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Hollowing out an LT5 cat on stock manifold. Anyone do it?

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Hollowing out an LT5 cat on stock manifold. Anyone do it?

Old 08-09-2018, 10:27 PM
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billschroeder5842
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Default Hollowing out an LT5 cat on stock manifold. Anyone do it?

Has anyone ever "hollowed out" the cats on their stock LT5 exhaust manifold?

I'm doing my usual angst about exhaust upgrades on my 91 ZR1. I wondering how hollowing out the cats make a difference and if anyone had any experience with it.

I'm just curious....

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Old 08-09-2018, 11:41 PM
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JerriVette
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Fwiw todays caralytic convertors are so efficent it doesnt pay to hollow them out...

there is really no benefit to doing so

hth
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Old 08-10-2018, 02:57 AM
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Just bit the bullet and do headers/exhaust. 91 exhaust system is not the best flowing to start with.
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Old 08-10-2018, 06:51 AM
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Originally Posted by FASTAZU View Post
Just bit the bullet and do headers/exhaust. 91 exhaust system is not the best flowing to start with.
I agree

the factory headers on the early cars are tough to modify and the big can cats are tough as nails and it's better to install the headers as suggested. cats really only cost around 5 hp and due to the turbulence of a big empty can they would likely not gain much due to very poor scavenging of the engine. no bueno, sell them and use the money to do the right thing.

the stainless works headers can be had cheaper now and the obx are around 500 and seem to be OK (like to hear more).

the exhaust needs all the help it can get to let the beast breathe

Last edited by Rkreigh; 08-10-2018 at 06:53 AM.
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Old 08-10-2018, 08:34 AM
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Originally Posted by Rkreigh View Post
I agree

the factory headers on the early cars are tough to modify and the big can cats are tough as nails and it's better to install the headers as suggested. cats really only cost around 5 hp and due to the turbulence of a big empty can they would likely not gain much due to very poor scavenging of the engine. no bueno, sell them and use the money to do the right thing.

the stainless works headers can be had cheaper now and the obx are around 500 and seem to be OK (like to hear more).

the exhaust needs all the help it can get to let the beast breathe
Yes, ZR-1 exhaust is very restrictive...Well, what do you want for a 27,000 dollar engine option....😜
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Old 08-10-2018, 09:26 AM
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Originally Posted by Rkreigh View Post
I agree

the factory headers on the early cars are tough to modify and the big can cats are tough as nails and it's better to install the headers as suggested. cats really only cost around 5 hp and due to the turbulence of a big empty can they would likely not gain much due to very poor scavenging of the engine. no bueno, sell them and use the money to do the right thing.

the stainless works headers can be had cheaper now and the obx are around 500 and seem to be OK (like to hear more).

the exhaust needs all the help it can get to let the beast breathe
I would also like to know more on the OBX brand... I remember when I had my Z06, people were saying they didnt have the best experience with fit for the LS engines.... I wonder if the fit and quality is improved now....
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Old 08-10-2018, 11:24 AM
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I have SW long tube coated headers, yes they cost more but fit was perfect only modification was the oil dipstick mount that has to be done with any header and after almost 10 years the still look new no discoloration at all. I originally had the tied to a Flowmaster exhaust now have Corsa no drone with ether setup.
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Old 08-10-2018, 03:59 PM
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Yes, I had SW o my 92 several years back.... I didnt have mine coated, but yea, the fit was great and I did the install on my Kwiklift no problem. Just trying to save a buck and was hoping the OBX brand was a decent alternative.
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Old 08-10-2018, 08:59 PM
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Originally Posted by 81c3 View Post
I would also like to know more on the OBX brand... I remember when I had my Z06, people were saying they didnt have the best experience with fit for the LS engines.... I wonder if the fit and quality is improved now....
Some people get lucky with OBX by not having to do much to make them fit right. It's a crap shoot. But if determined, you can make them fit. I would just go SW.
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Old 08-11-2018, 10:51 AM
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RossGN
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Bill

May be going back to stock on my '94. If so, will be selling SS headers and B&B 3" exhaust. B&B shows its for 92-95, so not sure of fit.
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Old 08-11-2018, 12:01 PM
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I have OBX headers, Flowmaster cats and an OBX exhaust. Fit and finish on the headers was shockingly good, if not down right excellent. I know several people with OBX headers, all fit perfectly with the exception of having to dimple the #1 exhaust pipe to clear the steering shaft. I understand that is not unique to the OBX brand. There is no drone from the exhaust and the tone is deep and mellow unlike a Corsa. Here’s what you get at a very reasonable price.
H


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Old 08-11-2018, 04:45 PM
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Originally Posted by ccmano View Post
I have OBX headers, Flowmaster cats and an OBX exhaust. Fit and finish on the headers was shockingly good, if not down right excellent. I know several people with OBX headers, all fit perfectly with the exception of having to dimple the #1 exhaust pipe to clear the steering shaft. I understand that is not unique to the OBX brand. There is no drone from the exhaust and the tone is deep and mellow unlike a Corsa. Here’s what you get at a very reasonable price.
H


I have OBX as well on my 91....Fit wasn't the best...I could tell when I got the labor bill from my mechanic.....I'm like, really man? He does the right thing for my every day car so it is what it is..For 500 bucks you can't go wrong...

I think SW headers are around triple the price..
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Old 08-11-2018, 05:28 PM
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Is there a SW or OBX version that has fittings for the AIR system or is it best to just remove everything?
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Old 08-11-2018, 05:43 PM
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Originally Posted by billschroeder5842 View Post
Is there a SW or OBX version that has fittings for the AIR system or is it best to just remove everything?
I just removed it all. Unless you need it to pass emissions don’t bother. The only thing special I did was to have the exhaust fully welded to eliminate leaks and muffler movement. I’m extremely happy with the set up. Especially for the price difference to a SW with a Corsa. Here a pic of them installed on the new engine.
If I had to do it over again I would have had them coated or wrapped.
H



Last edited by ccmano; 08-11-2018 at 05:45 PM.
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Old 08-11-2018, 09:13 PM
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Originally Posted by ccmano View Post
I have OBX headers, Flowmaster cats and an OBX exhaust. Fit and finish on the headers was shockingly good, if not down right excellent. I know several people with OBX headers, all fit perfectly with the exception of having to dimple the #1 exhaust pipe to clear the steering shaft. I understand that is not unique to the OBX brand. There is no drone from the exhaust and the tone is deep and mellow unlike a Corsa. Here’s what you get at a very reasonable price.
H


Hey Hans...
Those look to be coated or chromed? They look pretty good aesthetically anyway. Did you need wire extensions for the O2 sensors? I think I had to get some with my SW headers IIRC.... Would band type clamps work? I sold my welder a few years ago... so I cant really weld them up. I have an X Pipe in place of the resonator and aftermarket mufflers that I cannot figure out what brand.... no numbers, no name on them.... nice though, polished stainless and they sound great really....Id kind of like to keep the air injection system
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Old 08-11-2018, 10:22 PM
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Yes you need to extend the 02 wires, SW sells the with and without AIR hook-up.
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Old 08-28-2018, 12:18 AM
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Originally Posted by billschroeder5842 View Post
Has anyone ever "hollowed out" the cats on their stock LT5 exhaust manifold?

I'm doing my usual angst about exhaust upgrades on my 91 ZR1. I wondering how hollowing out the cats make a difference and if anyone had any experience with it.

I'm just curious....
having had a 91 zr-1 I recall in the zr1net a few folks with the 90 and 91 cars had reverse catalyst ingestion. The material inside the cat would disintegrate and get sucked back up into the motor causing catastrophic failure.
93 and on had a design change preventing the ingestion. If yours is a 90 or 91 running with original cats I would hollow them out or replace them.
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Old 08-28-2018, 11:49 AM
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Originally Posted by 81c3 View Post
Hey Hans...
Those look to be coated or chromed? They look pretty good aesthetically anyway. Did you need wire extensions for the O2 sensors? I think I had to get some with my SW headers IIRC.... Would band type clamps work? I sold my welder a few years ago... so I cant really weld them up. I have an X Pipe in place of the resonator and aftermarket mufflers that I cannot figure out what brand.... no numbers, no name on them.... nice though, polished stainless and they sound great really....Id kind of like to keep the air injection system
The workmanship on them was first rate. Beautiful welds and transitions at the header flanges. The finish is a high polish. They came that way. I would have them coated if I had to do it over to cut down on the heat. An extension is needed on the passenger side O2 sensor only. The clamps they come with are crap. Ended up with band clamps from Summit. I didn’t use the fake cats and installed real flowmaster cats. As a result it required a little fabrication to mate to the OBX exhaust. Not a big deal. When everything was in place I had the whole exhaust system welded to eliminate the clamps. The only clamps on there now are the band clamps on either sid of the cats. I’m very happy with the whole thing especially for the price. Not to mention I have no resonance.
H

Last edited by ccmano; 08-28-2018 at 11:51 AM.
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