Short question:
Are the manifolds different on an N10 car, and if not will a single-cat y-pipe bolt up to them?

More background:
The PO of my car hacked the living daylights out of the cats to gut them. Essentially they cut open the body of each, gutted them, then welded them back together. So, I'm left with leaky stinky exhaust.

In an ideal world I'd do a full exhaust with headers and a new cat, but that's not in the toy budget right now. I need an interim solution to stop the leak and get a functioning cat on the car. My thought was to source a stock single-cat pipe and one of the less expensive universal cats from Summit etc. and make it work.

Any other possibilities within ~$200?
I supposed I could cut out the existing cats and weld in 2 of the universals, but I need to get under it for a closer look before I can determine how feasible that is.

 

TPI H.O. single cat and TPI H.O. dual cat exhaust systems use the same exhaust manifolds and passenger side H.O. spacer.

If the butchery of the factory N10 system is only to the convertors then you can cut them out and weld in the proper Magnaflow replacement convertors.

Magnaflow 94016 Universal Federal (Exc.CA)

At this time they are $137.00 each and the site has a 20% off promo code with FREE shipping.

 

What is HO? never heard of TPI referred to as HO.

 

What probably happened, and I'm dealing with this too. The outer CAT starts rattling. It just rattles around after 80,000 miles, or 25 years.
Mine is intermittent, so I'm just dealing with it..
But he probably gutted them to stop the rattling.

If it really stinks, you're running rich. Maybe you can lean it out a bit. Bigger TB, etc. But the ECM will probably adjust.

 

Thanks good info, I may go this route. Also curious about the HO TPI reference.

Everything is stock AFAIK, not sure how it would be running rich unless the O2 sensor is going? But yes it's pungent!

I also found a set of used Hedman headers and ypipe on FB marketplace. That plus a $100 universal cat would probably get me what I need.

 

Check the BLM's.

 

If the car is still mostly original, I’d get the stock replacement cats for the N10 Y-pipe and have them welded in. If you still have emissions testing (isn’t NJ strict like CA?), that might be the best way to go. Cheap headers and Y-pipe with a universal single cat might be less effort/cheaper. However, if you ever decide to sell the car someday, having the original parts or equivalent replacements is better for max value over the long term.

 

I've not gone down this rabbit hole yet...

It's a slippery slope. OBDI cars are exempt from inspection, though still required to maintain the emissions equipment. As it sits now, I'm not compliant w/ gutted cats. I'm not too concerned w/ maintaining the stock setup. I'd just rather spend minimal money to fix the problem short-term, but willing to spend more for something aligned with future plans (i.e. headers). But going all-out on exhaust is also not an option at the moment.

 

The Magnaflow Federal Catalytic Converter I posted above are not legal for sale, installation or use in the states of California, Colorado or New York. They meet all Federal EPA requirements.

The states of California, Colorado or New York have decided that replacement catalytic convertors must meet California's emissions requirements and have a C.A.R.B E.O. number even if your car was factory built to Federal EPA emissions standards.

The price of the C.A.R.B. compliant catalytic convertors will make you fall over dead.

Below are the Federal EPA compliant Magnaflow catalytic convertors I linked above installed on a 1990 Formula 350.

The intact but rattling OEM GM "AC" catalytic convertors were sold to the recycler for more than twice what was paid for the brand new Magnaflow replacement catalytic convertors I found on eBay that some random dude had for sale at half normal price during the height of the Covid-19 madness. Rhodium was around $29,800.00 an ounce at the time. Yes you read that right. I didn't make a typo. Almost 30 thousand dollars an ounce. What is Rhodium and Why is it So Valuable?


Magnaflow replacement cats welded in place of the factory OEM GM "AC" cats on a 27k mile 1990 Formula 350.




27k mile factory muffler starting to rust at the seam.

This same job was then done on a 1989 Trans Am GTA ASC convertible with the L98 engine with N10 dual cat and then on a 1991 Firebird Formula LB9 5-speed N10 dual cat car

 

H.O. = High Output

GM referred to their Tuned Port Injection engines as High Output in multiple pieces of factory literature over the years.

I'm referring to TPI H.O. exhaust manifolds, passenger side H.O. EFE valve bare casting used as a spacer or the later H.O. spacer that looked like a cast iron donut gasket, and H.O. exhaust system as based off the L69 5.0L H.O. exhaust manifolds, passenger side H.O. EFE valve, and H.O. exhaust system.

All 1985 to 1989 TPI engine F-body cars had a H.O. exhaust system from the cast iron manifolds to the tailpipes either single cat or N10 dual cat. Even the 1986 to 1989 LB9 TPI low output engine with the "peanut cam" with automatic transmission had a H.O. single cat exhaust system.

That changed for 1990 and newer TPI F-body cars. All 1990+ LB9 TPI engines were High Output and had the hotter camshaft that was also installed in the L98 TPI engine. That changed from 1987 to 1989 when there were two LB9 TPI engines. The low output LB9 "peanut cam" engine and the high output LB9 "hot cam" engine.

For 1990+ LB9 TPI engines if the car didn't come with the N10 dual cat high output exhaust system it came with the L03 TBI low output single cat exhaust system.

All 1987 to 1992 L98 equipped F-body cars had H.O. exhaust systems. 1987 to 1988 had the single cat. 1989 could have either the single cat or the N10 dual cat. 1990 to 1992 had the N10 dual cat.

For 1990+ the H.O. single cat exhaust system went away.


Low Output LG4/LU5/L03 driver side cast iron exhaust manifold on the left vs. High Output L69/LB9/L98 driver side cast iron exhaust manifold on the right.

The manifold on the left has an outlet diameter of just a hair over 1 7/8" and the manifold on the right has an outlet diameter right at 2 1/4".

I'm getting tired so I'm going to post this now before something happens and I lose my reply. I will probably edit this reply to be more clear, correct mistakes, or add more information later on.

 

Thanks @Airwolf , great info!

 

After ‘89, all L98’s got the N10 exhaust.

 

There's a local FB listing for an N10 setup but we're not going to meet anywhere close on a price we're both happy with.

I'm torn between the magnaflows linked here and welding a single cat into the used headers I found on FB. I did some measuring and the pipes are 2.25 but flare up to 2.5 OD as they go into the cats. It's also going to be a challenge given the bend right at the inlet of both cats. Borrowing FB guys pic below.

It's a gamble with the used headers. I'd hate to get it all together to find that it's got a warped flange or something. Also, hacking into the stock y pipe seems like a lot of work for a temporary fix, plus I know it's highly likely I snap off a stud in the stock manifold.

Either way, I'm learning how to weld. I'll have to do some practicing of course!

 

If that's the Long Island guy, I told him he's nuts. Both CATs are bad at this age. No scrap yard can take convertors anymore. It's certainly not worth the $1,000 he's asking. Not even worth a $100.
You can buy the aftermarket Y pipes which are round, not crushed. He has been advertising it for years.

 

If it’s just the cats that are bad, I’d just replace them with the Magnaflow versions listed above. Even if you got a used Y-pipe with cats from someone local, you don’t know if the Y-pipe was dropped, stored improperly, or how many true miles are on the cats. The Magnaflows will put you slightly above your budget, but new cat converters offer the longest lasting solution IMO.

 

Sure is! I offered him $200, no way in hell he's getting $1000. I did point out Hawks has the magnaflow replacement on eBay for $550

 

Mine are hollowed out. I'm hesitant to put too much into the stock pipes as a temporary solution, but I may just do it.

 

I offered him $100. But that was before I knew the outer pipe on the N10 is concave!!!
Now I wouldn't even buy it. I'd go aftermarket.

 

89-92 Camaro/Firebird 305/350 V8 Dual Cat Y-Pipe Stainless Steel - Hawks Third Generation

I would do this, rather than spend $500 on a dead N10 from FB MP.

 

I agree, but for me that's too much $$ for something I will replace with headers at some future time.

 

I'm assuming your N10 is rattling. Try removing the AIR. Mine stopped rattling after removing AIR.

 

No it was gutted and is now leaking.

 

Have it welded. It was gutted because it was rattling. Probably the outside CAT.

 

It's already had a hacked up weld job. They peeled open each cat like a sardine can then welded them shut again.

I just ordered 2 of the 94016 cats from hottexhaust.com, I had to throw in a new magnaflow muffler to get the 20% coupon. Gotta spend to save!

 

Please post pictures of the hack job. I was considering doing the same. I tried getting through the CATs with a sewer machine. Not too easy....

 

I'll snap a few next time I'm under the car, might be a while though.