LD85

I might be adding cats to my 85 in an effort to help control the fuel smell

Is there enough room to put dual cats under the 85? Where did you put them? Which brand has the smallest or does it matter?

I have a Magnaflow hi-flow 85 single cat I have used in the past, I don't know if there is any advantage to going with dual or not.

I have wanted to go to true dual anyway so if there is enough room, I will probably go dual

sailorsteve

Do you mean, raw fuel smell? I don't see how cat(s) will change this, if you have this smell, you have a leak somewhere. If you mean, the exhaust "sweet" smell, that's normal for any car with cats.

GREGGPENN

Dual is better for flow. I called Magnaflow once to get an idea of flow numbers thru bullet vs main cats. The numbers weren't THAT much different. (Though it's safe to assume bullets flow better.) And, though we (in the forum) say cats don't hurt flow that much, I was surprised to learn hiflow cats don't flow any better than say....a performance muffler.

IIRC, 350-450cfm is about what you can expect. Models vary in flow -- as do types. Ceramic is on the lower side while metallic are higher (flow).

Do the math and you'll see one main cat (and, for that matter one central pipe section) restricts flow more than duals. (The short a single pipe section is, the less it restricts btw).

In the case of cats, a single main cat will slow your exhaust flow to less than 500cfm. Probably in the 400's. Duals, OTOH, will still let your exhaust flow up in the 700-900 cfm range. (900 cfm is pretty darn good btw)

With an engine simulator, you can figure out how much each will lower your rwhp. Obviously, a single cat will lower it most.

OTOH, I think a larger surface area main cat will provide more catalyst to convert fumes. If you have the room, two back-to-back bullets might work as well AS one main cat (or max emissions control).

There should be room for either config.

BADDUCK

I am running a single main Magnaflow high flow universal cat and it works great. I removed the two pre cats and kept the main. It cost about $65.

LD85

Thanks for staying on track guys,

I will do some mock ups and see how I can fit two in, and where I can do this.

twin540

As close as you can to the engine, and I would put a heat shield to prevent carpet fire like blackharleyman.. Keep us posted with many pics

LD85

I'm liking GreggPenn's info, i would rather have less performance loss if possible.

My buddy RJ had a 406ci that did 11.5 on street tires and he put the single y-pipe cat on and it lost .5 seconds, we were blown away

The new FAST XFI will tune put most of the valve overlap and the tuner tells me that a cat "might" be necessary to get it the rest of the way gone, if it is even possible.

So I figure I would be better off to get planning on that now.

GP

Kubs

Here is a picture of my homemade y-pipe with high flow bullet style cats:





I have dual 3" pipes on my car.

LD85

kubs, thanks a ton, I had a suspicion that they had to go up around the side of the tranny, looks like you did a nice job of tucking them in to the limited available space

GREGGPENN

BTW...for the general reading public, consider that cats really don't hurt the performance of a stock C4 much. That's because 2.2cfm is what it takes to support 1HP. (IOW, the amount of flow necessary to avoid impeding things.)

Since L98's are in the 220-250hp range, it only takes 500cfm of exhaust flow to cover it's needs.

Notice on the LT (when HP jumped to 300) that they started using dual cats. I don't think this was by accident. It's because you can't get over 600cfm thru one cat. They just don't flow that well.

1991Z07

I used Random Tech. bullet CATs on mine when I converted to a true-dual system.

I used a Corsa LT-based system, bought the stock exhaust hangers from GM and had a shop custom bend the head pipes from the CATs to the "H" pipe on the exhaust system.

I just slipped the Random CATs onto the headers (3" OD on headers, 3" ID on the CAT inlet). They came with a 3" wide stainless band-strap to secure them to the headers.

P/N was 141-30001 on the CATs, and I don't see the strap clamps on there...call and ask them about them. It's the same ones in Kubs 2nd picture though...can't imagine a lot of manufacturers on that item.

P.S. I've got a U-joint rattling, so it needs to go up on the lift this week. I'll take some pics of it and post them.

GREGGPENN

These are what I used with my headers. That's because they run so far back. (They might also come in 3".)

http://www.car-sound.com/02product/d...niversal=54976

These help to turn the corner into the center tunnel.

mseven

LD, my suggestion is definetly using a dual set-up. Once at 400 in. and above you need it to flow. Additonally if buying bullets buy ones with stainless screens instead of ceramic pucks. I originally had RT bullets and they were very good. The tunnel on the 85 I believe has to be very similar. No matter were your choice of installation (foward or rear), there will be additional heat in that area, so you may want to consider some extra inualtion on on the plastic areas near the cats. Here is a pic of the first set-up using bullet cats:

here is how it is now, everything welded no cats and 3" to the rear then necked to 2 3/4":

LD85

beautiful mseven!

Can I but the pipes pre bent or did you have them custom bent?

mseven

thanks...combo of both. They started as RT for L98 all mandrill bent stainless tube. They were then 're-fitted' for aftermarket trans linkage clearance, lt hangers, and entirely welded etc.
A closer look at my budd's welding/modding:


*note the room in the tunnel...(3" bullet cats work, but will need some extra insualtion as to not melt the floor)

twin540

Were did you locate the hangers m seven? Very similar to mine ,but not as nice

1991Z07

He's got factory GM hangers on the back...you can see the springs on them in the photo. They are located at the 3rd member, just inside the camber adjustment bolts.

I'd guess he used the same factory mounts at the trans for the exhaust system. Bolts right onto the trans and holds it up at the front.

I think my hangers ran me $40...

88BlackZ-51

Mick, Larry, Joe etc........

If you talk to Jim he will mention that cats really take power away (sort to speak).

Are you concerned of this at all Larry? Maybe the FAST will hit the tune more spot on, and eliminate a bit of that smell that both of us are not too found of.....

LD85

I am pretty much over caring about loosing 5-10 hp. When I build the next engine, i am going to focus on TQ anyway, I would like to have 5XX RWTQ on the next engine which will do away with the valve overlap and minimize high RPM issue, but obviously it will increase the risk of component breakage!

But if the tune takes it out, then that would be great, $2200 well spent!

88BlackZ-51

What about if its 25-30 hp? Would you care then?

I havent read anything yet that stats how much is lost when dealing with cars like ours in the 500-600chp level.