dual exhaust

[rambling_rebel]

getting some progress on my '82 j10 shortbox stepside project. one of the things I was doing was a 6cyl to v8 conversion (ok started, but not finished the conversion yet).

trying to science out the dual exhaust, has anyone done a dual exhaust on this body style? any hints, suggestions, gotcha's, pictures, mufflers placement, pipe routing?

any insight is appreciated (I have ceramic coated free-flows on it, not that that makes a difference I don't think, just sayin')

thanks
rr

[Tinkerjeep]

I have done duals. The frames are the same from 1975 to 1988 on J-trucks so maybe I can give you some pointers. First off you need to think about these things:

What mufflers are you using?

Where do you want to dump the exhaust?

Do you want to move the gas-tank?

Are you running cats?

What diameter pipe?

What length headers - and are they shorties, tri-ys or full length 4 into 1s?

Do you want a cross over? And if so, where?

[Tinkerjeep]

Once you figure the answers to the above questions out, you need to answer this: Are you a welder? And do you have access to a tubing bender?

The better you are at welding, the easier putting dual exhaust on your Jeep will be, because you may have to custom angle-cut/bend/re-weld some of your tubing to route it away from fuel lines, frame rails, drive lines and transfer case/ tranny shifters and E-brake cables.

Example: I had to cut and weld this passenger-side pipe to clear the transfer case due to the Thorley collector being aimed toward the Quadratrac's front output shaft.


And then I had to do the driver-side too. And then to get the whole system parallel and strait, I had to pull them both back off and do another cut/weld. Its time consuming.

If you are not experienced with welding/laying out pipe, or moving the gas-tank and rerouting fuel lines, I'd suggest you pay a shop to do it for you. A dual 2.5" system with a 2-in/2-out muffler will be easiest for the shop, but both pipes will be routed down the passenger-side inside the frame to clear the gas tank. For all the weight, you might as well just go with a single 3" system along the same route - its lighter weight, and sounds great too.

[Carnuck]

Running exhaust down the outside of the frame on both sides makes it equal, but not the free-est flowing.

[rambling_rebel]

my replies in the body of your text. thanks for your help

I have done duals. The frames are the same from 1975 to 1988 on J-trucks so maybe I can give you some pointers. First off you need to think about these things:

What mufflers are you using?
Flo-pro's I believe, i'll have to double check (they have been on my shelf for years - new, never used)

Where do you want to dump the exhaust?
I would prefer to dump the exhaust behind the rear wheel(s), I don't care if both dump on the same side

Do you want to move the gas-tank?
I didn't take this jeep apart, so I am not clear how the gas tank goes in, yet, but I'd rather not if I can help it

Are you running cats?
no

What diameter pipe?
2 1/2 I believe (going from memory here, i'll measure tonight)

What length headers - and are they shorties, tri-ys or full length 4 into 1s?
I'm using the factory style freeflows, and I have 3 sets of them already to use, plus a plethora of different headers, but I prefer the freeflows, they are already ceramic coated

Do you want a cross over? And if so, where?
I actually have access to a brand new NOS factory cross over that I can chop and reroute both duals down the passenger side, at least that's what I eyeballed tonight. The entire body is off the frame so I have a good view of everything

[rambling_rebel]

I have access to a good muffler shop that has a bender. Also my helpers and brother are all excellent welders. I own a nice setup, but would have to relearn how to use it. At this point I am more curious if I am going down the right bunny hole. Already have about $600 in mufflers and pipes and freeflows, but the fellow helping me wants me to stay with a factory single exhaust, but it IS my truck and I think i'll win the discussion

Once you figure the answers to the above questions out, you need to answer this: Are you a welder? And do you have access to a tubing bender?

The better you are at welding, the easier putting dual exhaust on your Jeep will be, because you may have to custom angle-cut/bend/re-weld some of your tubing to route it away from fuel lines, frame rails, drive lines and transfer case/ tranny shifters and E-brake cables.

If you are not experienced with welding/laying out pipe, or moving the gas-tank and rerouting fuel lines, I'd suggest you pay a shop to do it for you. A dual 2.5" system with a 2-in/2-out muffler will be easiest for the shop, but both pipes will be routed down the passenger-side inside the frame to clear the gas tank. For all the weight, you might as well just go with a single 3" system along the same route - its lighter weight, and sounds great too.

[rambling_rebel]

i'll check here if that's allowed, I thought I heard once it wasn't allowed in Ontario, Canada....but I'm trusting an old memory there.
thanks

Running exhaust down the outside of the frame on both sides makes it equal, but not the free-est flowing.

[Jeepguy77]

I've got duals, they run to just after the cab and dump outwards toward the rear tires. It's 2.5" with thrush chambered mufflers and hedman headers. I had factory manifolds when I first got the exhaust. I'll have to get pics when the snow clears a bit.

[Tinkerjeep]

two clarifictions , but really its moot:
1) Mufflers: are these "turbo" style, or bullet/glasspack style?
2) Headers: Jeep never had "factory" headers. I'm assuming you mean they are the same length as the factory cast-iron exhaust manifolds and would bolt to a factory "Y" pipe?

Sounds like your wishes for a dual exhaust set-up is just like most guys that want full-length pipes and duals. I had two dual systems put on one of my trucks, run the exact same way you want. I didn't like the set-up. I moved my custom built 32 gallon gas tank behind the rear axle and modified the exhaust to run one pipe/muffler down the inside of each frame-rail to dump about 18" ahead of the rear axle. this is in a 131" wheelbase 1979 J20 chassis.

The other system I built followed a similar design but had a cross-over about 2 feet ahead of the rear axle (119" wheelbase J-truck) and ran up and over the rear axle and dumped behind the truck. Ther was no under chassis gas-tank on this truck either. This is what id di sound like with full pipes coming out the back and dual 2.5" chambered Summit racing mufflers: http://s152.photobucket.com/user/tin...00110.mp4.html


I'm currently redoing the entire system to make it fit re-built Thorley Tri-Y headers and have a higher cross-over. I haven't gotten the system completed so I don't have an accurate idea of what the exhaust will sound like when finished. But now its louder with no tail pipe section and just dumping out of the mufflers 1-foot in front of the rear axle.

Here's a rough idea of this system as it was first built by me in 2010. It didn't go over the rear axle yet and I had the stock 1972-79 exhaust manifolds. Aside from where the pipes bolted to the manifolds, this crossover was the only pipe-hanger in the system.






Two areas of concern:
1) clearance.
a) around the transfer case;
b) the tranny shift linkage;
c) the e-brake cables;
d) the trapezoidal cross-member behind the cab;
e) both driveshafts;
f) spare tire.

2) crossover.
a) you'll want it removable if you build it up near the tranny/transfer case so you can remove those drivetrain components if needed;
b) you'll want to think really hard about where to route it in order for it to provide the best effect while limiting the heat radiated from it to the transmission - ideally it should be close to the headers, but the one I built is about 3 feet behind the T-case and goes over the rear driveshaft and it is welded in solid. I'll have to post a pic.

Bearing all that in mind, why not just have the exhaust guys build you a system. You already have most of the spendy bits.

[Tinkerjeep]

New version of Crossover.




Mocked up in place. WAY more driveshaft clearance...which wasn't enough before...

[rreed]

Mine, like others I've seen, has stock manifolds w/ true duals, no cats, 2 1/2" pipe, turbo style mufflers.

RH side pretty much routes straight back from the engine, muffler just before the rear axle, pipe "humps" over the rear axle, exits at the right rear quarter at an angle b/t rear tire and bumper.

LH side routes straight back until after the t-case (T-18/D20) then angles 45* to the RH side and joins along the RH pipe. They both run together side by side from behind the t-case to the mufflers (both tack welded together, vertically), then the LH's pipe "humps" over the rear axle and is routed over to the LH rear quarter, matching the RH side b/t tire and bumper.

Neither pipe are anywhere near the stock fuel tank, they route down the RH frame rail. I think there's room to mount the spare underneath if I wanted w/ the way these pipes are route, but I have a bed mount so it's a non-issue.

I plan to run long tube headers one fine day, while I'm at it I'll have installed a 3-hole joint on the LH pipe beside the t-case because right now it's angled JUST behind the t-case - I would have to remove the entire exhaust in one piece to pull the drive train (!!!). Plan and strategize where you might need access w/o exhause pipe in the way. Take the time/money to install a joint or two so you won't have to pull massive sections of exhaust or like mine - the whole darn thing!

[rambling_rebel]

don't know if linking to another forum is allowed here (if its not, delete my post, sorry), but here's a link to a thread on an amc forum showing kind of where I'm at. The only change at this point is the suspension is all tightened down and the engine/trans and transfer case are installed. I was wondering if it would be better if I wait until the body is on before I get too uptight about any of this. I was kind of curious when I was over wrenching on it a bit the other day how the duals would "run" down the sides, especially seeing the transfer case sticking out the way it does.

http://amccars.net/cgi/yabb2/YaBB.pl?num=1305645878/15

thanks again for all your suggestions

rr

[Tinkerjeep]

Here's what is possible if you don't have the bed on and decide to get creative about front to rear weight distribution.






Moving the immense 32 gallon steel fabbed tank allowed me to rebuild the conventionally run duals the muffler shop built. I like the sound but not all the weigh on one side and all the curves and length in the driver-side pipe. So I did this. It sounds quiet. I run Walker turbo mufflers...Thrush is the same part number, and idling, standing 15 feet away you barely hear the truck! When you step on the loud pedal, a bit, you hear the beast bellow. At idle, there is a slight, deep thrumming due to the dissonant exhaust rhythms interfering with each other, and a good crossover is supposed to reduce this significantly. If you are inside a building or car, the thrumming gets annoying after a while. That's why I decided to include one on my green Jeep. But that is running chambered Summit race mufflers...and they are not what you could call quiet. They sound way more mellow and yet burly. better than the dumb kids around here running strait pipes on their trucks. Strait pipes and blown glass packs just sound stupid: CACK CACK CACK CACK! I hate that. The green truck sounds mean but growls, snarls, bellows, and roars...it doesn't CACK!
(I wish it was drivable and had 35" Swampers on it already...)

[Tinkerjeep]

oh, and I did look at your build thread on the AMC forum. Cool. I love that color. I like the step-side beds, I love the gladiator grills. I just don't much care for 1980s trucks...the factory started cutting corners in some areas. But you ar ebuilding yours to tougher it looks like. Good show.

So it looks like you have the stock 1972/3 to 79 cast-iron exhaust manifolds. Do they have the bosses and steps inside the ports for the air injection nozzles? If so, you can grind those steps down flush and get better flow. I did that on my cast-iron manifolds.



I'd still be using them if the stupid donut-gaskets actually worked in the system. My passenger side donut leaked intermittently. Plus there's all the weight. I think the old thorleys I'm now using are a hair lighter, but they flow better and are way cooler!

BTW is that an original R4B?

[Tinkerjeep]

This may be a little off the main path, but a lot of problems people have with dual exhaust is the idea of using headers. Generally dual exhaust is only required for engines that make 300+ hp. and to get good flow, generally long-tube, 4-into-1 headers are best. But a lot of guys hate headers because some have issues with weak materials. Hedmans being a common header manufacturer for FSJ headers. I'll focus on them from experience.

Hedmans had(have?) 1/4" thick head flanges which bent easily and allowed the center two ports to leak after a few months, but usually after the first year or two of doing that they quit bending and you could get a good set of head gaskets to live for years. I'm working on 5+ years, I think, on my latest set.

Another issue is collectors. Hedman used 1/4" thick collector flanges and they bent and frequently allowed leaks at the gasket. Now they offer ball-in-socket collectors on some models (at least FE Fords anyway, haven't looked into New FSJ Hedmans lately) and that helps reduce a moderate source of leaks at the collector.

Another issue is the collector is generally 3" and necks down sharply to 2.25". I changed that with a stepped reducer in place of the stock "funnel" reducer.

Headman reducer...


Stepped reducer...


The rate of reduction is about half as sharp as it was. Some day I may fab reducers that are 8"-10" long and taper from 3" to 2.5" over that whole distance. But I barely (if even) have 300 hp. So its not high on my list. Or I might fab a 3" system. I have two 4' long 3" tubes now...but I also have two 8' long 2.5" tubes, and new Walker turbos to go with them, so I'll probably stick with 2.5" duals.


My dislike with Tri-Ys stems from the only set I had experience with: a set of 1980s era Thorleys. Dad installed them when he owned the Jeep. He used header wrap too. That was a bad idea in wet/cold, Winter weather. It promoted cracks from thermal shock. All those joints, all expanding and contracting when splashed with icy water. It wasn't long before the Thorleys were cracking out at the seams. They were repaired. Then cracked out again and removed. They lasted 10 years. My Hedman 4-into-1s with thinner steel tubing and no wrap have lasted 20 years come July, and haven't cracked out yet.

The other point about Thorleys is the head flanges were separate, so removal and reinstallation on the cylinder-head was a severe pain. You had to bolt the center port-flange loosely to the cylinder head, then pry the front runner forward or back to get that port-flange aligned to start the bolts. Then the rear was the same way.I fixed that issue.

I had a few sets of laser-cut head flanges made a few years ago for AMC V8 headers I want to build (Some day!) I had some bad port dimensions on the first set so I sacrificed them to make additional Thorley head-flange reinforcement.





The third issue I noticed about Thorleys is that the passenger-side collector aims nearly at the front output yoke on my Borg Warner 1339 Quadratrac. These Headers were designed specifically for 1973-1979 FSJs with Q-trac. WTH? Well, I decided not to chop and re-angle the rusty, 30-year old collector. I just built a collector extension out of 2.5" pipe and now it zig-zags like this:



Somebody will bring up Shorties. I've seen a flow test (here I think) that showed Shorties flowed little if any better than free-flowing AMC manifolds (and they may have been ported to remove the air-injection restrictions). But flow tests are not gospel. So if you have em and you make more street power with them than with your free-flowing manifolds, Testify! We want to know.

So, to wrap this up, with a bit of ingenuity (or sheer stupidity?) you can make a stock set of manifolds flow better, or help offset some of the disadvantages that were/are inherent in using headers. Whichever option you ultimately decide...exhaust components designed and built these days are generally better than what was available 30 years ago.