as to how a warmed up cat (basically a big catalyst that looks like a filter to me) can literally "suck" air through the exhaust. Why is it that pretty much everywhere I read, turbo race cars have no cat unless rules specify they have to have one? Very interesting, I can see the whole bent valve thing (in theory, but other than making the valves brittle, not sure about the whole bending thing). Either way, seen a whole bunch of cars run catless without issue (Mustangs and Camaros come to mind). If he could show you a mass flow equation that takes into account the cat DeltaP, using the turbo back as the closed system, then post it. I'm interested in seeing it.

--AirProE

 

[Nanan]

Your teacher might be smart when it comes to non turbo engines but he needs to learn a few things when it comes to turbo cars and exhaust flow.

On turbo cars they almost always have posative pressure in their exhaust manifold, on our cars this can range from 10 to 60 Psig. Even when running under vacuum the exhaust pressure is still posative due to the turbo causing restriction. Even with the largest monster turbo and a free flowing 3" exhaust system in use it will still have manifold pressure.

I know this not from reading but from actual testing, I am going on 8 years of working experiance with turbo mustangs, dodge GLH cars, and DSM cars. My friends and I have tested the backpressure theory, the valve warp theory, and the scavenging theory, none of these apply to turbo cars.

Tell your teacher to hook up logging pressure gauge to turbo exhaust manifold and test it for himself if he doesnt believe it.

If you donot have to run a cat then feel free to remove it but its not exactly eco friendly, if you can go to a high flow cat then it would be the wiser thing to do.

 

[snoozin]

more info on backpressure than you can shake a stick at.

http://www.dsmtuners.com/forums/showthread.php?t=168578

 

[jasoncitrano]

Well, i have the cat off already i'm totally for ripping those damn things off. I am in now way shape or form agreeing with my teacher at all. He has many years racing turbo mustangs as well. Which I still don't understand why he would say this...??? Just out of curiosity I want to see who all has their cat actually removed. I'm never putting mine back on, infact it was so rusted I don't think it's even usable anymore. All this info is great guy keep it coming. Just adding to the firepower i can use to argue with my teacher!!