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Old 6th July 2007, 13:34   #16
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Originally Posted by ananthkamath View Post
I found this through google:

http://www.fluent.us/direct/dieselnet-listing/ex185.pdf

You can see in Fig. 3 that the velocity loss through the cat is negligible, and the contours prove that the velocity in the headers is the same as that in the cat. But the pressure loss is considerable as in Fig. 4. Is this enough to hurt flow and thus power? We dont know yet.
I'm Not Much Into Fluids.. But I feel the equation of continuity says, in a given cross section the velocity of a fuid remains a constant. that is iluustrated in the Pdf as velocity loss being negiglible

Pressure loss is considerable.. Yes. People are trying to overcome that pressure loss only by removing the CAT. Once cat is removed the pressure loss wil become zero across the CAT, giving lesser exhaust flow restrictions, and therby a higher overall velocity.

The velocity through the pie with CAt and without CAT should be considered to find the effect of CAT on flow.

So I feel The pdf justfies removal of CAT
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Old 6th July 2007, 16:38   #17
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Originally Posted by Jomz View Post
I'm Not Much Into Fluids.. But I feel the equation of continuity says, in a given cross section the velocity of a fuid remains a constant. that is iluustrated in the Pdf as velocity loss being negiglible

Pressure loss is considerable.. Yes. People are trying to overcome that pressure loss only by removing the CAT. Once cat is removed the pressure loss wil become zero across the CAT, giving lesser exhaust flow restrictions, and therby a higher overall velocity.

The velocity through the pie with CAt and without CAT should be considered to find the effect of CAT on flow.

So I feel The pdf justfies removal of CAT

No it doesnt. It shows that velocity is maintained through the cat which is good. Surely the pressure loss is what causes the flow decrease, but the question is, is it enough to cause a drastic loss of power on a normal street-driven engine?

PS The equation of continuity doesnt say that for compressible flow. Velocity of flow depends on other factors like gas temperature and animals like sonic effects.
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Old 6th July 2007, 16:56   #18
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Ananth, wouldn't the effect of a cat con vary on the design of it as well. Some designs (ones like shown in the diagram which are connected almost directly to the header) may cause a marginal decrease in pressure, while others (the ones placed further down the line on the undercarriage maybe?) may cause a greater loss of pressure.

Also, pressure is affected by the changes in diameter of the pipe the gas flows through, which in turn causes greater turbulence which may have a negative effect on the scavenging of the exhaust gases.

So in a case where the cat con is connected almost directly to the headers as shown in the diagram in your link, the pressure variance and accompanying turbulence may be less than if the gas has to flow from the headers into the larger collector box and then into the smaller exhaust pipe which then opens up again into the cat con, and once again narrows on exiting the cat con.

All these changes in pressure and turbulence will add up to create a less efficient exhaust. But that brings us to your original question of how much power is actually lost. I got no answer for that.
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Old 6th July 2007, 17:41   #19
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My guess as to the logic of removing the catalytic converter is as follows.

In the figure shown in the pdf file, the catalytic converter is modeled as a porous media, which causes a substantial pressure loss as the gas passes through it. So the pressure at a point B at the inlet of the catalytic converter (i.e., prior to the porous media) will be high, and then drop substantially as the gas passes through the converter and enters a point A at the end of the tail pipe. The pressure at the point A (call this Pa) can be taken as atmospheric pressure. The pressure at point B (call this Pb) will be substantially greater than Pa if the catalytic converter is present.

Let the pressure at some point C inside the engine be Pc. The pressure difference that drives the flow from the engine to the catalytic converter is (Pc-Pb). If the catalytic converter (i.e., the porous media) is removed, Pb will get substantially reduced, i.e., Pb will come closer to Pa; Pc may also reduce, but (Pc-Pb) will increase, thereby increasing the gas flow and the power of the engine. However, as per the carbibles website, some engines may not function correctly if the "back pressure" created by the catalytic converter and the original exhaust manifold/silencer/tail pipe is substantially reduced, i.e., we must ensure that Pc does not drop too much when the free-flow exhaust is added and the catalytic converter is removed. So perhaps that is why one also needs a higher-capacity air filter, and also headers along with the FFE in order to ensure the correct back pressure to the engine.

But I don't support removal of the catcon, because it is dangerous as pointed out by tsk1979, in addition to causing serious pollution.
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Old 6th July 2007, 18:58   #20
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@devilvtec; No, I wasn't intending for India to design an LPG-specific engine. I was suggesting that if automotive manufacturers can spend billions for developing engines for unproven or specific fuels as bio-diesel, why not give LPG a shot, which is far cleaner than petrol itself, has higher MON, and better combustion characteristics.


@rks;

By given assumptions;

Pa= Pressure of exhaust gases at exit (tailpipe-taken as atm.).
Pb= Pressure of exhaust gases at entry of cat-con.
Pc= Pressure of exhaust gases at exhaust manifold/runner.

Pressure difference between cat-con entry & manifold= (Pc-Pb)=X1; since Pc is always greater than Pb.

Pressure difference between cat-con entry & tailpipe= (Pb-Pa)=X2; since Pb is always greater than Pa

Now, with cat-con, the value of X2 is always higher than X1. The objective is to reduce the restrictiveness of exhaust flow such that X1 equals X2, as far as possible, without actually reducing pressure at the runners, correct?

Easier said than done. Having cat-cons at the manifold end might reduce X1 by a large percentage, but incorporating them, especially for turbo/high-performance applications, is a headache.

For certain cars like the Tiburon, where minor mods to the intake/exhaust can liberate quite a few horses, removal of cat-cons are stage 1 of aftermarket mods.

Again, like mentioned earlier, cat-con removal is not required unless gunning for serious numbers....
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Old 6th July 2007, 19:29   #21
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Like Robin has mentioned some cars come with cat cons at the centre of the car right under the rear passengers footwell.

I am bad at chemistry, but what about the smoke emitted by diesels? Are they as harmful too. Because I see most diesels (including the CRD's) smoke out to glory when petrol cars hardly emit smoke (I am talking about modded).

Anant, I am not quite sure. But, the baleno has a small muffler after the headers, then the catcon before the exhaust gases are emitted out of the restricted end can. On removing them I did find a change in drivebility. I was running a centre muffler for speedrun and on reaching bangalore added another muffler to muffle the noise. And once again there is some change with the way the car moves. Though i cannot quantify how much of a difference it is.

Last edited by mclaren1885 : 6th July 2007 at 19:31.
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Old 6th July 2007, 20:31   #22
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As far i can understand, that cat acts looks like an expansion chamber! and more over, by reading what you guys have posted here, all i can understand is that the gas expands in the cat, which serves the same purpose of an expansion chamber! and expansion chambers are supposed to increase performance rit?
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Old 6th July 2007, 20:41   #23
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Well a easy example of cat restricts power is the Baleno.

The Bharat Stage II Baleno produces - 94bhp
The Bharat Stage III Baleno produces - 91bhp

Thats loss of 3 bhp from Bharat Stage II to Bharat Stage III, so does the Bharat Stage III Baleno have a more restrictive cat?
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Old 6th July 2007, 20:47   #24
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Originally Posted by BUSA View Post
Thats loss of 3 bhp from Bharat Stage II to Bharat Stage III, so does the Bharat Stage III Baleno have a more restrictive cat?
The exhaust apart from being restrictive another reason Maruti quotes for the drop in power is the addition of EGR. Which again is exhaust related.
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Old 7th July 2007, 00:28   #25
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As far as I know, in most cars the cat con is placed right after the headers. This is done to "light off" the catalyst, i.e. to increase its temperature as soon as possible to get it working efficiently.

The baleno is one exception for some reason. Any other car you guys know of?

It definitely matters where the catalyst is placed, but more important is the flow capacity of the cat itself. Dyno testing seems to be the only answer. Can anybody point to a source with this kind of information?
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Old 7th July 2007, 00:32   #26
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Quote:
Originally Posted by veyron1 View Post
Most ECM's won't detect the cat-con; lambda sensor's at the exhaust manifold, na...there aren't separate sensors for cat-cons in most cars...at least not the non-expensive ones...
Take a look at late model cars, you'll find another o2 sensor after the cat.
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Old 8th July 2007, 12:21   #27
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ok guys so is there any FFE maker out there (maybe automech) who will be ready to incorporate the catcon in an FFE for my existing santro xing erlx. I currently use a catback exhaust so I guess I am not polluting. I am sure if I have an FFE w catcon I wont get the best drag race performance but then I just need a decent improvement low/mid end torque and am ok with not getting the max out of the FFE, if I don't pollute

slightly OT - was just watching the "Live Earth Live" concert on VH1 and its created a lot of awareness in me, switched off all the unused gadgets in sleep mode drawing power Its we started contributing to saving our planet now
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Old 14th August 2007, 10:29   #28
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Guys I wanted to know whether getting rid of the Cat-Con on the Palio will make any different to the performance? I plan to do my FFE in installments (part by part). First getting rid of the cat and replacing it with a straight pipe. Then removing the exhaust manifold and this straight pipe with a 4x2x1 header made in SS. Then get rid of the auxillary muffler and adding an expansion chamber in place. And last will upgrade the end can to a free flow. Does this idea sound stupid? If yes, why?
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Old 14th August 2007, 11:21   #29
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moral I am pretty sure you have seen the manifold of the 1.6 as it was there in the forum in one of the threads. What I remember is that there is literally no distance between the manifold and cat (this might be different in a post NV 1.6 ). So its going to be difficult to get the cat off and replace it with a straight pipe. I guess if you are going step by step then combine cat removal ( though I wont recommend it... I love mother nature) and custom headers.

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Originally Posted by moralfibre View Post
Guys I wanted to know whether getting rid of the Cat-Con on the Palio will make any different to the performance? I plan to do my FFE in installments (part by part). First getting rid of the cat and replacing it with a straight pipe. Then removing the exhaust manifold and this straight pipe with a 4x2x1 header made in SS. Then get rid of the auxillary muffler and adding an expansion chamber in place. And last will upgrade the end can to a free flow. Does this idea sound stupid? If yes, why?
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Old 14th August 2007, 11:51   #30
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Originally Posted by rishibravo View Post
as it was there in the forum in one of the threads. What I remember is that there is literally no distance between the manifold and cat (this might be different in a post NV 1.6 ).
No there are no differences in the cat-con placements for the Pre-NV as well as the post-NV models.

This is a Pre-NV manifold removed - http://www.team-bhp.com/forum/516433-post51.html

This is a manifold as found on the engines of the 1.6 Stile -
http://www.team-bhp.com/forum/497739-post22.html

Quote:
So its going to be difficult to get the cat off and replace it with a straight pipe. I guess if you are going step by step then combine cat removal and custom headers.
Its not difficult Rishi, if the garage you get work done at is equipped with a ramp to get underneath the car. There are five bolts each on two plates to hold the cat together.
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