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Sajeev
Community Manager

The Underappreciated Catalytic Converter?

Check out this video and note that a new Hellcat makes 707hp (SAE net, not SAE gross) on catalytic converters.  I think when you see how far cats have evolved, what benefit they give, it's real easy to love them even if you are a performance junkie.  

 

I always go back to the Hellcat's 707hp when people with not-racing cars talk about removing their cats, because odds are they will never make enough power for cats to be a restriction.  My last such argument was the most obvious: with a guy with a 150hp Lincoln Town Car, and I had to apologize for laughing when he said he was gonna remove the cats so it will go faster. (owner is a nice guy, just unaware of other issues like a 50mm throttle body, 14 lb/hr injectors, and terrible heads/cam that make his plan impossible.) 

 

And if you have an older vehicle with 2-way or early 3-way cats, just upgrading to an off-the-shelf modern cat will outflow your engine for years to come.    Tell me what you think of this! 

 

 

https://www.youtube.com/watch?v=Jj-ufVglr6M

 

 

20 REPLIES 20
Pepperalls
Detailer

I personally find this really interesting. At times I have faced "the environmental comments" when driving an older vehicle to school or work. A bit of performance loss is situational... it wouldn't matter a bit (if I put cats on) in some of the rides I have had because they just cruise (I'm not racing). I would enjoy being able to use the rebuttal of "yeah it's a 66 inline six but has a 2017 cat system and blows cleaner than your 2011 Honda". Maybe that isn't a realistic goal.

 

But a how-to article/video that showed how to properly apply a modern cat and such to older configurations would be interesting.

 

-something 50s or earlier (pre pcv valve and limp factory performance)

-60s carb keeping the carb

-old engine with modern efi

-maybe even early efi gen1 cat era

 

Besides, there may come a time that this might become a compliance piece to drive old cars in some places. Some DIY as an option than having to do a compliant engine swap makes sense to me.

Greg_I
Detailer

Admittedly, I am guilty of removing the cat on a few older vehicles I have owned in the past. Mainly as a cost savings move for dealing with a plugged bead type unit. Here in Michigan there's no emissions testing, so there's no enforced penalty for removing it. That said, I agree that there is little to no real benefit for removing it, I think for anyone worried about a restrictive exhaust, changing the muffler will allow for better results, however I think that exhaust technology in general is quite good these days. The only reason to swap a muffler on a new vehicle is for sound purposes.

Sajeev
Community Manager

Great feedback @Greg_I @Pepperalls as I think many opinions would change if information on 1) "upgrading" a pre-emissions car to a modern cat (might be harder than expected) and 2) dyno testing an all original malaise-era car with a modern cat to see how much power it picks up, and if it gets any cleaner.

 

Of course with the malaise era cars you will also need to upgrade the cam/heads/pistons (many had deep dishes for low compression) to take full advantage of the better tech. And pre-emissions vehicles might need some modifications to keep a cat from melting...who knows. 

 

 

56Tiger
Pit Crew

I had a 1989 Town Car, with the same 150 hp 302 you described. At 180,000 miles, I removed it and installed a Mustang 225 hp 302. Was it a race car? No, but it was noticeably quicker. One of the best cars I have owned! 

DougL
Intermediate Driver

I don't think that installing a catalyst on an older vehicle is realistic. The catalyst requires very tight fuel control that just does not exist on pre emissions vehicles. I expect my 53 Mercury flathead would plug up a modern catalyst in short order. A modern feedback fuel injection system would be required, at a minimum. Upgrading an early catalyst to a modern catalyst is much more realistic.
Ducknuts
Pit Crew

I had a Ford Fiesta in the early 80's and replaced the catalytic with a straight 'tester' pipe. That made that little car run much better and it would still pass emission tests. The only problem was that if would backfire under certain circumstances and it sounded like a rifle shot going off. I don't really know about the performance of the newer cars  and the effect of the catalytic, but you don't see them on race cars.

Sajeev
Community Manager

Go test drive a 400-700hp car sometime, they are amazing. And they have cats. 

DougL
Intermediate Driver

FYI, in Europe, many race cars are required to have catalysts.
MichaelD
New Driver

The only problem have with the (mandatory) cats here in Calif is the price! but as the saying goes--how much horsepower can you afford~~~
gudsplr
New Driver

When I encounter someone complaining about catalytic converters I wonder what air they breath.

In 1965, in the SF Bay area, I and friends had to stop playing tennis because our lungs and chests hurt so badly from the smog.

I prefer having catalytic converters and being able to exercise outdoors to having no catalytic converters and staying inside because it is too painful breathing outdoors.

Possibly those that remove the catalytic converters from their cars have the little oxygen bottle breathers with them.

TG
Detailer

Most of the folks I know start talking about bypassing cats when it comes time to replace them... due to the relative cost compared to the rest of the exhaust system. The cost of the cat is easily half of the price of a new exhaust

The problem with cats and older cars, as indicated by some of the other responses, is that if you do not have optimum mixture, it will cause performance robbing backpressure

Its nice to know that a well tuned modern motor can make 700 hp on cats, but I won't be putting them on my carbureted 454 vette any time soon

CongVu
New Driver

I had a Ford Fiesta in the early 90s and replaced the catalyst with a straight 'test' tube. That makes that small car run much better and it will still pass emissions tests. The only problem is if it backfires in certain cases and it sounds like a rifle shot. and I think I'm playing a fierce battle game like this Friv 2 Games

JimR
Instructor

Keeping the cat isn’t always the best choice either.
I have a forced induction, EFI rotary from the 90’s. It came stock with not one but TWO cats in an effort to improve emissions. The first cat...or “pre-cat” was suppose to help cold start emissions but had some history of collapsing under the higher EGT and pulse energy from the rotary. So most responsible owners removed it. That also instantly improved performance in quicker spool-up and power. The main cat wasn’t an issue but they do have a lifespan. I think most of us over time moved to a modern quality hi-flow ceramic matrix cat. Better performance, better sound and no stink.

 

 

Was in SF Bay Area not long ago. I wished I’d had an oxygen bottle then...but not because of vehicle exhaust fumes. And I wouldn’t have wanted to play tennis in it either. 

Sajeev
Community Manager

Yeah Rotary engines are a whole different ballgame.  

JimR
Instructor

They are definitely different. But it’s not just b/c it’s a rotary that it can be (imo) alright to remove a cat. With any forced induction engine good exhaust flow is critical and removing a cat, or at least moving to a modern design can help a lot. Especially if there was little to no change in system design from the n/a to f/i versions of a particular car. 
But then there’s no free lunch. Removing a cat comes with stink, sound and usually a need for tuning...not to mention hassles if you have testing. 

Sajeev
Community Manager

Modern cats can easily handle forced induction.  The Hellcat is a good example of the technology at work. 

JimR
Instructor

A key word there is “modern” and new cats. 

Guitar74
Technician

The new cats are terrific. But asking my 50 yr old car to perform within the parameters of them is unrealistic as the mixture target is ever changing and carburetors are demand devices. 

 

Here's my take on it:The modern technology at work with the Challenger and many new cars that allows them to make that kind of power through a restricted exhaust is amazing. Will I be trying to adapt it to my classic cars? No. Here's what I WILL do for the environment. I will keep my car in a state of tune that allows it to burn much cleaner than it probably did thanks to electronic ignition, tuning my advance curve, tuning my fuel curve for the octane (although that can be ever changing as different stations do different things to arrive at a said octane rating) and properly carbbing each car for what the engine actually demands. Remember "leaner is meaner" meaning that an overly rich car won't run as well as a slightly lean car will. I will also always run my vacuum advance to make sure that my mixture is completely burn at part throttle. 

 

By and large "emissions" is a gentleman's agreement between most municipalities and corporations, mass transit, etc., in that each car that passes gives these places a credit for more smokestack emissions. As long as I still get stuck behind MARTA buses that spew black smoke into the air from their improperly tunes diesel engines, then I am giving myself a pass on not running cats on my exempt cars as I am CERTAIN that they are doing way more harm for the enironment than my "tuned classic cars". For that matter so are the improperly tuned, and maintained late model efi cars.

 

 

 

 

Sajeev
Community Manager

You have a real good take on things. I still would like to think that 1974-1980s cars would perform a lot better when newer cats installed on them, and I bet they drive/idle better with new style cats too! Well, a kid from that era can dare to dream, can he? 

Guitar74
Technician

Hey, dreaming feeds the innovation that feeds progress. Nothing wrong with dreaming. It's completely off topic, but what if the young Jimi Hendrix, Les Paul, or Eddie Van Halen didn't have a dream and follow it? I know MY guitar playing would suffer from it from having a bar that wasn't set quite so high for everyone else that followed.