Exhaust single to dual on a tight budget - Then we get into some after issues

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,567
Reaction score
10,735
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
I still need to do the shields and yes I know I still need to take pictures which I will do tomorrow. The low resonation I was complaining about is gone with the tailpipes installed and generally the exhaust note is more mild, which is what I expected. At idle you cannot hear the exhaust at all, at cruise of light throttle it's there but not loud. Even with the hammer down, and getting up there in RPM, I hear that classic V-8 sound but at a volume you could talk over. I could tow the trailer over the pass with this exhaust and not get sick of listing to the exhaust. So we'll see how I feel about it over the next few weeks, but I think this is just fine. When I get the cats on it in a couple weeks it's mellow the tone even a little more.
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,567
Reaction score
10,735
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
All you picture ****** here ya go. Since the story and the info here is completely useless maybe these will be useful....

Below, here are the exits!

You must be registered for see images attach
You must be registered for see images attach


The Thrush turbos. That band clamp was just temp, and I can take that off whenever.
You must be registered for see images attach


Below right side muffler and tail pipe to pump and hose clearance, as you can see nothing touches but it sure is close. I'll be doing shields and wraps to prevent long term heat exposure issues.
You must be registered for see images attach
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,567
Reaction score
10,735
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach


Plan is to weld all the joints together after I'm happy with the setup, so that would be after the cats are on and I'm 100% sure I'm keeping these mufflers, which in reality I'm quite sure I will do.
 
Last edited:

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,567
Reaction score
10,735
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
Ok now I have another issue I'd like to make improvements on and I just know @Ricko1966 will have some good ideas on this.

So he doesn't have to read the entire thread, the short version is I went from a single exhaust with a catalytic converter to a dual exhaust system without cats. Sometime in the first few weeks on December I'll get cats back on the truck, I got to get past the 1st when I get paid.

So I no longer have a working exhaust gas analyzer, but my nose tells me that Nitrates of Oxide (NOx) is very high. Obviously the old cat was doing quite a bit to clean that up and that's great, but I figure if I can reduce the NOx it'll probably make the new cats last longer, and also make my time between now and then more pleasant.

So she's a stock 305, that the PO put an edelbrock 1706, which basically 1406 with an adjustable secondary air flap. Timing is set to the factory spec I think 4BTDC.

Air pump is intact and functional.

So I need to check that my EGR valve is still functioning, though I know the EGR isn't working at idle if it lowers the cylinder temps, less NOx is created so the cylinder temps would be likely to remain lower at idle and make the idle smell better.

I will also try to turn the idle mixture screws a tad richer to see if that helps out a little.

I know timing plays a big part in NOx production and being lean will get NOx levels up. So Rick anything I missed or any ideas?

Again this wasn't an issue when the cat was on and cats will go back on, so even if I'm not able to make improvements the cats should clean it up. I just want to improve it if I can.
 

Radiohead

Reducing tire diameter 1000 revolutions at once
Joined
Mar 17, 2022
Posts
1,687
Reaction score
5,568
Location
Low Earth Orbit
First Name
Eric
Truck Year
MCMLXXIX
Truck Model
C-20 Silverado Camper Special
Engine Size
454 crazy cubes, or 7.4 luscious litres
The dump bed sure came in handy on picture day. Made it easy to see, lol. Thanks for the visual Rob. Pictures must be a hold over from the ancient Playboy/Penthouse days in our collective youth.

Coil assist plus leaf springs? Interesting. Have you given any thought to air bags in back?

My hangup over putting cats back on is fuel control. Which has me considering one of those Holley Sniper efi setups, so I don't melt the honeycombs. Or maybe a tbi system off an '87. Or a yet undiscovered solution. I was an emissions inspector in Colorado back through the 80's so I am not opposed to cleaning up my exhaust, unlike some certain people whose mothers never taught them not to shyt in their own beds.

Thoughts?
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,567
Reaction score
10,735
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
The dump bed sure came in handy on picture day. Made it easy to see, lol. Thanks for the visual Rob. Pictures must be a hold over from the ancient Playboy/Penthouse days in our collective youth.

Coil assist plus leaf springs? Interesting. Have you given any thought to air bags in back?

My hangup over putting cats back on is fuel control. Which has me considering one of those Holley Sniper efi setups, so I don't melt the honeycombs. Or maybe a tbi system off an '87. Or a yet undiscovered solution. I was an emissions inspector in Colorado back through the 80's so I am not opposed to cleaning up my exhaust, unlike some certain people whose mothers never taught them not to shyt in their own beds.

Thoughts?
Well I'll tell ya, the cat I took off looks pretty decent inside. With a well tuned carb a cat should last for years and years, it won't last as long as it would on an EFI car though. A lot of vehicles in the late 70's though the early 90's came carb & cat equipped from the factory, and todays honey comb cats are light years ahead of the pellet cats, both in terms of function and longevity.

EFI will never go on my truck, for one thing it's a lot of cost for not much gain in my opinion. And I've had some terribly battles getting aftermarket system to work decently on customer vehicles to know I'd never want one. So I'd take a factory EFI vehicle for sure, but not interested an aftermarket system for me, other folks seem to have great luck with them. I will say towing the trailer and running up long grades wide open I've gotten the cat hot enough to smell the heat, but no damage was done and it continued working just fine.

Yes, those are aftermarket overload coils. It's only a 6 leaf 3/4 ton truck so the coil overloads really help out both with keeping the rear end up and with stability when towing. There are a number of different weight compacities for those coils, and IDK what I bought without looking at my paperwork but it's one of the lighter ones I just wanted a bit of a boost, it's not like I carry camper all the time. Again air bags are out of my budget. I've done air shocks on trucks I've had in the past, but I like the rock solid reliability of the coils with no concern of air leaking.

Ya, the dump bed gets used a lot. It's even helpful for getting heavy stuff in the bed just by tilting it a bit, and after I got the exhaust done to the mufflers the rest I did on the ground just by reaching down to it with the bed up. Make diff services super easy too.
 
Last edited:

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,567
Reaction score
10,735
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
Update on the NOx thing. I richened the idle mixture up 1/4 turn, and drove it at lunch. No noticeable change. Then I remembered that I had switched the vacuum advance from ported to manifold, and that retarding timing will lower NOx usually. So I changed the vacuum source back to ported. Seemed to make a major difference, way, way, way less nose detectable NOx at idle. So I've got to drive it for about 2 hours tonight some of that will be in traffic and we will see how that goes. I may lean it back out to where it was before or go in the middle but first I want to see that the problem is gone.
 
Last edited:

ChuckN

Full Access Member
Joined
Nov 8, 2022
Posts
825
Reaction score
2,308
Location
Bellinham, WA
First Name
Chad
Truck Year
1981
Truck Model
C10
Engine Size
350
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach


Plan is to weld all the joints together after I'm happy with the setup, so that would be after the cats are on and I'm 100% sure I'm keeping these mufflers, which in reality I'm quite sure I will do.
Looks great! Nice job.
 

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
3,681
Reaction score
5,212
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
Robyn sorry man,not much we can do we are stuck with our fuel and air supply,so tune,correct mixture and egr is all you can do. To make it worse too lean is worse than too rich for nox but visaversa for milage. So tune for best mpg and get your cats,or don't. My problem isn't people running no emissions for practice reasons,they bought a car already butchered,or ? and it's not 8n the budget,what gets to me is all the monkey see monkey do emissions deletes for no reason at all and no benefit for doing it.
 
Last edited:

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,567
Reaction score
10,735
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
Robyn sorry man,not much we can do we are stuck with our fuel and air supply,so tune,correct mixture and egr os all you can do. To make it worse too lean is worse tan too rich for nox but visaversa for m8lage
Oh I know an emissions era 305 is going to be what it is and I know it, I just know this was way worse than a normal 305 missing the cat. I really think that moving the timing back to ported made a difference. We will see when I drive it tonight. I really liked the way it idled on manifold vacuum, but it is what it is I'll trade that off for less idle stink or longer cat life any day of the week. Of course this means I have to readjust the idle speed and the fast idle speed but, and further fine tune the mixture, oh well I guess.
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,567
Reaction score
10,735
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
Well sir cleaning up idle emissions is ported vacuums primary if not its only function.
That's my understanding. I do prefer the idle feel of manifold, but as you and I talk about these 305's were pretty much built to run with their emissions equipment, so I guess it makes sense. Sadly I liked the idle quality of manifold but that's ok.

So the drive home was better, but I traded NOx for just mild stink. I might fool around with leaning it out some, but I think in the end it'll just be a bit smelly until I get the cats back on.

AND hopefully getting the cats up to operating temp won't be an issue, since I'll be going from one cat to two, but I think with the air pump and all it'll be fine.
 

Radiohead

Reducing tire diameter 1000 revolutions at once
Joined
Mar 17, 2022
Posts
1,687
Reaction score
5,568
Location
Low Earth Orbit
First Name
Eric
Truck Year
MCMLXXIX
Truck Model
C-20 Silverado Camper Special
Engine Size
454 crazy cubes, or 7.4 luscious litres
Rob, where does the output of the air pump go on your system? Pre or post cat? The original stuff piped it into the cast iron manifolds IIRC. It does on my '79. Didnt you go to tube headers? I forget
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,567
Reaction score
10,735
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
Rob, where does the output of the air pump go on your system? Pre or post cat? The original stuff piped it into the cast iron manifolds IIRC. It does on my '79. Didnt you go to tube headers? I forget
I'm running stock manifolds, and yes the air pump, pumps into the manifolds. Why do you ask?

To be honest at this very moment I'm a little pissed at myself for not waiting until I had $$ for the cats and just do it all at once, what with all the complications with the dual setup, I should have just spent the extra dollars and rebuilt the single setup.
 
Last edited:

Latest posts

Forum statistics

Threads
41,428
Posts
894,256
Members
32,880
Latest member
csmill83
Top