I am not really thinking of doing any exhaust work on my Bronco at the moment, but eventually I would like to put in a 351 with perhaps 100 HP more than stock. When I have the money, and if I need a motor (I do not currently need a motor) I should not for a long time since has 130K and has been impeccably over-maintained since new; I have all of the service records and it runs and sounds like brand new. But I am planning of keeping this Bronco for a long time and maybe forever.

Anyway, I would want to get the exhaust ready for this. I would probably be keeping the stock exhaust manifolds, at least until the engine is out, I would probably add headers when the new motor goes in as it would be easier. .

What is needed for true duals? One or two catalytic converters? Do they make high-flow catalytic converters? Then there are the mufflers. I would like a nioe sound but not too loud, at least from inside the cab. I would like a nice, subdued rumble, I would probably use a mild cam. I definitely want that awesome V8 growl when you hit the gas though. Some mufflers that I considered were Thrush, Hush Thrush, Flowmaster, Dynamax, and the good ol' Cherry Bomb for that old-school sound. Right now I have a single Dynamax and it is very quiet, like stock. I have had past experiences with Hush Thrush on a 71 Roadrunner 383 and they had a nice, subdued rumble that screamed when I got on it; and I had dual Dynamax on a 99 Dodge Ram pickup with a 318 - they were not true duals and the motor was stock, but Dynamax and duals sounded sweet when I got on the gas. Perhaps would I get enough muffling action if I just had the two high flow cats and the pipes?

I do not want expensive bling bling giant chrome tips. They looked great on my Ram truck, but they don't seem appropriate for my Bronco, and they are also pricey. I would keep the stock location, turned out behind the wheel, and add another one on the driver's side.

I would also probably put a K&N intake in as well, but I do prefer the sealed factory one becuase of water issues. However the new motor and exhaust would probably necessitate on open intake filter, and they do sound sweet in conjunction with the exhaust.

 

To have true duals you have one exhaust pipe running independantly from each other on either side of the truck. No y-pipe, no nothing. An h-pipe is optional to "equalize" the sound, but doing a search in the exhaust forum will shouw you that it is debatable. Do you need cats? Yes. Two. Again, optional. If you always run them to keep emissions down, use the high flow ones. If you dont care, dont bother spending the money. Muffler? Your choice. Flowmaster would probably be the ticket based on your post. I would probably say you would be well off with two 2.5 inch tubes. Two 3 inchers would be too much. I dont wanna get on the "backpressure" debate here. Two 2.5 inchers is just my suggestion.

Hope this helped at all.

-Matt

 

My single flowmaster has a nice subdued sound 'til you get on it. When I got my flo put on, the bum at the place said true duals wouldn't fit b/c not enough room under there, y/n? Also, if you want quiet do the manifolds, the other day the motor was really quiet and I thought the truck had shut off. One of them 'I love this truck' moments. With my headers I have now, I cruise at sixty and listen to my tires, which is quiet cause I got street tire radial things. -Bill

 

A slightly different take on the answers already given.

I agree, true duals do not require a cross-over ("H") pipe however, with our trucks' EEC-IV computer it is REQUIRED equipment. The O2 sensor MUST get readings from BOTH banks of cylinders in order for the PCM to correctly adjust fuel-air mixtures and so forth. No cross-over pipe means no place to put the O2 sensor to get an accurate reading from BOTH banks of cylinders. So the cross-over or "H" pipe is not optional.

You don't necessarily need TWO catalytic converters PROVIDED you can find a cat that has dual input and output ports. Early 90's E-series 3/4 and 1 ton vans had cats and mufflers with dual IN and OUT on them. Removing an operational catalytic converter is a federal offense even if the state you live in has no emissions inspections. If you have to deal with inspections, removing the cats just cause more headaches than its worth.

 

I know about having a pipe run from each header, that's not really what I meant. I was asking about what components work the best ie. the cats, the mufflers, the H pipe. Your answer about the cats confused me though, it seems backwards. Why would I use high flow cats if I always run them for emissions? I am required to have cats because my truck came with them, but I would like the least restrictive cats if I am going to punch up the exhaust.

As far as the tubing size, the smaller the better as far as I am concerned, for issues of space and ground clearance. I don't care about having two giant pipes sticking out of my truck. 2 1/2 sounds fine.

That's also interesting about the cat with dual inlet/outlets. But it seems like it would be hard to get both pipes over to one cat with the limited space under the truck. I have seen 4X4's with custom exhausts that hang way down from the frame and I don't want that. Also one cat should be cheapere than 2, I like that.

 

Considering the lack of space under the Bronco to begin with, routing BOTH pipes side-by-side along the same path as the OEM exhaust may be the best way to keep things out of the way. I mean, if you consider that the 3" Bassani system runs in the stock location and its nearly twice the diameter of the OEM exhaust, it would seem to make sense that squeezing two 2" pipes along side each other may be the best routing method since the left side of the undercarriage is full of obstructions like the T-case and front drive shaft. Not to mention that the fuel ines run up the left side of the frame as well. I wouldn't be too keen on the idea of having an exhaust pipe right below my fuel line.

BTW, at this point in time, I am not aware of anyone actually manufacturing a true dual setup for the Bronco. Any true dual system would have to be a custom job.

 

Agreed. Im a carb guy. I forgot that he's fuel injected. Yes. You need a crossover pipe.

Im also aware of your opinion on catalytic converters. Again, if he is of the same mind as you, get them, put them on. The high-flow ones now-adays filter well, and let the air through well at a good price to keep you legal. However, some people have mechanics that dont care, or just dont want to put them on (their perogative) and thats a whole other argument.

 

You pretty much answered you own question there. The high-flow cats out now filter the hydrocarbons as well if not better than the OEM ones did. You CAN put them on for emissions AND have a free flowing exhaust as well. If high flow cats didnt filter anything they would be useless and no one would be buying them. BTW, these cats are going for under $100 for many applications, so they are very affordable. The dealership would most likely want more for the crappy OEM unit.

-Matt

 

Now that I think about it, true duals can both exit on the same side, behind the tire. They don't necessarily have to come out on either side. That might make running them easier, especially with a dual in/out cat. Perhaps two pipes with a crossover going into the dual cat and exiting out the passenger side behind the tire, with no muffler? I would only be worried that it would be too loud. I want a subdued rumble, not a loud anooying truck. It's still a Bronco, not a hot rod.

 

Your right. They dont HAVE to run on either side of the truck, but for a true dual, both exhaust bank of the engine run independant piping. The theory is that there is less flow interference, thus better performance. I wanted to do this because I didnt want any pipes running under the engine/tranny so I could get at the oil pan easier. I decided instead to run a single 3 inch exhast from manifolds back with a flowmaster y pipe. Just for cost saving of course....

-Matt

 

the purpose of true duals is to have as strait of an exhaust as possible for best flow. so by routing all to one side this will creat alot more bends and turns to run 2 sets of pipes. I would suggest just have a shop build you a custom Y pipe, hiflow cat and flowmaster but run 3" pipe. it will perform better then the duals will .

now for a cam go with 35-255-5 its speed density friendly, look into getting your stock heads ported and polished and maybe upgrade to the edelbrock efi truck intake this will get you close to 100hp/trq if not more.

 

Not sure how running the two pipes side by side would add more bends to the pipes. I mean, yeah the stock setup does a couple of wiggles over the rear axle but otherwise its a fairly straight shot out til you get past the rear wheel. I guess if you think about it, the left side pipe would have one extra bend in it since it would have to come across to the right side. Imagine for a moment that that silly collector (where the O2 sensor mounts) in the OEM Y-pipe didn't bring the two pipes into one. Both would then run the exact same route as the OEM setup and the O2 sensor section would become the cross-over pipe.

I am a proponent of the 2.5-3" single setup myself. But if I was to undertake the project, I think for the sake of having a pattern (to form custom pipes from) and a route to follow, I'd at least look into the idea of running along the OEM path with two pipes.

 

I am not sure about the theory of having the pipes go straight all the way, but if they were run side by side and out one side, they would be mostly straight. I don't want to run them straight out the back because of fumes getting in if the rear window is down and I am driving. As it is, you have to crack one of the front windows to run with the stock exhaust and not fill the truck with exhaust.

 

When I say straight, I dont mean you HAVE to go all the way. What I was trying to say was that it is said that if your pipes have more twists and bends to them, the farther the exhaust has to travel, and the more it is slowed. Also, when running 2 pipes together the drivers side exhaust will be longer than the passenger side exhaust because it has farther to travel. The theory is that true duals (pipes running on each side of the truck) have few bends (pretty much straight until the rear axle) so there is less interference blah blah blah. No one said you couldnt 45 degree them behind the rear wheels.

-Matt

 

I hear you. I don't think that the side-by-side idea would result in any more bends than if one ran down each side. That would be up to whoever is installing the pipes, we could put it up on a lift and figure out the best way. It's true that in the side-by-side configuration, one of the pipes would be a little bit longer. I don't know how much of a real-world effect that would have in a Bronco with maybe 300 HP or so.