catalytic single or dual
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
catalytic single or dual
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
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
Last edited by LD85; Jan 10, 2012 at 09:57 AM.
Drifting
Joined: Jun 2010
Posts: 1,853
Likes: 8
From: Westerly RI
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.
Last edited by sailorsteve; Jan 10, 2012 at 12:06 PM.
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
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.
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.
Last edited by GREGGPENN; Jan 10, 2012 at 07:13 PM. Reason: Changed and to AS. Then added the max emissions phrase.
Le Mans Master
Joined: Jun 2006
Posts: 5,642
Likes: 5
From: One day you're a Comet...the next day you're dust... Arkansas
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.
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
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
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
Le Mans Master
Joined: Oct 2007
Posts: 9,700
Likes: 3,469
From: Akron Ohio
2025 Corvette of the Year Finalist - Modified
2024 C5 of the Year Winner - Modified
2023 C5 of the Year Finalist - Modified
2022 C5 of the Year Finalist - Modified
St. Jude Donor '09-'10-'11
Here is a picture of my homemade y-pipe with high flow bullet style cats:
I have dual 3" pipes on my car.
I have dual 3" pipes on my car.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
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
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
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.
Safety Car
Joined: Feb 2000
Posts: 4,564
Likes: 110
From: Austin Texas
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.
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.
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
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.
http://www.car-sound.com/02product/d...niversal=54976
These help to turn the corner into the center tunnel.
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
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":
here is how it is now, everything welded no cats and 3" to the rear then necked to 2 3/4":
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
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)
Last edited by mseven; Jan 11, 2012 at 08:01 AM.
Safety Car
Joined: Feb 2000
Posts: 4,564
Likes: 110
From: Austin Texas
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...
Race Director
Joined: May 2003
Posts: 10,749
Likes: 41
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.....
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.....
Last edited by 88BlackZ-51; Jan 11, 2012 at 04:41 PM.
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
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.....
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.....
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!
Race Director
Joined: May 2003
Posts: 10,749
Likes: 41
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!
But if the tune takes it out, then that would be great, $2200 well spent!
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.