Thinking about using catalytic converters

[65 drop top]

I'm thinking about using catalytic converters with my LS3 525 crate engine. I want to use them primarily to cut down on exhaust fumes, and then maybe tone down the exhaust volume a bit. I talked to the tech at Magnaflow today but he didn't sound overly confident with his answers so I thought I'd double check here. These http://www.magnaflow.com/products?partNumber=59959 are what I'm considering using. So my questions are
1. How far away from the header flange (long tube headers) do they need to be mounted?
2. Will I need any type of heat shield?
3. Is there any type of negative side effects or other issues (tuning) from using cats?

[kochevy67]

I would get a quieter muffler before I put cats on a car. Just my .02

[65 drop top]

My main purpose of adding cats is to reduce exhaust smell

[65 drop top]

double post

[CSG]

1. Put the cat as close to the flange as possible.
2. I would try without.
3. As long as you are not forced induction then not that I have seen.

I will run cats on my 69 when I redo the exhaust for the same reason. High quality spun metallic cats hurt performance very little.

[Later-A-body]

I have done exactly the same as you have proposed on my Pontiac LS7 swap. This was planned out from the start of the build. If these are the 3" versions, I am using the same part number. I had stainless 3 bolt flanges welded to each end of the cats, which are bolted directly to the end of the collectors. This will allow the cats to fire off quickly. I also built heat shields that bolt directly to the underside of the transmission crossmember, and they are ceramic coated. The idea was to eliminate the smell, and it does. I had no exhaust odor at all. As far as I remember, each of these cats will handle approximately 450 hp (3" version), so the 600 or so HP I am making is well covered. I would highly recommend the installation. As far as noise, it made the exhaust a little quieter which I like, but it sounds fantastic when you nail it with the Borla mufflers. I do have all this posted on my build starting on page eight.

[ULTM8Z]

I've been running cats on my car for probably close to 15 years now... been so long I forgot who made them (Walker high-flo cats I think). But yeah, same deal... wanted to get rid of the exhaust smell. They do quiet it down a little as well. I have them mounted right after the header flange since they need to get hot to operate correctly.

I don't recall noticing any loss of power because of them. Even if it cost me a couple of hp though, I still think it's worth it. I don't come in the house with my clothes smelling like exhaust anymore.

[65 drop top]

After all of the feedback, I would really like to runs cats. My biggest concern now is fitting the cats into the chassis. Here is a picture of the chassis and the headers I'm going to use. It looks like the crossmember is right where the cats need to be. I don't have the headers yet so once I get them I'll see if I can mount the cats right off of the header flange, I don't think there will be enough room though. Would mounting the cats behind the crossmember work ok, or is that too far from the headers?

[Zspoiler]

Just run twin hyflow cats just before the mufflers if you have he room.

[Larry Callahan]

I have the same desire. While I havn't fired it up yet I have cat's on my Camaro (crate motor) and I will put one on my inline six in the '55. I just don't see any good reason not to. I really hate the smell without them.

[Interceptor5588]

Any chance of fitting Camaro or Corvette manifolds with cats attached? New stuff is pretty free-flowing, doubt you would notice the 20hp loss over headers. Kills the sound a little though.

[Later-A-body]

Wait until you mock up the headers to see what kind of room you have. I had the headers and cats mocked up before we built the crossmember which allowed the design of the crossmember to fit around the cats. You can always modify the CM. The advantage to the cats being near the CM on my car is that I designed heat shields to bolt to the underside of the CM, and above the cats. It gave me a solid mounting area for the shields.

[mitch_04]

I am on a fuel injection group on Facebook and the subject of injector timing comes up occasionally. Once of the benefits of adjusting the injector timing is that it will drastically cut down on the unburnt fuel smell. Not sure who is tuning it but it's worth a conversation with the tuner, or some additional research.

Just another thought...

[Larry Callahan]

I am on a fuel injection group on Facebook and the subject of injector timing comes up occasionally. Once of the benefits of adjusting the injector timing is that it will drastically cut down on the unburnt fuel smell. Not sure who is tuning it but it's worth a conversation with the tuner, or some additional research.

Just another thought...

Oh! Interesting!

[65 drop top]

Wait until you mock up the headers to see what kind of room you have. I had the headers and cats mocked up before we built the crossmember which allowed the design of the crossmember to fit around the cats. You can always modify the CM. The advantage to the cats being near the CM on my car is that I designed heat shields to bolt to the underside of the CM, and above the cats. It gave me a solid mounting area for the shields.
I already have the chassis and the crossmember is already in place. I don't want to modify it, it's a brand new AME chassis. It looks like I'll have to mount the cats behind the crossmember which I'm guessing is 10-12" off the the collector. I'm going to order the headers soon so I'll know more when they come in. I'm trying to decide between stainless or coated stainless. I'm leaning towards the coated stainless because I want a shiny polished look but with out discoloration.

[mean buzzen half dozen]

I would like to run a cat, but I need a performance 4" one.

Anyone know where I can get one of those?

[65 drop top]

I am on a fuel injection group on Facebook and the subject of injector timing comes up occasionally. Once of the benefits of adjusting the injector timing is that it will drastically cut down on the unburnt fuel smell. Not sure who is tuning it but it's worth a conversation with the tuner, or some additional research.

Just another thought...

This is interesting, I'll be doing some research on this. Thanks.