Hello,

I just bought a 1990 gta 5.7 350 v8 from someone in my town.
He told me that the car had dual cats on it. It has no cats on it now
and the tube that went into the cat is blocked off with a screw.
I have a few questions about this:

1. Will this throw a code in the vehicle?
2. Is there any way to verify the car actually had the dual cat setup?
3. Can I just use one cat (I want it to be emission legal)?

Any help/suggestions would be greatly appreciated!!!!
Thanks!!!!!!!!!!

craig

 

1. It won't throw a code, but it will fail a visual.
2. All the '90 GTAs had dual cats.
3. To use one cat you'd have to somehow install it into the intermediate pipe very far from the motor. Light-off wouldn't occur until the engine was driven for lots of miles. Not the best for the life of the cat.

Catco sells a bolt-in setup w/dual cats. I got mine at Summit.

 

I don't believe that's a true statement.
I disagree. You could put a single cat in the same place the dual cats were. In fact, all factory cats are located in the same place relative to the engine on 3rd gens; so, whether single or dual, they are going to "light off" the same.

You would need a "Y" to join the two pipes to the inlet of the single cat, that's all.

 

Oops! 673 of 884 1990 GTA's had the N10 Dual Exhaust.
OP should look at his build codes (in the center console) Look for N10 code

Yeah, but it seems like you'd be spending bux on labor just to save sixty bux on a Catcon
I'd just get the Catco bolt-in.

 

Depends upon what was done to remove the cats.

scorpion, what does your exhaust look like where the two sides come together? Or, to put it a different way, where do the two banks come together? If two pipes were put in where the cats were, then it might be simplest to just put two cats back in.

 

the dual cats will flow better than one, theres no y pipe each cat is for each manifold then i would y it and run 3" all the way back after that

 

There is one cat bolted right onto each manifold - correct.... but there is still a Y-pipe. The Y-pipe is AFTER the cat converters on a dual-cat setup. Its not a real dual exhaust setup like the RPO description might lead one to beleive. Its set up similarly to the LT1 4thgens, thought not identical.

 

Any one have a pic of this dual cat I might be considering it for my '86

 

https://www.thirdgen.org/forums/exha...k-systems.html

Look at the last post in that thread, I posted pics I took of my dual-cat setup when it was stock, when I first bought the car.

 

More of an "F" pipe. . .

Early in my 3rd gen days, I had a bud who kept telling me to go dual cat. "It's worth 10 HP," he kept saying. Well, true for factory cats, but anything you buy these days will be high-flow, so the advantage is reduced with dual 2-1/4" vs. single 3". Dual 2-1/2" might be slightly better than single 3", but that isn't the factory dual cat size.

 

MY 91 Z has the factory dual. The individual banks ran into two cats under the passenger floorboard, then y'd after the cats to a single pipe running to the muffler, where it then split into to two pipes back to the tips. I've only been able to put OEM replacements in, but I think Random Technologies makes some high flows for f-bodies. Might check Year One.

 

As already stated:
No reason to "settle" for OEM.

There have been reports that OEM replacement is even high flow now.

 

I love how some people think dual exhaust is SOOOOO much better than single exhaust, yet they think dual cats are worthless.

 

Sometimes cash restraints can force you to settle. For awhile.

 

Thanks for the info. I will look for the codes and I can go from there.

 

By "OEM", I meant GM parts, and I assumed that's what you meant. However, rarely if ever are GM parts less expensive than aftermarket.

And, aftermarket, even if "OEM fit", will be high-flow.
----------
The factory dumped them into the same size cat-back as they did single cat, so the difference then was the design of the cat bed. Even if your dual cats are 2-1/2", you're probably dumping them into a single 3" cat-back as well.

But, who is going to volunteer to do a back-to-back dyno or track comparison????

 

2 cats dumping into one three inch pipe is a waste of money. True duals front to back would be of some benefit on a high horsepower motor. A single cat three inch exhaust is more than adequate for a bolt on third gen.

 

2 cats dumping into one three inch pipe is a waste of money. True duals front to back would be of some benefit on a high horsepower motor. A single cat three inch exhaust is more than adequate for a bolt on third gen.

That's good news. I checked for a dual cats system and it was $300.
So I will just go with the a single cat.

 

Nope, I'm running dual 2.5" cats into a 3.5" cat-back exhaust. Do you think GM rated the dual-cat cars 10 HP higher just because it sounds good? 4 cylinders into two cats is better than 8 cylinders into one cat. That's my opinion and I'm sticking with it.

 

No, I believe the dual cat cars put out more HP than the single cat cars. But, you're doing it different than they did; with products available to you that either weren't available during production, or that the factory chose not to use due to cost etc. Which goes back to my previous cat bed comment, and why dual 2-1/4" would perform better than single 2-3/4" (aka, 3"), even when followed by 2-3/4" exhaust.

Dual high-flow 2-1/2" into 3.5" cat-back will certainly support more power than single 3" high flow into 3" cat-back.

We really are in an apples-&-oranges discussion here.

 

I have a dual cat setup but I cut the cats out and had straight pipe welded in place with the y pipe in front going to a 3in catback. It actually worked out pretty good. scorpion I still have the two high flow cats from catco so if you want to save some money and go with a dual setup I will give them to you for free, you just have to pay shipping. They are in good shape still with only around 4,000 miles on them.

 

Everyone is entitled to their opinion for sure. The 10 hp difference was due to having the two cats for sure BECAUSE CATS OF THOSE DAYS WERE VERY
POOR FLOWING. Today you can have one 3 incher flow better than two of the older designs did. The cars were identical otherwise.

 

I can't believe this. This thread and others with the posts that one catalytic converter flows just as well as the two catalytic converter system. Dream on guys.

 

you did not read it right. one high flow is better than two OEM. But i would think two high flows would be better than one high flow and it is. Remember the old 350 H.O. conversion? well dual cat conversion was part of it.

 

I dont follow you. What am I doing different from the factory? I have headers and a dual 2.5" mandrel-bent y-pipe with dual 2.5" high-flow cats into a 3.5" collector. The factory had manifolds into a dual 2.25" crimp-bent y-pipe with dual 2.25" stock cats into a 2.75" collector. Other than the mandrel-bent pipe, my system follows the same shape as the factory, its just larger diameter. I would think if the factory dual-cat system flows better than the single cat system, then my larger setup should flow more as well.

However, the factory single cat system is poorly designed, especially on the 305 cars. Its more like a T-pipe than a y-pipe. If you have a redesigned y-pipe that is truely a Y, into a 3" cat, that will flow a hell of a lot better than factory. Whether its better than an upgrade dual-cat setup, I have no idea for sure. But I'm still sticking to my theory that 4 cylinders flowing into 2.5" is better than 8 cylinders flowing into 3". With a single cat system, you're doubling the number of cylinders but only increasing the pipe size 20%. (half an inch is 20% of 2.5 inches)

 

okay simple version two high flow cats are the best setup. If you can only afford so much then get one high flow not two OEM cats.