Interesting Discovery
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
Interesting Discovery
My '79 L82 is up on high jack stands for the winter as I do a lot of cleaning and (mainly) preventative maintenance.
I've only had it about a year as the spouse presented it to me for a birthday present as a car built the year I turned 16. It was very nicely running, licensed and insured but in need of a lot of work--mainly electrical.
The engine seems completely stock down to the emission controls. I was surprised to find such in my area of the country which has always had quite lax emission control enforcement and requirements. Stock exhaust manifolds and I even verified that the A.I.R. pump is functioning.
Performance always surprised me as being very good for an emission controlled car of that era--it made me wonder why.
Why?
No catalytic converter and true dual exhaust with 2 1/2" (minimum) o.d. pipes all the way back from their connection to the exhaust manifold! I'm almost ashamed to admit that I never noticed it wasn't installed. Needless to say the A.I.R. pump belt is now removed
I've only had it about a year as the spouse presented it to me for a birthday present as a car built the year I turned 16. It was very nicely running, licensed and insured but in need of a lot of work--mainly electrical.
The engine seems completely stock down to the emission controls. I was surprised to find such in my area of the country which has always had quite lax emission control enforcement and requirements. Stock exhaust manifolds and I even verified that the A.I.R. pump is functioning.
Performance always surprised me as being very good for an emission controlled car of that era--it made me wonder why.
Why?
No catalytic converter and true dual exhaust with 2 1/2" (minimum) o.d. pipes all the way back from their connection to the exhaust manifold! I'm almost ashamed to admit that I never noticed it wasn't installed. Needless to say the A.I.R. pump belt is now removed
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
The catalytic converters used on the '79's were very high flowing and didn't reduce the power at all UNLESS they got plugged with carbon because of an oil burning engine. When they fail chunks of their core break out which makes them flow even more.
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
Mike, back in 1977 myself and a couple of friends all bought similarly equipped, new Corvettes. They of course came equipped with the early "pancake" style converters. All of our cars would top out at about 125 within a couple of MPH of each other. A few years later we were all lamenting how much power we were losing as a result of the converters and how we really should do something about it.
One friend decided he would change over to the C3 side pipes offered in '69 and I decided to install a "test-pipe" in place of my converter to see for ourselves what difference it made. With the stock original exhaust manifolds (2" outlets), both of our cars would then hit 130. Not sure how much horsepower that equated to, but it was definitely noticeable.
I don't believe that you would see that much of a gain today with the monolith converters most vehicles come equipped with today however.
Good luck... GUSTO
One friend decided he would change over to the C3 side pipes offered in '69 and I decided to install a "test-pipe" in place of my converter to see for ourselves what difference it made. With the stock original exhaust manifolds (2" outlets), both of our cars would then hit 130. Not sure how much horsepower that equated to, but it was definitely noticeable.
I don't believe that you would see that much of a gain today with the monolith converters most vehicles come equipped with today however.
Good luck... GUSTO
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
These converters were filled with pellets that were not nearly as free flowing as the later monolith's. I recall back the early 80's that by then many of them would "clog" and become restrictive. Typically between about 75k and 100k miles. I believe the Monoliths, sometimes referred to as hi-flowing converters didn't get introduced until about 1981.
Good luck... GUSTO
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
Please explain to this ignoramus why a great many people in the day and until this day insist that "opening" the exhaust will result in significant performance improvement from an engine designed for maximum performance that also complies with government regulations.
Burning Brakes
Joined: Oct 2008
Posts: 1,037
Likes: 14
From: Mobile Alabama
I will explain - the "pan cake" style cat was developed using existing refinery catalyst technology. The platinum loaded alumina sol based spheres were fine as a catalyst, but did not hold up as well in an automotive use. The exhaust flow had to travel through the void space between the beads. It was not the best flowing equipment when new. As beads broke down, the fines would migrate to the voids and cause restriction. The engine controls (tuning) at the time were not near what we have now, and a bad tune could carbon the cat. If leaded gas was used (pretty common in the mid to late seventies), the catalyst was poisoned, and carbon would plug the voids, as would happen with an oil burner. The later "honeycomb" extruded catalysts are much better flowing, and tend to last longer.
Burning Brakes
Joined: Apr 2008
Posts: 1,222
Likes: 93
From: shelbyville West Michigan
no scientific basis whatsoever for what I am about to say, but, I grew up with all GM RWD vehicles. every one I and my friends had, eventually the exhaust rotted off after the cat. we would drive them with just the cat. they were louder, but nowhere near as loud as with no cat. they also had a noticeable seat of the pants power increase.
my feeling was that the muffler restricted the exhaust flow more than the cat did. while the cat did restrict more than just straight pipe, it probably didn't rob any real power, it was the mufflers that did...especially the really quiet ones on stock cutlass/caprice/monte carlo's, etc...
just my observation and recollection from the 70's/80's...taking off the cat but leaving the stock exhaust/mufflers probably did nothing for performance...
my feeling was that the muffler restricted the exhaust flow more than the cat did. while the cat did restrict more than just straight pipe, it probably didn't rob any real power, it was the mufflers that did...especially the really quiet ones on stock cutlass/caprice/monte carlo's, etc...
just my observation and recollection from the 70's/80's...taking off the cat but leaving the stock exhaust/mufflers probably did nothing for performance...
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Race Director
Joined: May 2003
Posts: 10,956
Likes: 409
From: California
Remove the the cat, put on a true duel exhaust with a X-pipe, headers, and some good mufflers like Borla, and you WILL feel the difference from bottom RPM to the top, and it shows in the Dyno very well... .. BEST #1 MOD FOR A C3 CORVETTE...
Burning Brakes
Joined: Jul 2015
Posts: 823
Likes: 57
From: Austin TX
Early '70s factory dual exhaust was very free flowing. It was one of the best you could buy at the time and much superior to glasspacks. If that's what's in this '79, the PO did you a favor. 
Last edited by 454Luvr; Dec 7, 2015 at 06:15 PM. Reason: typo
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
I'm pretty much pleased with the performance as is even if I'm no longer as confident about what is and isn't stock. It does have true dual exhaust but with the stock exhaust manifolds. The mufflers have definitely been replaced and have a great sound. I see "HOG" and "1068" (two different lines) in raised lettering on the top of the mufflers.
Race Director
Joined: May 2003
Posts: 10,956
Likes: 409
From: California
I'm pretty much pleased with the performance as is even if I'm no longer as confident about what is and isn't stock. It does have true dual exhaust but with the stock exhaust manifolds. The mufflers have definitely been replaced and have a great sound. I see "HOG" and "1068" (two different lines) in raised lettering on the top of the mufflers.
If you are running through a single cat, you do NOT have true duel exhaust.
Re-read your first post... Sorry... Sounds like you do not have the Y to the cat... Yes... Made a differance when I first removed mine many years ago also...
Last edited by pauldana; Dec 7, 2015 at 04:49 PM.
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
True duel exhaust does NOT "Y" into catalitic converter and then out... True duel starts from the exhaust manifolds and end in the back... The ONLY linkng between the 2 would be a "H" or "X" pipe..
If you are running through a single cat, you do NOT have true duel exhaust.
Re-read your first post... Sorry... Sounds like you do not have the Y to the cat... Yes... Made a differance when I first removed mine many years ago also...
If you are running through a single cat, you do NOT have true duel exhaust.
Re-read your first post... Sorry... Sounds like you do not have the Y to the cat... Yes... Made a differance when I first removed mine many years ago also...
What threw me off was that the A.I.R. pump was installed, connected and functioning. I verified its' operation. I'd never really looked for the cat as I assumed it had to be there.
Burning Brakes
Joined: Jul 2015
Posts: 823
Likes: 57
From: Austin TX
Sorry if I wasn't clear. My surprise is that there is NO catalytic converter and that I have TRUE dual exhaust from the stock manifolds through to the mufflers.
What threw me off was that the A.I.R. pump was installed, connected and functioning. I verified its' operation. I'd never really looked for the cat as I assumed it had to be there.
What threw me off was that the A.I.R. pump was installed, connected and functioning. I verified its' operation. I'd never really looked for the cat as I assumed it had to be there.
Former Vendor
Joined: Jan 2015
Posts: 412
Likes: 64
I will explain - the "pan cake" style cat was developed using existing refinery catalyst technology. The platinum loaded alumina sol based spheres were fine as a catalyst, but did not hold up as well in an automotive use. The exhaust flow had to travel through the void space between the beads. It was not the best flowing equipment when new. As beads broke down, the fines would migrate to the voids and cause restriction. The engine controls (tuning) at the time were not near what we have now, and a bad tune could carbon the cat. If leaded gas was used (pretty common in the mid to late seventies), the catalyst was poisoned, and carbon would plug the voids, as would happen with an oil burner. The later "honeycomb" extruded catalysts are much better flowing, and tend to last longer.
Drifting
Joined: Apr 2004
Posts: 1,411
Likes: 126
From: Mequon WI
My '79 L82 is up on high jack stands for the winter as I do a lot of cleaning and (mainly) preventative maintenance.
I've only had it about a year as the spouse presented it to me for a birthday present as a car built the year I turned 16. It was very nicely running, licensed and insured but in need of a lot of work--mainly electrical.
The engine seems completely stock down to the emission controls. I was surprised to find such in my area of the country which has always had quite lax emission control enforcement and requirements. Stock exhaust manifolds and I even verified that the A.I.R. pump is functioning.
Performance always surprised me as being very good for an emission controlled car of that era--it made me wonder why.
Why?
No catalytic converter and true dual exhaust with 2 1/2" (minimum) o.d. pipes all the way back from their connection to the exhaust manifold! I'm almost ashamed to admit that I never noticed it wasn't installed. Needless to say the A.I.R. pump belt is now removed
I've only had it about a year as the spouse presented it to me for a birthday present as a car built the year I turned 16. It was very nicely running, licensed and insured but in need of a lot of work--mainly electrical.
The engine seems completely stock down to the emission controls. I was surprised to find such in my area of the country which has always had quite lax emission control enforcement and requirements. Stock exhaust manifolds and I even verified that the A.I.R. pump is functioning.
Performance always surprised me as being very good for an emission controlled car of that era--it made me wonder why.
Why?
No catalytic converter and true dual exhaust with 2 1/2" (minimum) o.d. pipes all the way back from their connection to the exhaust manifold! I'm almost ashamed to admit that I never noticed it wasn't installed. Needless to say the A.I.R. pump belt is now removed
Why remove the AIR Pump?
Thanks
Thread Starter
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
I have not removed the A.I.R. pump, but I did remove the belt that operates it. Why?
A.I.R. stands for "Air Injection Reaction" with that reaction occurring in the catalytic converter. With no catalytic converter there is absolutely zero reason for that pump to be running as there is no place for the required chemical reactions that reduce noxious emissions to occur!
A.I.R. stands for "Air Injection Reaction" with that reaction occurring in the catalytic converter. With no catalytic converter there is absolutely zero reason for that pump to be running as there is no place for the required chemical reactions that reduce noxious emissions to occur!
Melting Slicks
Joined: Feb 2006
Posts: 3,105
Likes: 96
From: Sunrise FL
[QUOTE=SwampeastMike; With no catalytic converter there is absolutely zero reason for that pump to be running as there is no place for the required chemical reactions that reduce noxious emissions to occur![/QUOTE]
Not exactly true, some pre cat cars have AIR pumps also. Some further combustion does take place in the exhaust piping.
I would save EVERYTHING you take off the car for posterity.
BTW, if you look up the special components of the L82 you will be pleased!
Not exactly true, some pre cat cars have AIR pumps also. Some further combustion does take place in the exhaust piping.
I would save EVERYTHING you take off the car for posterity.
BTW, if you look up the special components of the L82 you will be pleased!
Burning Brakes
Joined: Jul 2015
Posts: 823
Likes: 57
From: Austin TX
I have not removed the A.I.R. pump, but I did remove the belt that operates it. Why?
A.I.R. stands for "Air Injection Reaction" with that reaction occurring in the catalytic converter. With no catalytic converter there is absolutely zero reason for that pump to be running as there is no place for the required chemical reactions that reduce noxious emissions to occur!
A.I.R. stands for "Air Injection Reaction" with that reaction occurring in the catalytic converter. With no catalytic converter there is absolutely zero reason for that pump to be running as there is no place for the required chemical reactions that reduce noxious emissions to occur!
Last edited by 454Luvr; Dec 8, 2015 at 09:31 PM.