CATS on the 33?

[mofpa01]

Has anyone tried fitting catalytic converters to their 33? When I had #36, I had asked F5, and they suggested replacing the mufflers with CATS. I ended up just going with a vintage 289, where I would have had to just meet 1967 emissions standards and smog equipment. Toying with the idea of giving the 33 another go, and still think the simplest solution would be to do the vintage engine again, but I'm a big fan of the Coyote. I know it can be done, just would probably have to have a custom exhaust built.

Thoughts/Opinions?

Paul

[TigerBill]

I have an LS3 installed and have been working on exhaust options for the last two weeks. Finally decided. I bought a crate engine package called the E-Rod engine by GM. It is an LS3 with cats and the ECM is program for them and is supposed to be California legal. However, I live in TN, so not that important. The engine comes with the corvette style exhaust manifolds that exit in the center. They send with it camaro style that exit in the rear and instruct you to use those. The catalytic converters are in two stages with oxygen sensor mounts before and after the first stage. Needless to say, all of that would not fit in the '33 frame. The FFR recommended Hooker headers would not work as they hit the starter on the passenger side. I ended up going with the corvette manifold (which meant I had to cut off the camaro flanges on the cats and weld in a corvette flange - thanks Data), then cut the second stage cat off altogether. I know the 2nd Cat is doing something ( not sure if this stage is NOx or organics), but the o2 sensors are before this stage, so it shouldn't affect the ECM control. Then had to cut and weld a couple of the pieces of the ss exhaust to make it match the muffler location without the cat getting too close to the starter, frame, etc. I have rear exhausts, so the side exhaust pipes were extra and the bend in that piece was a pretty good match for what I needed so I cut a piece out of that to make the transition. Then I coated the carbon steel parts with ceramic paint, cured it on my grill (yes, I'm from TN) and installed it. Everything looks ok, but I'm not ready to fire up the engine just yet. Here are a couple of pics to illustrate.

exhaust1.JPGexhaust 2.JPG

[NorthStarUnlimited]

I think I'd go with F5's recommendation to just replace the mufflers with the cats... I think you'll be impressed with the sound.

[Hazelwwp]

I installed the Coyote in my 33HR with the F5 supplied mufflers -- no Cats and no problems (except the stalling problem for which there is now a solution). I visited with forum member KaiRod in Hanau, Germany a couple of weeks ago to see his 33HR. He installed Cats and fabricated a custom rear exhaust but he did not use the Coyote. He built the whole thing himself -- including the body work. He has a really good build page and is very talented. He would be a good source of information for you -- send him a PM.

On another issue, the Coyote has far more power than the 33HR needs. Mine won't hook up -- rear end goes fishy when you get on it. Consider adding a traction control system.

[Tom Veale]

Here are a couple of pics to illustrate.

exhaust 2.JPG

Hi Bill, How do you get those cat converters to float in mid-air like that?


I did a little looking around for cat converters to replace the mufflers. There are several single stage cats available in an "oval" shape. There are different inlet and outlet diameters and several have angled inlets similar to Bill's. Since there's generally a heat rise over the catalyst (exothermic reaction) shielding would be important relative to the mufflers. Some companies sell their cats with a shield attached, some are just bare cats. If I spot some that are close to the FFR mufflers, I'll post part numbers here.

Best regards, Tom

[TigerBill]

Now that I have thought about it some more, I believe I am going to weld up some pipes on my discarded second stage cats so that they have the same connect points as my mufflers so they can be interchangeable and try it both ways for sound and odor. One possible problem with putting an all in one cat in the muffler position is that the inlet temp will be lower, unless you insulate the pipes reall good, and may be too low to get the reaction started. Any info on that. Also if I put my second stage cat at the muffler location, the first cat is ok, but will I also have e low temp problem for the second cat?

[Tom Veale]

Hi Bill, You are right that if one uses a two stage single cat in the current muffler position it will be receiving cooler gasses and be less effective upon startup and for a while thereafter. A good part of the 'magic' of newer cars catalyst converters is that they start to work very quickly so that emissions are very low even on a relatively cold engine.

In using the cats on the '33 in place of mufflers, there may be some noise reduction and the secondary benefit of lowering emissions on a warm engine. It won't be as effective as a modern car, but it should still reach an effective temp after a short while of running.

In your case, the first cat is working to reduce CO and CHx emissions (unburned and partially burned fuel), the second cat is there to reduce NOx, most likely.

Best regards, Tom

[Data]

I've managed to fit the full EROD Cats in with a little creative work at the manifolds using the Corvette manifolds. I'd love to put them where the mufflers are, but that would take away the full emissions qualification of the system. They obviously aren't finished yet, and they're close to a couple of frame pieces, but I think they'll be ok in the end. The bottom of the front cats hang about 3/4" below the frame rails. If you want a different picture/view of how they fit, let me know.

Data

20130612_204252_zps4d927223.jpg20130612_204217_zpsef75eca0.jpg

[Tom Veale]

Hi Data, I ended up dimpling the stainless tubing at the cross-threws at the frame. That gave me extra clearance for expansion, etc.

Best regards, TV

[Hammer-Dan]

TigerBill, you interested in any help? I want to build something but no experience in kit cars? I have basic mechanic skills and do most of my own maintenance. Give me a shout 533-4127 sometime.

[Data]

Well, I guess I have been remiss in updating my build progress. Here are some pictures of the more completed EROD exhaust, with both cats.
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[In33anity]

Started mocking up my exhaust w/ 100 cell low profile racing cats this weekend. Trimmed the frame braces and will put in plate like ridetech. Cats will go on either side of the trans in middle of the tubes shown between the sensor bungs.



Here's an image of the same cats that will be welded in:

[Pro Built]

Great post