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C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

remove cat or precat?

 
Old 07-15-2013, 01:34 PM
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MatthewEdward
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What would give me the best performance, removing the main cat and keeping the pre cat, or keeping the main cat and removing the precats? What would the sound difference be? From what I hear, the exhaust on the l98 is very restrictive and this should help it breath better
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Old 07-15-2013, 01:56 PM
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The stock cats on your car if they are stock are junk anyway.

If you have to get a smog or visual safety inspection for that yr in your state you HAVE to have SOMETHING.

The cats are not the problem with the exhaust. The exhaust is. The whole system...Mostly the manifolds themselves. That's the worst part of the system. seriously. The stock ex manifolds block half the ex port. After that its at least 2" all the way. AT the port its more like 3/4".

BUT,
Here is what you CAN do without getting in trouble AND get some improvements...

Buy a new front Y-pipe. Minus the pre-cats. Those are corks. 99% of all inspectors do NOT know if they are supposed to be there or not...so as long as there is a MAIN cat it will not get you busted.
Go spend $100 on a new design main cat, new front Y pipe and then start saving for a Cat-back system for the rear. That's where the sound comes from....

loosing the pre-cats will get you faster revving and better throttle response.
You're going to have to keep one...most shops will NOT remove them all due to jail time, beatings by the state inspectors and severe fines. They will remove the pre-cats if you buy a new main from them and tell them the new front Y pipe is the factory upgrade.
Or do what I did...take it on a flatbed and tell them its no longer a street car but a dedicated track car....OFF ROAD ONLY. That story has to be believable though...if you sell it then you can have a shop install whatever you want. Its a tough sell if you drive it to the shop.

It WILL pass a smog with only a main cat.
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Old 07-15-2013, 02:05 PM
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I just went to the shop and told him its for off road use and he smiled and said ok, he said he will remove the cat for 60 $ and all of them for 200. Headers are out of my budget right now but I will get them soon. Thank you for all your info! Helps alot. I wonder if they can just punch out the precats?
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Old 07-15-2013, 02:16 PM
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sure....
punch out the pre cats and the main. I am a FIRM believer in giving the gov what they want. Never screw with the people that can make life difficult. As long as they SEE a cat they assume that it IS a CAT. Until you have to TEST...seeing a cat is good 'nuff.

Empty? maybe so..but it LOOKS legit.

The hot ticket for a budget upgrade is a set of LT exhaust manifolds. Go find a set of those to stick on your L98 and it is a big improvement. The port problem is resolved and things get better instantly. The LT ex manifolds fit too....just like the L98 stuff.
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Old 07-15-2013, 02:44 PM
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Lt1 manifolds? Thats a great idea! Im going to the junk yard asap! And yeah they are screwing us, so screw them! At the shop now, gonna get them all punched out and maybe the mufflers too lol
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Old 07-15-2013, 03:27 PM
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Haha you won't believe what happened. They got it jacked up, and there are no cats on it, has the x pipe or whatever and has dynomax mufflers. Lol just saved me some money. So whats left to upgrade? Just long tube headers?
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Old 07-15-2013, 03:30 PM
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Originally Posted by MatthewEdward View Post
I just went to the shop and told him its for off road use and he smiled and said ok, he said he will remove the cat for 60 $ and all of them for 200. Headers are out of my budget right now but I will get them soon. Thank you for all your info! Helps alot. I wonder if they can just punch out the precats?
If you are going to install headers, you may want to wait on everything until you get them and they are installed. At that point, you can finish the rest of the exhaust and go with true duals. If you are going that route, then why spend a couple hundred on just removing the cats? Does the shop have a tube bender? Somebody with experience with tube benders can create a complete system in about an hour.

I just installed a set of Hedman Elites in my '87. It already had true duals and an X-pipe. I'm using DynoMax Race Mufflers and surprisingly the car is quite at cruise speeds. But at WOT, it is fairly loud. I would suggest you be wary of using Flowmasters; many people have reported that there is a lot of interior drone with the 40 series, and the 44's and Super 44's are worse.

BTW, it's always best if you specify the year of car as there are differences....
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Old 07-15-2013, 05:54 PM
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Originally Posted by MatthewEdward View Post
Haha you won't believe what happened. They got it jacked up, and there are no cats on it, has the x pipe or whatever and has dynomax mufflers. Lol just saved me some money. So whats left to upgrade? Just long tube headers?
ok, so you have a decent exhaust system in place, replace the manifolds with LTs or headers and you're set.

Might wanna look next time...
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Old 07-15-2013, 06:10 PM
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Originally Posted by leesvet View Post
ok, so you have a decent exhaust system in place, replace the manifolds with LTs or headers and you're set.

Might wanna look next time...
Haha I did, didnt see em and though maybe they are hidden some were lol. The cars too low to crawl under. And to the other guy, yeah these dyno maxes are pretty quite at idle. Thats why I thought the cats were still on.
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Old 05-05-2019, 10:43 AM
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In the distant future am thinking of removing all my cats. I have a stick welder and would do it myself, and replace with straight pipes. I already have a cat-back installed by the previous owner.

The thing I am concerned about is noise, the current set up sounds awesome, but it is a little loud and drones on the highway. I am conerned that it will be louder without cats. Has anyone looked at replacing the center cat with a resonator (and keeping the mufflers)? If so how did that work out?

Car is an 89 BTW

Last edited by auburn2; 05-05-2019 at 10:44 AM.
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Old 05-05-2019, 12:06 PM
  #11  
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Removing Catalytic Converters on ANY street driven Car in the United States is against FEDERAL LAW.

Besides if you remove the big one the "drone" will get you....

There are others here who re-installed the big catalytic converter after hearing the drone without it, if it is noisy now, wait until you hear it without that catalytic converter.

I installed a Chambered Exhaust system on both of my Corvettes. I bought them at [email protected] and installed them myself. On the C4 I left the front Y pipe alone with the "Pre-Cats" or whatever they are. I then ordered a new Hi Flow catalytic Converter and installed it in place of the original and connected the chambered exhaust on the car. According to my GTECH Pro the car gained almost 14 hp with the free flowing exhaust and the chambered pipes, not as much as I had hoped for.

Headers are fine just keep the shells of the catalytic converters on the car. You just remove the catalytic and break up what is inside the shell, dump it out and re-install the catalytic converter. I did this for a few months when I could not afford a new VW catalytic converter. If you ask a mechanic to do it frequently they are smart enough to say "no" as there is a big fine (~$10,000) for doing so. The mechanic who helped me with a plugged Catalytic converter removed it and gave it to me. I went out back of the station with a long screwdriver and a mallet, one whack and it all came tumbling out. Then the mechanic installed the empty catalytic converter back into the car and I drove 300 miles home the same day. The mechanic was free of any wrong doing this way. I absorbed all the responsibility for the action.

Removing of the emissions equipment is not a great idea as you will likely have to get a new prom made for your car or deal with a check engine light that stays on.

Both of my Corvettes meet their emissions requirements and both have their equipment fully functional and operating. Here in VA they check for a catalytic and I have seen a suspicious inspector use a laser thermometer and verify the catalytic is still "active". Now here in Virginia they have portable emissions testing stations that look at your exhaust while accelerating on a highway entrance ramp. They take pictures of the car and will send out a 2 week notice to get the car repaired or the license becomes invalid. They don't do this only to Virginia drivers, I know people from Maryland who have received tickets in the mail. Another good reason to keep the car legal is when you sell it, resale of a car without emissions would be hard in this part of the country.

Yes they even check my 1968 C3 Corvette for it's equipment. All I have is the PCV valve and that is it. I am sure the first thing the original owner did was remove the air pump IF it ever had one. I have had a couple inspectors ask me where my A.I.R. pump and hose set is. On a 51 year old car they let me slide on the A.I.R. Pump as I have shiny headers on the car anyway. The 427 cast iron exhaust manifolds that I have had no holes in it for the air pump anyway.

With all my systems working I was able to break the 30 mpg mark and that is using the car the way they designed it, I like it. If I want to scare myself I still have a C3 with over 500 hp coming out of my little 427.

Good Luck with your Corvettes and Enjoy them for all they are, a well designed car with good handling and an incredible body design just a "bit" under-powered.
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Old 05-05-2019, 02:45 PM
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Get a straight through resonator under the car, that will help with drone/straight pipes
If it were up to me I wouldnt run them either and hang LTs on it.

How many 2 stroke leaf blowers are out there creating smog even after laws passed to ban them?
Anyone remember the protests with them literally throwing up the middle finger? Bet we support most of em on top of it.

Freedom of choice, be a leader or follow the rest off a clip. Bahhh....
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Old 05-05-2019, 05:19 PM
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double post

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Old 05-05-2019, 05:24 PM
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Originally Posted by ctmccloskey View Post
Removing Catalytic Converters on ANY street driven Car in the United States is against FEDERAL LAW.

.
That is not actually true. It is against Federal law to remove functioning emissions equipment. It is NOT against Federal law to remove faulty or malfunctioning emissions equipment, including catalytic converters. Catalytic converters go bad and are removed all the time.

Also state laws vary regarding emissions on older vehicles, VA may have a deal with Maryland, and they can probably ticket someone from any state, but they can't have someone's license pulled from another state.

Finally there already is drone with all 3 cats in place. My question is would a resonator do a better job of cutting down on it.
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Old 05-05-2019, 07:15 PM
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Originally Posted by auburn2 View Post
In the distant future am thinking of removing all my cats. I have a stick welder and would do it myself, and replace with straight pipes. I already have a cat-back installed by the previous owner.

The thing I am concerned about is noise, the current set up sounds awesome, but it is a little loud and drones on the highway. I am conerned that it will be louder without cats. Has anyone looked at replacing the center cat with a resonator (and keeping the mufflers)? If so how did that work out?

Car is an 89 BTW
If you’re really worried about “drone” and noise get a high flow main cat but ditch the front 2 pre cats you can get both a 2.5 front y and a high flow main cat from Walker for under $300 that’s a lot of bang for the buck especially if the cats have some miles on them
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Old 05-06-2019, 12:11 AM
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Originally Posted by auburn2 View Post
In the distant future am thinking of removing all my cats. I have a stick welder and would do it myself, and replace with straight pipes. I already have a cat-back installed by the previous owner.

The thing I am concerned about is noise, the current set up sounds awesome, but it is a little loud and drones on the highway. I am conerned that it will be louder without cats. Has anyone looked at replacing the center cat with a resonator (and keeping the mufflers)? If so how did that work out?

Car is an 89 BTW
If you are afraid of noise, won't removing the cats muffle LESS noise and thus louder?
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Old 05-06-2019, 12:16 AM
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Originally Posted by ctmccloskey View Post
There are others here who re-installed the big catalytic converter after hearing the drone without it, if it is noisy now, wait until you hear it without that catalytic converter.

According to my GTECH Pro the car gained almost 14 hp with the free flowing exhaust and the chambered pipes, not as much as I had hoped for.

Removing of the emissions equipment is not a great idea as you will likely have to get a new prom made for your car or deal with a check engine light that stays on.
That is exactly what happened to me.

14 isn't bad. Not sure if the old cats are plugged or just that the newer design is better flowing. That said, the price you pay is the noise you hear.

Why is that? What will trigger a code? There is no exhaust back pressure sensor. There is also no downstream O2 sensor. So why? The ECM won't know.
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Old 05-06-2019, 12:29 AM
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Originally Posted by auburn2 View Post
That is not actually true. It is against Federal law to remove functioning emissions equipment. It is NOT against Federal law to remove faulty or malfunctioning emissions equipment, including catalytic converters. Catalytic converters go bad and are removed all the time.
Are you sure it stops there? I thought there was something that said that a tech is NOT supposed to remove emissions equipment UNLESS replacing it with a working one? I imagine a tech can remove the cat if it is part of the assembly to get at the engine or transmission but at the end of the process, he has to replace it?
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Old 05-06-2019, 02:04 AM
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I had the front Y replaced with 2 1/2" mandrel-bent SS and a Random-Tech hi-flow main cat installed on my prior '88 and it always easily passed the OH sniffer test back when they still required such testing. And yes there was a nice power gain.
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Old 05-06-2019, 08:41 AM
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Originally Posted by ctmccloskey View Post
Removing of the emissions equipment is not a great idea as you will likely have to get a new prom made for your car or deal with a check engine light that stays on..
On 84-95 Corvettes there are some parts of the emission system if you remove that will cause a SES light to come on like EGR but EXHAUST is not one of them 96+ cars will though

Last edited by Y-bodluvr; 05-06-2019 at 08:41 AM.
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