Headers vs Downpipe pre-76 exhaust smell
Thread Starter
Instructor
Joined: Mar 2019
Posts: 125
Likes: 12
From: Richmond, VA
Headers vs Downpipe pre-76 exhaust smell
So... Considering just the Cat-less downpipe since not looking to tune due to extended GM Warranty. I've read folks state they didn't want that non-Cat stink; but there's 2 cats (stock) in the mid-pipe, so ?
Besides, headers remove the main, upstream cats anyway.
Is there a difference ?
Besides, headers remove the main, upstream cats anyway.
Is there a difference ?
Le Mans Master
Joined: Oct 2014
Posts: 8,674
Likes: 2,728
From: Atlanta GA
Don't remove the cats , you might regret it . I would go the route Kracka went with the AFE high flow cats and the catless x pipe
As far as headers , you have the option for cats and they are located in the mid pipe , yes you can remove the cats but ....
I can't speak for the folks that say they can't smell the car without cats ..... but I can speak for my self . Sitting at a light with the windows open and the wind blowing the wrong way .....or that first start in the morning in the garage ...is terrible
Dave
As far as headers , you have the option for cats and they are located in the mid pipe , yes you can remove the cats but ....
I can't speak for the folks that say they can't smell the car without cats ..... but I can speak for my self . Sitting at a light with the windows open and the wind blowing the wrong way .....or that first start in the morning in the garage ...is terrible
Dave
Thread Starter
Instructor
Joined: Mar 2019
Posts: 125
Likes: 12
From: Richmond, VA
Interesting, it seems the main cats (upper) do more then the mid-pipes. I've always thought the opposite. I still don't understand why its different then headers; they do the same, remove the upper cats ?
Le Mans Master
Joined: Oct 2014
Posts: 8,674
Likes: 2,728
From: Atlanta GA
The oem pup cats only exist to help with COLD start emissions when the main cats are not hot enough to handle it all . That is the reason why the main cats are located as close to the exhaust ports as possible so they heat up fast
When you go with headers and high flow cats you still will get some smell because the cats are farther downstream and take longer to heat up but once hot ... you won't smell anything . Every time I started my C6 in the garage my wife would comment on how bad it smelled .... I am about to do the same with my C7 ... cant wait to hear her complaints again
Dave
Last edited by Dcasole; Jun 9, 2019 at 10:10 AM.
Thread Starter
Instructor
Joined: Mar 2019
Posts: 125
Likes: 12
From: Richmond, VA
No they don't do the same ... because headers move the "main cats" down stream into the mid pipe . The density of material in the main cats is much more than the secondary "PUP" cats
The oem pup cats only exist to help with COLD start emissions when the main cats are not hot enough to handle it all . That is the reason why the main cats are located as close to the exhaust ports as possible so they heat up fast
When you go with headers and high flow cats you still will get some smell because the cats are farther downstream and take longer to heat up but once hot ... you won't smell anything . Every time I started my C6 in the garage my wife would comment on how bad it smelled .... I am about to do the same with my C7 ... cant wait to hear her complaints again
Dave
The oem pup cats only exist to help with COLD start emissions when the main cats are not hot enough to handle it all . That is the reason why the main cats are located as close to the exhaust ports as possible so they heat up fast
When you go with headers and high flow cats you still will get some smell because the cats are farther downstream and take longer to heat up but once hot ... you won't smell anything . Every time I started my C6 in the garage my wife would comment on how bad it smelled .... I am about to do the same with my C7 ... cant wait to hear her complaints again
Dave
Last edited by RobsCountach`; Jun 9, 2019 at 10:19 AM.
Race Director
Joined: Jan 2014
Posts: 10,709
Likes: 7,102
From: Fulshear, TX
Check out my review thread here: https://www.corvetteforum.com/forums...cat-pipes.html
Keeps the cats right where they should be for emissions, warranty, and stock tune reasons.
Keeps the cats right where they should be for emissions, warranty, and stock tune reasons.
Last edited by Kracka; Jun 9, 2019 at 10:22 AM.
Le Mans Master
Joined: Oct 2014
Posts: 8,674
Likes: 2,728
From: Atlanta GA
I appreciate the input. Yeah, I did know about the PUP cats job; however, I'm still confused at why there is a difference between headers and the downpipe; Unless, of course, aftermarket mid-pipe cats are more filtering then the stock ? Both 'move' the main cats downstream, or do they ?
The best if both worlds , a hi flow cat , no smell , and no need to tune ....
But if I am going thru all this work to install these down pipes and we can argue the validity about if they void warranty , for a mininual power gain .... .....then I am going all the way and installing headers and a tune to get the full power gain ...just my two cents
Dave
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
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
Burning Brakes
Joined: May 2018
Posts: 1,070
Likes: 175
From: Wendell NC
St. Jude Donor '19
I went with Kooks headers/mid-pipe with high flow main and rear cat delete and stock axle back for now. Cold start in the garage can get pretty strong but other than that the smell is minimum at least from my experience.
Melting Slicks
Joined: Aug 2014
Posts: 2,746
Likes: 916
Same here except I went with the Kooks green cats. No tune, no CEL, and the exhaust odor can be described as your experience. No desire to go catless for me...
Burning Brakes
Joined: May 2018
Posts: 1,070
Likes: 175
From: Wendell NC
St. Jude Donor '19
Race Director
Joined: Jan 2014
Posts: 10,709
Likes: 7,102
From: Fulshear, TX
I went for a nice drive today to get some good logs for my tuner and can confirm no strange smells, nothing stronger than stock odor, with these AFE high-flow cat pipes. Garage cold start, cold idle, driving windows up and down, gas station, then hot idle in the garage.
Melting Slicks
Joined: Aug 2014
Posts: 2,746
Likes: 916
Did the AFE high-flow cat pipes make the car louder? Are you still running the stock midpipe?
Race Director
Joined: Jan 2014
Posts: 10,709
Likes: 7,102
From: Fulshear, TX
Yes to slightly louder. It's the most obvious at a cold start or heavy acceleration. Minimal change during regular driving or cruising down the highway in Tour. V4 Eco mode sounds about the same too which is nice because I use it a lot on roadtrips.
Last edited by Kracka; Jun 9, 2019 at 03:10 PM.
Thread Starter
Instructor
Joined: Mar 2019
Posts: 125
Likes: 12
From: Richmond, VA
Ugh. I'm not explaining myself well. So Sorry.
I realize they don't 'move' the cat; it was a reference to your post, assuming a virtual move of the main cat downstream ? When you install headrers you ARE running Cat delete, same as the cat-less downpipe. Both options discard the main cats; There's only the mid-pipe cats that remain.
You can not run headers and say you've got all your cats; you don't as you've deleted the 2 main (uppers).
I'm curious why headers don't smell, that retain the mid-pipe cat and the cat-less downpipe may smell, that also reatains the mid-pipe cat.
Both systems are the same; headers and downpipe have NO main cats; they both just have the mid-pipe cats.
I realize they don't 'move' the cat; it was a reference to your post, assuming a virtual move of the main cat downstream ? When you install headrers you ARE running Cat delete, same as the cat-less downpipe. Both options discard the main cats; There's only the mid-pipe cats that remain.
You can not run headers and say you've got all your cats; you don't as you've deleted the 2 main (uppers).
I'm curious why headers don't smell, that retain the mid-pipe cat and the cat-less downpipe may smell, that also reatains the mid-pipe cat.
Both systems are the same; headers and downpipe have NO main cats; they both just have the mid-pipe cats.
Melting Slicks
Joined: Aug 2014
Posts: 2,746
Likes: 916
The cats that are/can be purchased with header systems are replacements for the main cats and would be considered the main cats. Yes, they are pushed a little further back from the location of where the factory main cats would be, but they are still considered the main cats. It's the smaller downstream (pup) cats that go away with the catless mid-pipe that come with most of the header kits.
Thread Starter
Instructor
Joined: Mar 2019
Posts: 125
Likes: 12
From: Richmond, VA
The cats that are/can be purchased with header systems are replacements for the main cats and would be considered the main cats. Yes, they are pushed a little further back from the location of where the factory main cats would be, but they are still considered the main cats. It's the smaller downstream (pup) cats that go away with the catless mid-pipe that come with most of the header kits.
Melting Slicks
Joined: Aug 2014
Posts: 2,746
Likes: 916
More info here: https://performancebusinessmedia.com...ic-converters/
