Catalytic converters on older musclecars

[Later-A-body]

I am looking for anyone that has installed catalytic converters on thier older non emission performance car and what type of results they have seen. I am considering installing dual cats on my 466 inch EFI Pontiac to help reduce emissions and clean up the exhaust. The car is making over 550 HP. Thanks.

[Larry Callahan]

I have kicked around this idea myself for years. It will be interesting to see if anyone else has done it.

[nc69rs]

I have a set of 3" high flow thunderbolts on my camaro. I have a LS2 in the car. I basically put them on to get rid of the gas fume smell. They work great. Smoothed out the exhaust rasp and quieted it down a bit. I didn't notice any HP lose.

[Later-A-body]

That was my main reason why I wanted to do it in regards to the exhaust smell. What brand of cats did you use. Did it quiet the car down as well?

[BonzoHansen]

I had to take the cats (typical 2 in a dual setup, not OE) out of my 77 because of clearance issues when I put the t56 in. the difference in odor is noticeable. I did not notice a significant sound difference that I remember.

I have thought about adding high flow bullet cats right after the collector, if the project $$ is there. One of the rags, maybe GMHT, did an article showing the HP loss from open Y to aftermarket hi flows on an LS2 GTO. Loss of HP was <10. I'm not running for all out hp, I use unleaded street gas, I like clean air, I don't see why not. Maybe flange them on both side to take them out if I want. The cat in my 82 TA was flanged and I would swap it in for inspection. I was a scofflaw teen.

[Later-A-body]

I've owned performance cars for a long time, but I am starting to get tired of the smell and just want to be able to clean up the exhaust without sacrificing too much power. A loss of less than 10 hp is not going to be noticeable in a 500+ hp street car. But will cats be subject to failure if you are running a larger cam with a lot of overlap? I have the ability to tune due to the EFI, so I would think I would be safer than if I was running a carb.

[CamaroAJ]

just remember they need to be as close to the engine as you can or it will take them longer to heat up. that is the reason for A.I.R. pumps on GM, to help light off the cats quicker.

[dipren443]

just remember they need to be as close to the engine as you can or it will take them longer to heat up. that is the reason for A.I.R. pumps on GM, to help light off the cats quicker.


I will be running Random Technology bullet cats on mine when all is said and done. Odor is the main driver. Going to put V-band adapters on the inlet and bolt them right up behind the headers.

[Later-A-body]

CamaroAJ: I agree on the positioning. I will mount them as close to the collector as I can to light them off faster. Spoke with Magnaflow today about cats and what they recommend. Apparently California residents can not buy certain types of converters. They are illegal for installation. I will work around that though.

[CarlC]

Many of the Magnuson "shop" cars have them. Chassis dyno tuning has typically shown a 5-10hp loss on a 500-600hp engine.

I'm looking into fitting them as well. It's really nice to have nearly zero smell.

[1bad68cat]

CamaroAJ: I agree on the positioning. I will mount them as close to the collector as I can to light them off faster. Spoke with Magnaflow today about cats and what they recommend. Apparently California residents can not buy certain types of converters. They are illegal for installation. I will work around that though.

I just bought the metal spun cats manufactured by magnaflow on ebay. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=200445500414&ssPageName=STRK:MEWNX:IT

I believe what magnflow stated is true because Summit/Jegs will not sell the cats I purchased on ebay to california anymore. I bought the cats for the same reason everyone else seems to have them for, smell.

[MrQuick]

You guys running cats, are you experiencing any over heating exhaust issues since I assume most of these fuel systems are not even close to stoichio?

we ran a cat on a race 3rd gen Camaro with carbed 383/big roller cam and it was cherry red half the time.
vince

[86Cutlass383SR]

And people thought I was NUTZ for putting dual cats under my Cutlass instead of leaving them out...

I was running dual cats on the pass side where the stock single cat was. I'm thinking this time around I'll just run a regular duals straight back with a cat on each side.

What is everyone doing about heat shielding on the cars that didn't have stock cats? I know some cats have a heat shield, is that ehough heat shielding or are you running a heat shield on the floor pan?

[dipren443]

You guys running cats, are you experiencing any over heating exhaust issues since I assume most of these fuel systems are not even close to stoichio?

we ran a cat on a race 3rd gen Camaro with carbed 383/big roller cam and it was cherry red half the time.
vince

How rich were you guys running? I could definitely see boosted cars having issue. N/A cars should be around the 12.5-13.0/1 range for A/F. As long as there are no misfiring issues, I would think a cat would have no issue behind that.

[Later-A-body]

Good point on the heat shields. The Magnaflow spun cats dont have them. I have my AFR tuned to run at 14.4 at cruising speed, and progressively adjusts as low as 12.5 under WOT.

[79ZED]

You can use either a two way or three way cat with a carb, but you really have to keep a close tab on the a/f ratio. If your running too rich ( which is often the case with large overlap cams) you run the risk of overheating the converter and destroying it's effectiveness. At worst, you can have the substrate completely destroyed, wich could clog the converter. Too lean will drastically reduce it's effectiveness.

Using cats with efi is really straight forward and I see no reason why they shouldn't be added, especially if you're running closed loop under most driving conditions. Modern aftermarket high flow cats don't pose much, if any, of an exhaust restriction, unlike the old OEM pellet style converters of the late seventies and early eighties.

John

[TnBlkC230WZ]

Why not weld a header flange on it and bolt it straight to the header?

[H2Ogbodies]

Why not run a methanol injection? That will solve your odor issue and add a bit more power as well as keep carbon deposits in check. Also, running it will raise your octane rating slightly as well.

[Randy67]

Since I just recently finished an LT1 swap in my 67 Elky, I am surprised at how clean the exhaust is on the car without cats, compared to the carbed 377 that was there before. I was expecting to have more exhaust odor. EFI has it benefits. The 377 would have killed any cats I put on it in short order. It would make your eyes water and run you out of the garage even with all the doors open. Of course it didn't have anything to do with the crossram and 2 holleys on top, no sir nothing at all.

[John Wright]

I'm thinking about adding cats too.....we'll see.

[badazz81z28]

Resurrecting this old thread....I'm about sick of the exhaust smell too. Who has installed Cats and were they effective with long tube headers? I would also appreciate a recommendation for effective yet not choke off my engine Cat Converters.

Thanks,

[Todd in Vancouver]

Couple of thoughts;

The manufacturers have in the past had Cat. issues where when they come apart the engine can pull Cat. material back into the cylinder thus destroying the engine. *as per the mount them close comment.

There are a number of universal Cats. available if you go to your local exhaust shop if you are looking for an inexpensive option.

I'm not an expert by any means this are just a couple things I've heard in my travels through my automotive career so don't take it as gospel.

[badazz81z28]

I not to concerend about cost (To a point). The Magna Flow spiro wound cats seem to be priced well. I just would like to have a cleaner smelling exhaust.

[DarkoNova]

Couple of thoughts;

The manufacturers have in the past had Cat. issues where when they come apart the engine can pull Cat. material back into the cylinder thus destroying the engine. *as per the mount them close comment.

I'm gonna go ahead and call shenanigans on that.

[Todd in Vancouver]

I'm gonna go ahead and call shenanigans on that.

Nissan Pathfinder to name just one, 3.5L had Cats come apart and get sucked back into the cylinders and caused numerous engine warranties. VW has also had similar problems and I could continue but I think that gets the point across. If you think I'm full of crap try taking a second and google it. BTW, I've spent a good chunk of my career working for different car manufacturers :)

If you still don't want to believe it than fill you boots and I wish you the best of luck. I was just trying to share some of my experiences.

[badazz81z28]

Anyone yet install Cats???

[woody80z28]

I've run Catcos on my EFI engines. They are cheap and flow ok...but I don't think they are legal in CA.

[Quickboat]

I've got a couple of C6 cats that I thought of integrating into my build but I am carbed right now and dont know how long they would last. Would love to be rid of the smell though.
Plus it would be the end of the occasional excursions on leaded race gas...;-)

[CamaroAJ]

I've got a couple of C6 cats that I thought of integrating into my build but I am carbed right now and dont know how long they would last. Would love to be rid of the smell though.
Plus it would be the end of the occasional excursions on leaded race gas...;-)

If you run them and your tuned on the rich side you will burn the cats up rather quickly.

[Quickboat]

If you run them and your tuned on the rich side you will burn the cats up rather quickly.

Is the permeating exhaust smell due to richness or lean condition at idle?

[CamaroAJ]

Rich because of the unburnt fuel.