It's time to pass an emissions again, and I don't think it's going to happen. Last year it barely passed. Since then, the AIR pump seized and has been removed. Apparently, it's a one year only part. I would have put another back on, but it was either not available or would go on back order at check out. Also, one of the front converters is rattling.

I am thinking of removing the front catalytic converters and going with a single OBDII type in the rear. Has anybody passed an L98 on an emissions tail pipe test with an OBDII catalytic converter that doesn't have an AIR fitting?

 

I bought an aftermarket catalytic Converter from Summit and it was a "Universal" that just happened to match right up with the C4's system, it even had the air pipe and came with a cap on the end of the tube. The instructions that came with the converter said to cap it off if not needed. I then put a chambered exhaust behind it. The first time I went to get the Emissions tested it passed with much better numbers than previous years. The catalytic converter that I bought had a higher flow rate than the restrictive original design. I paid about $150 for the universal and it has been great ever since. The car gained just shy of 14 hp with the new catalytic the chambered exhaust so in the end I would call it a "worthwhile project".

The front Y pipe has those little bulges in it and I have heard them called "Pre-Catalytic" converters. I am not sure why they are right there in that location because if they were truly catalytic converters they would be generating a ton of heat inside the engine compartment. I would remove them and empty them out and re-install the empty shells so they "appear" to be all there. This should solve the rattling issue once and for all.

Good Luck with your project! Use a decent quality aftermarket catalytic converter and you will probably have no trouble passing the emissions testing as long as everything else is working or tuned properly. If it needed AIR pumped into the catalytic use an aquarium air pump while the Corvette is being tested and removed the minute it passes..

 

Thanks!

 

I removed the pre-cats and installed a y-pipe and main hi-flo cat. I don't have inspections and the car is louder now.

 

I have a front Y pipe with the front flanges cut off.
I can send the front precats so you can weld them back on to your pipes for $65 shipped.
602-510-2519 Chris
Call Larry at 20th Street Auto for the air pump. He just might have a couple sitting around..602-258-2020

 

Move to NJ, Cars 95 and older don't have to be inspected.

 

but then you have to live in NJ

 

I wouldn't do it.....what I pay per month in taxes is equal to a full year in other areas of the country

 

You got me there, but it could be worse, I could live in West Virginia LOL

 

I believe a new hi flow cat will get you through emissions. When I had to take mine through emissions testing it did better without all the stock equipment. Air pump, egr, and precuts removed. New cats are much more efficient then ones from the eighties.

Good Luck

 

Since you are in Tenn based on your profile... why not go Antique plates? Once you get the Antique plates (25 year old cars and older) then you bypass the inspection. Plus, if it is anything like FL, antique plates are cheaper to renew as well.

 

My first 35th Anni had a 2 1/2" mandrel bent Y, Random Tech cat and TPIS cat-back and easily passed the OH sniffer test each time.

 

I drive my car on any given day. In Tennessee, antique plates are only valid for weekends and car events. I'm not worried about a ticket so much as not being covered by insurance for a non agreed use of the car by getting a ticket in an accident. My insurance agent had a client who was denied a claim for delivering pizzas on a personal policy instead of on a commercial one. I recently gave a ride to a used car dealer at a grocery store because the police seized his car after a minor accident. He was using the car for personal use on commercial dealer tags. I talked to an acquaintance who used to be a policeman. They frown on that.

 

FWIW - on my 85, I upgraded and installed an 86-91, walker front Y-pipe assembly. it comes pre-catless, and with a hi-flow main cat. stainless and mandrel bends. nice hardware - no installation issues. as for the smog pump, can't help you there....

 

I bought a roof panel off of craigslist this morning, and the seller also had a working 1986 smog pump laying around in his garage that he had pulled off of his race car. So I picked it up too. I found a shop that will replace all three cats with a single universal.

 

That sucks. In FL there are no restrictions.

 

- no restrictions and $21.50 for plates. it's a win-win....

 

Don't fool around.... The rattling pre-cat will come apart and you will think your transmission is going out. It will fall down and plug up your main cat. The car just won't go, with no power you'll keep mashing the gas and the transmission will shift up and down like a yoyo. Ask me how I know....

 

As a follow up, the car passed.

Set up. 1986 L98
1. No front cats with a single Magnaflow universal in the rear.
2. No AIR pump
3. Engine temp during test at 200 to 220 degrees

Numbers
HC reading of 217
CO reading of 0.38%

The exhaust is noticeably louder with the change to the cats from idle to 3,000 rpm. The exhaust goes quiet after 3,000. The mufflers are still stock. There is a drone that will make a person cross eyed between 1,500 and 2,000. The new setup is causing the floor in the hatch area to resonate. I knocked the edge off the drone and made it tolerable by laying a 1/2" thick rubber mat cut to fit down in the back. With the rubber mat, the car is quiet on the interstate at 2,100 rpm.

 

Congratulations stngry63!

You did it! Good for you!

I need to do the front Y-pipe to get rid of those little "what ever they are's" mounted in the pipes. Was there anything inside the "Pre-Cats"? I would love to see the insides of one to know what they really are. I can't believe that GM would put catalytic converters in the engine compartment due to their operating temperatures.

My wife and I noticed a better sound out of our C4 as I used a Chambered Exhaust but had no serious drone issues with that or the aftermarket Catalytic converter. My emissions numbers went down with the new catalytic converter and I gained 14 hp. You probably got more as you did the air pump delete.

Did your new catalytic converter have the air tube on it? How did you cap it off?

Now you need to test the fuel mileage, after my replacements I started breaking into the 30 mpg range. Mine is an automatic with the special 3.07 rear end ratio instead of the normal 2.55 or whatever they use. I use the C4 for trips around the area and my BB C3 for scaring myself every once in a while.

With your car legal and clean emissions coming out the rear you need to get out there and enjoy your beautiful Corvette on the awesome roads of Tennessee!

Best Regards,
Chris