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Car Forum / Chevrolet / Chevrolet Trucks / August 2008

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Catalytic Convert Replacement

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Mike Dobony - 14 Aug 2008 21:29 GMT
Somebody cut out one of my catalytic converters on my 99 4wd Suburban (also
on my Toyota PU). My concern is that an aftermarket (affordable)
replacement might have a significantly different resistance (backpressure)
than the OEM that they didn't get and cause vibration due to uneven
backpressure.  How significant is this with 2 different catalytic
converters?

Mike D.
Bill - 14 Aug 2008 23:09 GMT
Don't you have a cross over connect pipe on the exhaust?

> Somebody cut out one of my catalytic converters on my 99 4wd Suburban
> (also
[quoted text clipped - 5 lines]
>
> Mike D.
Mike Dobony - 15 Aug 2008 16:20 GMT
> Don't you have a cross over connect pipe on the exhaust?
>
[quoted text clipped - 7 lines]
>>
>> Mike D.

The 2 catalytic converters go into the muffler so the muffler acts as a
crossover.
Shep - 15 Aug 2008 00:43 GMT
Your concerns are scientifically unfounded, just make sure it is an EPA
approved replacement.
> Somebody cut out one of my catalytic converters on my 99 4wd Suburban
> (also
[quoted text clipped - 5 lines]
>
> Mike D.

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Mike Dobony - 15 Aug 2008 16:24 GMT
> Your concerns are scientifically unfounded, just make sure it is an EPA
> approved replacement.

Kindergarten science?  One bank with one measure of resistance and another
with a different measure of resistance causes uneven running.  The
qwuestion is will it be enough to have a significant effect?  Years ago
Bell Aerospace experimented with a partially ducted fan aircraft.  The
vibration tore the engine apart due to unbalanced resistance.

>> Somebody cut out one of my catalytic converters on my 99 4wd Suburban
>> (also
[quoted text clipped - 9 lines]
> http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
> ---= - Total Privacy via Encryption =---
Shep - 15 Aug 2008 21:11 GMT
The difference is like running one cat on a dual exhaust engine and no cat
on the other, the slight difference in back pressure, will not cause a
vibration, if this is what you mean.

>> Your concerns are scientifically unfounded, just make sure it is an EPA
>> approved replacement.
[quoted text clipped - 21 lines]
>> Newsgroups
>> ---= - Total Privacy via Encryption =---

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Mike Dobony - 18 Aug 2008 16:35 GMT
> The difference is like running one cat on a dual exhaust engine and no cat
> on the other, the slight difference in back pressure, will not cause a
> vibration, if this is what you mean.

Yes it will.  One bank with significant resistance followed by another bank
with little resistance will cause vibration.  With no cat there will
definitely be vibration.  With mismatched cats there will be vibration.
That is simple fluid dynamics.  The question is will the difference in
styles and sizes of cats make enough of a vibration to significantly affect
long term engine wear.  Since you reject basic science your answer is
totally invalid.  Go back to science class and study basic fluid dynamics.
Racers understand this and that is why they go to great lengths to balance
flow in intakes and exhaust, especially in those high revving grand prix
racers.
Shep - 18 Aug 2008 21:20 GMT
What vibration are you talking about sound wave pulses, exhaust pulses,
ridiculous. There is no way that doing this will cause something you can
feel in engine vibration ,performance may be slightly, after 45 years of
operating a shop, ASE master tech and former NHRA recorder holder with a 64
Hemi super Stock car, I have experimented and run into all types of issues
like this and never experienced this " "vibration"!  Maybe your terminology
does not describe what you are focusing on?

>> The difference is like running one cat on a dual exhaust engine and no
>> cat
[quoted text clipped - 13 lines]
> flow in intakes and exhaust, especially in those high revving grand prix
> racers.

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Gordie - 22 Aug 2008 04:03 GMT
>> The difference is like running one cat on a dual exhaust engine and no
>> cat on the other, the slight difference in back pressure, will not
[quoted text clipped - 10 lines]
> go to great lengths to balance flow in intakes and exhaust, especially
> in those high revving grand prix racers.

Well now, you have answered your own question haven't you?
Mike Dobony - 22 Aug 2008 14:36 GMT
>>> The difference is like running one cat on a dual exhaust engine and no
>>> cat on the other, the slight difference in back pressure, will not
[quoted text clipped - 12 lines]
>
> Well now, you have answered your own question haven't you?

Nope.  I still do not have an answer about the significance of the
imbalance.  The fact is any imbalance will affect longevity.  The question
is will it cause a significant decrease to the life of the engine.  And now
it is a mote question.  I could not run around with the converter missing.
I had to get one to use the truck.  Good thing I did as the 35 mpg pickup
was stolen.  Now the suburban is both people hauler and construction
vehicle.
 
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