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Old 10-09-2013, 06:53 PM   #1
L98auto
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Default Deleting Pre-cats

I have a 2.5" catless front Y-pipe for my '86. Will I be able to run my stock main cat (with AIR tube) without fear of it melting down since the pre-cats aren't "helping" anymore? If, in the future, I run a high-flow cat without a AIR tube, will it be safe from meltdown too? Thanks.
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Old 10-09-2013, 09:38 PM   #2
Phosgene
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i dont mean to hijack thread, but similar question related to cats
could i remove my main cat (take it off and gut it) and reinstall it empty with no issues to the pre-cats
i dont have to do emissions here, so im not worried about that
also if i delete the AIR pump, what issues could this cause?, is it possible to delete the air line to the main cat alone if it was to cause any issue
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Old 10-09-2013, 09:44 PM   #3
ghoastrider1
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I am in the middle of replacing my tranny. When doing that, one must drop the exhaust system. When I dropped mine, the main cat was almost hollow. Its was, for all intents, gutted. No codes where thrown. ran great, sounded great. Putting it back together with long tube headers,true duals and high flow cats.
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Old 10-09-2013, 09:47 PM   #4
Phosgene
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what about the AIR pump?
from my understanding if you dont delete the air pump also (or if there is an exhaust leak) it will cause backfiring, or was that way on my 5.0HO (mark vii)
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Old 10-09-2013, 09:50 PM   #5
ghoastrider1
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Quote:
Originally Posted by Phosgene View Post
i dont mean to hijack thread, but similar question related to cats
could i remove my main cat (take it off and gut it) and reinstall it empty with no issues to the pre-cats
i dont have to do emissions here, so im not worried about that
also if i delete the AIR pump, what issues could this cause?, is it possible to delete the air line to the main cat alone if it was to cause any issue
The air pump is hooked up to tubes coming off the exhaust manifold(s). there are vendors on here selling "delete" air pump bypass systems. They run about 130 bucks and you need to by a new belt. It gets rid of the entire air pump system. It will not throw codes.
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Old 10-09-2013, 10:00 PM   #6
Phosgene
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Quote:
Originally Posted by ghoastrider1 View Post
The air pump is hooked up to tubes coming off the exhaust manifold(s). there are vendors on here selling "delete" air pump bypass systems. They run about 130 bucks and you need to by a new belt. It gets rid of the entire air pump system. It will not throw codes.
so if i delete it before the manifolds (block the tubes for it), and just run a shorter belt with no air pump, it wont cause any problems, or do i have to use a delete kit? seems like it would mess with the ratio for the oxygen sensor and throw it off
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Old 10-09-2013, 10:57 PM   #7
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huh uh-huh
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To the OP..

yes, you CAn dump the pre-cats without any consequences. The main does just fine without them. There were deleted a couple yrs later anyway...

Running the main without an air feed CAN cause it to fail sooner than normal. The air tube feeds fresh o2 to the catalyst to help keep the 'burn' temp up so it does its job better. It will run for quite some time without extra air, but it CAN do a couple different things depending on your particular engines exhaust quality.

it MAY simply clog as it ages from the accumulation of hydrocarbons that failed to burn-off properly.

or
it might melt down internally and clog from over heating due to rich fuel or oil burning.

Either way, a brand new late model cat will likely last at least several years as long as the engine is in fairly good shape,. Beyond that, there are no issues with the partial d/c of the cat/air system. As long as you don't have to deal with a visual inspection for smog or inspections...if you DO, at least have the parts mounted.
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Old 10-09-2013, 11:09 PM   #8
Phosgene
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Quote:
Originally Posted by leesvet View Post
To the OP..

yes, you CAn dump the pre-cats without any consequences. The main does just fine without them. There were deleted a couple yrs later anyway...

Running the main without an air feed CAN cause it to fail sooner than normal. The air tube feeds fresh o2 to the catalyst to help keep the 'burn' temp up so it does its job better. It will run for quite some time without extra air, but it CAN do a couple different things depending on your particular engines exhaust quality.

it MAY simply clog as it ages from the accumulation of hydrocarbons that failed to burn-off properly.

or
it might melt down internally and clog from over heating due to rich fuel or oil burning.

Either way, a brand new late model cat will likely last at least several years as long as the engine is in fairly good shape,. Beyond that, there are no issues with the partial d/c of the cat/air system. As long as you don't have to deal with a visual inspection for smog or inspections...if you DO, at least have the parts mounted.
what im wondering is if i gut the cat (remove all the material inside) and mount it back empty, will running the air cause backfiring
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Old 10-10-2013, 02:18 AM   #9
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I run a catless 85 front Y and a Magnaflo main cat (no air)

Just had to make some mods to the front pipe flange to adapt the 86 style cat.

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Old 10-10-2013, 11:53 AM   #10
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I also replaced the stock muffs with Borla round tips

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Old 10-11-2013, 01:34 PM   #11
mako41
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Quote:
Originally Posted by Phosgene View Post
what im wondering is if i gut the cat (remove all the material inside) and mount it back empty, will running the air cause backfiring
No the exhaust will just have a little more growl.

But you will have some droning at hwy speeds.
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Old 10-12-2013, 10:44 AM   #12
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I've run mine both ways with no issues. My original pre cats broke up and clogged my main cat a few years ago. I removed the pre cats and gutted the main cat till i could afford to get a new front y-pipe. I took the car to one of our supporting vendors and had them install a new front y-pipe with pre cats and a new main cat. A year later the pre cats broke up again. I caught the rattle early this time so they didn't totally clog the main cat. I then bought two California approved small cats and had them welded in place of the pre cats when I had my custom short headers installed. After I passed smog I removed the main cat, still partially clogged, and replaced it with a straight pipe with a slip and flange just like the cat. So, now I'm running pre cats with main cat removed.
Wish I didn't live in California sometimes.
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Old 10-12-2013, 08:59 PM   #13
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huh uh-huh
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I do not know why a gut-less cat would cause ANY engine issues since that is so far out of the eng op loop...

so no, go for it. Maybe a different tone, noise. I have done it. In Ca I wouldn't do that if you PAID me now...the fine is TOO heavy for removing factory smog stuff...and they monitor with infra red scanners and can tell WHO has cats and WHO is cheating...and those damn cameras...(now with scanners)
Late model mains don't restrict anything. Pre-cats DO but that's a done deal. None of the inspectors know what yr had then and when they went away...cause that changed all the time.
Used to be even in the 90s....you could take a few things off the car, like plates and maybe a passenger seat and go to some muffler shops in the smaller towns like Oxnard or the fringe cities along the LA area and tell then it was going to be an "off road" ONLY car from now on and they would hack it ALL off for you....I'm sure its more difficult to get a shop to do that, especially if you DRIVE it to the store...
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Old 10-13-2013, 10:09 AM   #14
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Quote:
Originally Posted by Phosgene View Post
what im wondering is if i gut the cat (remove all the material inside) and mount it back empty, will running the air cause backfiring
It shouldn't I have long tube headers on my '87 and I have removed the AIR stuff. No backfiring at all.

I would certainly use an AIR delete kit. It makes it much easier to do and keeps the OEM belt routing. But you will need a belt that is about 2" shorter. Remove the AIR rubber hoses at the exhaust manifolds and use a 1/2" pipe cap (pipe thread cap from any hardware store) for the valves. Disconnect the two wire harnesses and remove all the components. No codes will be set.

A couple years ago, I bought a front Y-pipe with out the pre-cats and I had to re-bend parts of it to fit. It never did seal properly. Once I started to use the car primarily for autocross and track days, I decided I wanted true duals. Most shops will not remove cats and install duals.

So I removed the entire exhaust system, removed the license plates, trailered the car to a muffler shop and told them the car was for "off-road use only". They happily installed a 2-1/2 dual system. I provided the mufflers (Walker DynoMax race mufflers) and the car has no interior resonance and is actually quiet at freeway cruising speeds.
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Old 10-13-2013, 08:08 PM   #15
jsinga
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It won't backfire unless something else causes it. My bone stock gutted pre cats and main cat work just fine. The fix for a plugged main cat from broken pre cats. 0. Garenteed it will be loud.

JS
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