Dual exhaust for 4wd '87 V10

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.

Craig S

Junior Member
Joined
Jun 2, 2017
Posts
13
Reaction score
0
Location
Stamford, CT
First Name
Craig
Truck Year
1987
Truck Model
V10
Engine Size
5.7 350
I have just rebuilt the engine in my 1987 V10 5.7 liter 350 1/2 ton 4wd and Im looking for a manifold-back dual exhaust system. My truck no longer has to be emission tested so I dont have to use a catalytic converter and I already have a pair of Flowmaster mufflers, so I need to find 2 1/4" system that fits my truck. Also Im not sure whats involved in reprogramming the computer to make full use of the upgrades I have installed. Does anyone have any suggestions?
 

1987 GMC Jimmy

Automobile Hoarder
Joined
Jan 23, 2016
Posts
5,848
Reaction score
2,387
Location
Mississippi
First Name
Jesse
Truck Year
1987
Truck Model
V1500 Jimmy
Engine Size
350
I have just rebuilt the engine in my 1987 V10 5.7 liter 350 1/2 ton 4wd and Im looking for a manifold-back dual exhaust system. My truck no longer has to be emission tested so I dont have to use a catalytic converter and I already have a pair of Flowmaster mufflers, so I need to find 2 1/4" system that fits my truck. Also Im not sure whats involved in reprogramming the computer to make full use of the upgrades I have installed. Does anyone have any suggestions?
If you installed headers, it'd behoove of you to go with a heated oxygen sensor, but that doesn't require messing with the ECM. You said you're keeping the manifolds, though. If it were me, I'd ditch the manifolds, liberate the power that they restrict, and work my next exhaust system from the collectors back instead of keeping the manifolds. What upgrades have you done that would warrant a PROM reburn? The catless exhaust won't affect anything, and the mufflers won't, either. Did you beef up the engine any in your rebuild?
 

4WDKC

Full Access Member
Joined
Jan 27, 2016
Posts
2,366
Reaction score
1,090
Location
Southern Florida
First Name
Kacy
Truck Year
1987
Truck Model
V10
Engine Size
350
I have just rebuilt the engine in my 1987 V10 5.7 liter 350 1/2 ton 4wd and Im looking for a manifold-back dual exhaust system. My truck no longer has to be emission tested so I dont have to use a catalytic converter and I already have a pair of Flowmaster mufflers, so I need to find 2 1/4" system that fits my truck. Also Im not sure whats involved in reprogramming the computer to make full use of the upgrades I have installed. Does anyone have any suggestions?

I think flowmaster makes a 2.5" system for our trucks, my truck has whats left of a 2.5" true dual system and am thinking about going back to a 2-1-2 setup as i have read a single exhaust promotes better low end torque. i am thinking 2.5" from manifolds/shortie headers to 3 single pipe past tcase, the split to two 2.5s mufflers and tail pipes.
 

smoothandlow84

I'd rather be draggin' frame
Joined
Jan 4, 2015
Posts
2,121
Reaction score
784
Location
Arizona
First Name
Steve
Truck Year
1984 Frame...87 motor and 700r trans
Truck Model
1500 r10 pavement scraper
Engine Size
350 TBI
Dia did the same....ditched all of my emissions including the cats. I ended up installing long tube headers and dual 40 series flowmasters. Tailpipes dump on either side of the truck in front of the rear tires.

I would suggest just going to a reputable muffler shop rather than tinkering around trying to locate a bolt on kit. First of all, the kits if available tend to be more expensive than a custom setup for what you end up buying. Second, with a custom bent setup, you have more options as to where the exits are AND the duals will line up better. Most of the time bolt on kits fit like crap. If you have even the slightest variation of frame, axle or spare tire variance, you tend to have clearance issues.

my true dual piping with tight custom bends installed WITH the flowmasters and the proper hanger mounts was under $400 installed. That also included the old system being removed. Oh yeah...and the work has a full installation warranty that covers broken hangers and leaks.

One more item...depending on your taste and sound tolerability, a single flowmaster dual piped (two pipes out past muffler) will be much louder than dual mufflers into dual pipes. I wanted to tone down the drone so I ended up having a series 50 flowmaster tacked up to duals....way louder than two flowmaster 40 series into dual exits. Just for kicks the shop tacked in a single 10 series flowmaster. Extremely loud and it threw flames

As far as the heated o2 sensor. I installed one and it didn't make any difference. No codes before or after the heated was installed, no ecm changes, no changes in how it runs, idles etc. Im calling b.s. on that theory. It was basically a waste of $40 for the sensor and 2 hours of my time to wire it....and YES it was wired correctly and verified to be functional.....still absolutely no difference with it installed.
 
Last edited:

smoothandlow84

I'd rather be draggin' frame
Joined
Jan 4, 2015
Posts
2,121
Reaction score
784
Location
Arizona
First Name
Steve
Truck Year
1984 Frame...87 motor and 700r trans
Truck Model
1500 r10 pavement scraper
Engine Size
350 TBI
If you installed headers, it'd behoove of you to go with a heated oxygen sensor, but that doesn't require messing with the ECM. You said you're keeping the manifolds, though. If it were me, I'd ditch the manifolds, liberate the power that they restrict, and work my next exhaust system from the collectors back instead of keeping the manifolds. What upgrades have you done that would warrant a PROM reburn? The catless exhaust won't affect anything, and the mufflers won't, either. Did you beef up the engine any in your rebuild?
A catless exhaust will improve driveability. The cats are quite restrictive...especially with age (if they are oem) and time. Removing the cats and restrictive mufflers improves backpressure restriction.
Adding a heater o2 sensor won't make any difference. I had a heated o2 installed...absolutely no difference....none.
 

4WDKC

Full Access Member
Joined
Jan 27, 2016
Posts
2,366
Reaction score
1,090
Location
Southern Florida
First Name
Kacy
Truck Year
1987
Truck Model
V10
Engine Size
350
A catless exhaust will improve driveability. The cats are quite restrictive...especially with age (if they are oem) and time. Removing the cats and restrictive mufflers improves backpressure restriction.
Adding a heater o2 sensor won't make any difference. I had a heated o2 installed...absolutely no difference....none.

ti depends on your setup, a friend installed LT headers and didnt swap the 02 he only had a problem on the interstate becasue of the 2.4X-2.73:1 gears and overdrive would allow the O2 to cool off and set the light while driving 70mph, if he drove at 80 the O2 stayed warm and no light.
 

Craig S

Junior Member
Joined
Jun 2, 2017
Posts
13
Reaction score
0
Location
Stamford, CT
First Name
Craig
Truck Year
1987
Truck Model
V10
Engine Size
5.7 350
First off thanks for the input guys. 4WDKC Im sticking with the manifolds for now just because of a lack of money, down the line I intend to install performance headers. Right now there is no exhaust system at all, the previous one was so badly rusted that it wasnt salvageable at all, so Im looking for a system that I will only have to make adjustments to the intermediate pipes to fit the new headers I get later on. As far as the engine I replaced all the gaskets from the valvetrain up and purchased a cold air intake that I will be installing after the engine is back in the truck. I read somewhere that since Im doing away with emission systems that I dont need to re-install the air pump, is that true? This is the first time I have ever tried to do performance upgrades and Im finding alot of conflicting information so any suggestions would be grately appreciated. Thanks again
 

1987 GMC Jimmy

Automobile Hoarder
Joined
Jan 23, 2016
Posts
5,848
Reaction score
2,387
Location
Mississippi
First Name
Jesse
Truck Year
1987
Truck Model
V1500 Jimmy
Engine Size
350
A catless exhaust will improve driveability. The cats are quite restrictive...especially with age (if they are oem) and time. Removing the cats and restrictive mufflers improves backpressure restriction.
Adding a heater o2 sensor won't make any difference. I had a heated o2 installed...absolutely no difference....none.
A catless exhaust will improve driveability. The cats are quite restrictive...especially with age (if they are oem) and time. Removing the cats and restrictive mufflers improves backpressure restriction.
Adding a heater o2 sensor won't make any difference. I had a heated o2 installed...absolutely no difference....none.
I hear you. My understanding of it is the whole timing of achieving closed loop. I agree that there's no way a one wire sensor on a system that uses headers could set off a Code 13, 44, or 45. It'd be cool to get four TBI 350s (one with stock exhaust, one catless with manifolds, one catless with headers, and one with headers and a cat) together with nominally operating cooling systems on live data scan tools to see when they all switch to closed loop. It sounds redundant, but it covers every variable. I'm not trying to contradict you in the least. In fact, I prefer your way. I don't want to propagate something that's unnecessary, and if the need for a heated sensor is just conjecture, that's just making people buy something they don't need.
 

1987 GMC Jimmy

Automobile Hoarder
Joined
Jan 23, 2016
Posts
5,848
Reaction score
2,387
Location
Mississippi
First Name
Jesse
Truck Year
1987
Truck Model
V1500 Jimmy
Engine Size
350
First off thanks for the input guys. 4WDKC Im sticking with the manifolds for now just because of a lack of money, down the line I intend to install performance headers. Right now there is no exhaust system at all, the previous one was so badly rusted that it wasnt salvageable at all, so Im looking for a system that I will only have to make adjustments to the intermediate pipes to fit the new headers I get later on. As far as the engine I replaced all the gaskets from the valvetrain up and purchased a cold air intake that I will be installing after the engine is back in the truck. I read somewhere that since Im doing away with emission systems that I dont need to re-install the air pump, is that true? This is the first time I have ever tried to do performance upgrades and Im finding alot of conflicting information so any suggestions would be grately appreciated. Thanks again
Yeah, you can get rid of the pump, diverter, and associated vacuum lines. You do need to plug the holes in the manifolds, and I'm not sure what size plug you need. Someone was exploring that same predicament not too long ago, and I think they found what they needed so it's definitely out there. I would also suggest keeping the pump and diverter in a box somewhere. One of our CA guys may need that stuff on a rescue or restore to make it emissions legal, and you may end up being his/her hero.
 

glockholiday

Full Access Member
Joined
Jan 23, 2016
Posts
173
Reaction score
21
Location
Arizona
First Name
Jeff
Truck Year
1988
Truck Model
V10 Suburban 1/2 ton 4x4
Engine Size
350
Now that I think about it my Suburban has the rear fuel tank and this might interfere with saddle tanks on a pickup.
 

75gmck25

Full Access Member
Joined
Oct 13, 2016
Posts
2,017
Reaction score
1,808
Location
Northern Virginia
First Name
Bruce
Truck Year
1975
Truck Model
K25 Camper Special TH350 NP203
Engine Size
5.7
The path of the dual pipes on my '75 GMC K25 does not get in the way of the fuel tanks. They are outside the frame and the pipes are inside. However, if you still have the spare mounted, its best to have tailpipes that flare out to the side and keep them away from the spare tire.

The one issue you may have is that most trucks had single exhaust standard, and with a 4WD and offset transfer case that usually means less clearance on one side of the truck. My transfer case cross member has a dip down on the left side so that there is more clearance than the right. They managed to fit the right pipe up and over the cross member, but it took a couple of bends to get it routed. I have 2" pipes, but I don't think 2 1/4' would be any problem to fit.

I have been told that since dual exhaust was a factory option, there are transfer case cross members that dip down on both sides for exhaust clearance, but I've never seen one.

You can also run pipes under the transfer case ross member, but they are much more subject to damage if you high-center the truck.

Bruce
 

4WDKC

Full Access Member
Joined
Jan 27, 2016
Posts
2,366
Reaction score
1,090
Location
Southern Florida
First Name
Kacy
Truck Year
1987
Truck Model
V10
Engine Size
350

Latest posts

Forum statistics

Threads
41,848
Posts
903,416
Members
33,362
Latest member
Dhatch84
Top