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Discussion Starter #1
When I was in my teens we used to knock out the guts of the cat converters so it was there but not restricted can that still be done with out messing up the computer? Yes I know its illegal but im not robbing a bank or anything whats your thoughts on it? :)
 

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Cars are now designed to operate WITH a functioning catalytic converter. Although I have not seen the results of hollowing one out, I would think it safest to leave it alone or just get a higher flow cat. Personally...if my car comes with one, I keep one attached and functioning.

RN
 

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It has to be there.

The downstream O2 sensor must compare with the upstream and show a decrease in NOx.

I've been in this business for many years. What happens most of the time is that the hollowed out cat creates a random exhaust flow because the open interior messes with the designed exhaust scavenging.
Most will actually lose useable power and notice that the torque band has shifted to a higher rpm.

This is from first hand experience. In my yourger days, I've been guilty of cutting without thinking.


As a side note, most high flow cats are only about 5% greater cfm flow. Hardly worth a few hundred bucks.
This higher flow may unleash a few ponies, but only at the highest rpm range. Not too many daily drivers keep the rpm at 5700 all day.
 

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MX-5 said:
It has to be there.

The downstream O2 sensor must compare with the upstream and show a decrease in NOx.

I've been in this business for many years. What happens most of the time is that the hollowed out cat creates a random exhaust flow because the open interior messes with the designed exhaust scavenging.
Most will actually lose useable power and notice that the torque band has shifted to a higher rpm.

This is from first hand experience. In my yourger days, I've been guilty of cutting without thinking.


As a side note, most high flow cats are only about 5% greater cfm flow. Hardly worth a few hundred bucks.
This higher flow may unleash a few ponies, but only at the highest rpm range. Not too many daily drivers keep the rpm at 5700 all day.
So the best thing to do is keep the cat as long as it works and if need be, get a freer flowing exhaust (leaving cat alone)?

RN
 

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The muffler is the single restriction in the PT exhaust.

You must also realize that changing the backpressure changes fuel economy, and not always for the better.
An open exhaust will scavenge the cylinders so fast that you won't get a complete burn.
Less backpressure also moves the torque band upwards in the rpm range.

That said, I have a less restrictive muffler. I'm not on an OEM exhaust soapbox.
I'm just pointing out some of the consequences of changing a well engineered system.
 

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MX-5 said:
The muffler is the single restriction in the PT exhaust.

You must also realize that changing the backpressure changes fuel economy, and not always for the better.
An open exhaust will scavenge the cylinders so fast that you won't get a complete burn.
Less backpressure also moves the torque band upwards in the rpm range.

That said, I have a less restrictive muffler. I'm not on an OEM exhaust soapbox.
I'm just pointing out some of the consequences of changing a well engineered system.
Thanks for the info.

RN
 

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Also, if they perform an emissions test for vehicle inspection (like they do in this area of PA) and you've removed the guts from the catalytic converter, your car will be failed on emissions.
 

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MX-5 said:
The muffler is the single restriction in the PT exhaust.

You must also realize that changing the backpressure changes fuel economy, and not always for the better.
An open exhaust will scavenge the cylinders so fast that you won't get a complete burn.
Less backpressure also moves the torque band upwards in the rpm range.

That said, I have a less restrictive muffler. I'm not on an OEM exhaust soapbox.
I'm just pointing out some of the consequences of changing a well engineered system.
I've read the same opinion from several knowlegable sources & dyno results.
That's why I decided to just change to a Dynomax Muffler & leave the rest of the exhaust system alone &. save the money for other Mods.
 

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, hee that last one was me,,
,,
mx is right , the comp will set off codes, every so often as it will not see any diffrence between the 2 sensors, they are about, 1 and a 1/2 feet appart,
,, if you do hollow it out,, ,
you will see much improvment if you have an aftermarkt turbo , which will spool up much faster,
but im not sure waht it will do on the pt-turbo 2003s,
theres so many codes going in that computer, im sure you would set of a engien light right away,
,,
with a stock pt ( 2001-2002) ,with an aftermarket turbo, you will pop a code,
if the mixture is to rich, or too lean, , and with no computer controler, it will happen often, ( ie riseng rate fuel press reg)
, , the way to do it is to not compltetely howoll it out, but prehapse a 1 and a 1/2 inch hole all the way threw,
or most of the way,
, the converter is , in i think 4 sections,
each about 1 and a 1/2 inches thick,
with a noticable space inbetween each layer.
, or maybe,
take the top layer out, and the bottom layer out,
though the bottom, is harder to get to as the pipe is curved on the bottom,
,,
alos the pipe is , a pain to break from the the rest of the exhaust, not sure what chrysler was thinking when they made that clamp,,

,
i have first hand ex[perince also with this,,
, i would just recomend getting a high flow cat,, and hope it doesnt pop codes, to often if at all,
,
good luck,
 

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MX-5 said:
The muffler is the single restriction in the PT exhaust.

You must also realize that changing the backpressure changes fuel economy, and not always for the better.
An open exhaust will scavenge the cylinders so fast that you won't get a complete burn.
Less backpressure also moves the torque band upwards in the rpm range.

That said, I have a less restrictive muffler. I'm not on an OEM exhaust soapbox.
I'm just pointing out some of the consequences of changing a well engineered system.
I agree with most of what you said here. That is why I just replaced my muffler. I chose the suppertrapp because it weighs only about 5lbs. and is tuneable buy adding and removing plates. It has worked great.

I have a problem with what you said about open exhaust, It doen't scavenge. It just allows the exhuast to just dump out. You need that impulse to travel out and down the exhaust and return back by bouncing of something and returning back to the closed exhaust valve. Then bouncing back down the pipe creating a vacume so when the exhaust valve reopens it sucks out the exhaust.
Over scavenging usualy only ocurs with race type cams with big overlaps ( intake & exhuast open at the same time). The Ideal is when you have a good enough scavenging, to not only pull the exhaust out during the overlap, but pull the fuel and air mix in as well. Over scavenging can pull the intake mix right on through wasting fuel or sometimes contaminating it intake charge with exhaust gasses. That is one reason why people often get dissapointing performance but putting in a larger cam than they need. :)
 

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image guy said:
I have a problem with what you said about open exhaust, It doen't scavenge. It just allows the exhuast to just dump out.

We'll have to agree to disagree.
;)


I've had a lot of experience fixing this simple mistake made by many. While changing nothing in the motor, just removing the exhaust in favor of straight pipes, the useable torque and fuel economy suffers.

This is more pronounced with the smaller 4-cylinders in the import race group. A 2-valve per cylinder big block V-8 is so inefficient that the degradation is less noticeable.
 

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MX-5 said:



We'll have to agree to disagree.
;)


I've had a lot of experience fixing this simple mistake made by many. While changing nothing in the motor, just removing the exhaust in favor of straight pipes, the useable torque and fuel economy suffers.

This is more pronounced with the smaller 4-cylinders in the import race group. A 2-valve per cylinder big block V-8 is so inefficient that the degradation is less noticeable.
What are we dissagreeing about? As far as I can tell we both are saying open exhaust is not helpfull. I just dissagreed with your use of the term scavaging.
Maybe you can explain what it means to you? Or maybe re-read my post before jumping off :)
?:|
 

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image guy said:


What are we dissagreeing about? As far as I can tell we both are saying open exhaust is not helpfull. I just dissagreed with your use of the term scavaging.
Maybe you can explain what it means to you? Or maybe re-read my post before jumping off :)
?:|


An open pipe system can have very positive scavenging effects in the cylinder, if the tuned length is correct, often better than a 'free-flowing' muffler.
The impulse (reflection or shockwave) that is generated and reflected back into the combustion chamber is caused wherever there is a abrupt change in pressure (This most oftne occurs where pipe diameter changes, significant thermal differneces, or increased resistance due to fouling). The inlet to a muffler chamber, or the exit from an open pipe both offer a significant delta in pressure, and will cause the desired 'reflection'. The significance of this however, is truly based on the tuned length of the system, and the effective valve timing of the exhaust. You do NOT need aggressive cams or timing to take advantage of proper exhaust system design.
There are many freeware Java calcualators to help you design and tune your custom exhaust system, just be prepared with all the application specifics for your vehicle.....

Brad
 

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Powertrip said:




An open pipe system can have very positive scavenging effects in the cylinder, if the tuned length is correct, often better than a 'free-flowing' muffler.
The impulse (reflection or shockwave) that is generated and reflected back into the combustion chamber is caused wherever there is a abrupt change in pressure (This most oftne occurs where pipe diameter changes, significant thermal differneces, or increased resistance due to fouling). The inlet to a muffler chamber, or the exit from an open pipe both offer a significant delta in pressure, and will cause the desired 'reflection'. The significance of this however, is truly based on the tuned length of the system, and the effective valve timing of the exhaust. You do NOT need aggressive cams or timing to take advantage of proper exhaust system design.
There are many freeware Java calcualators to help you design and tune your custom exhaust system, just be prepared with all the application specifics for your vehicle.....

Brad
:) That is how I understand scavanging. I maybe over generalized . I was mainly refering to guys that just disconect their exhast at the track or put on a huge pipe thinking it will help. But Yes I agree with you completely. That is one of the reasons the old "stepped " headers worked so well :)
 

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image guy said:
That is one of the reasons the old "stepped " headers worked so well :)
Well I have to disagree with the stepped-header thing. I have *never* seen any proof that any stepped configuration adds any effective power. I have actually asked certain manufacturers to provide actual 'results' to prove their claims, but none have ever materialized. Unfortuantley, the gains from the modest size stepping in the headers woudl be at such a high RPM band, that I don't think that realistically any gain is possible. THEORETICALLY on the other hand, is is possible.
But that of course, is must my opinion :)

Brad

http://www.headersbyed.com/stepped.htm
 

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Discussion Starter #18
thanks I will be leaving the cat alone I dont want problems just fun :)
 

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II think
Powertrip said:


Well I have to disagree with the stepped-header thing. I have *never* seen any proof that any stepped configuration adds any effective power. I have actually asked certain manufacturers to provide actual 'results' to prove their claims, but none have ever materialized. Unfortuantley, the gains from the modest size stepping in the headers woudl be at such a high RPM band, that I don't think that realistically any gain is possible. THEORETICALLY on the other hand, is is possible.
But that of course, is must my opinion :)

Brad

http://www.headersbyed.com/stepped.htm
x( iI am startinng to think some of you guys just need to be right .
Of course it might only help at high rpm you always need to design intake cam , head flow ,comp. ratio to work in rpm range needed you need to consider vehical wieght gear ratio. You need to consider the whole pkg. But this argument is BS . Seems to me any way :\
 
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