Exhaust Info

Many people decide to modify their stock exhaust on their Bronco IIs. Typically the reason is for either sound or better performance, maybe even both. The sound achieved is subjective, and what sounds good to one person may not sound good to another (eg: import sound versus V8 sports car verses diesel). Performance can be a tricky thing. If done improperly, performance can be hurt or modified in an undesirable way.

The Law:

There are motor vehicle laws governing exhausts, these vary between juristictions, but generally are similar. The laws address noise and typically address a certain degree (in decibels) to be the maximum tolerable noise, with this law there must be some kind of muffler on the vehicle: thus it is illegal not to have a muffler. The laws also address catalytic converters. It is illegal to remove a catalytic converter and not replace it, sometimes you may even be fined and jailed for doing such. Some laws state that only vehicles less than 10 years old need catalytic converters, others suggest that if it came with one at the factory it must always have one. Other laws address where the exhaust exits. Typically the exhaust has to exit away from all passengers (behind the drivers door), and must point horizontal or down. Exhausts tips may not exit in an upward position. Also, it is usually illegal to add any device that makes the exhaust louder (like the tips you often see on imports). Check local laws before modifying your exhaust.

The parts:

The exhaust manifold is the part that bolts to the engine. It is generally large and heavy. The purpose for this is to minimize the noise emitted by the exhaust. Few vehicles came with headers. Headers are basically thin tubes welded to a flange that bolts to the engine. The purpose of a header is to allow better cooling than a manifold, but because headers have less metal to insulate noise, they create a louder exhaust. Headers are also much easier to make than manifolds, since manifolds require casting, where as headers can be produced by welding and bending tubes. A header that is modified correctly can be made to make more power, and can help lower or higher end power band. Headers are commonly avaliable aftermarket in varying degrees of quality.

Collector pipes are associated with headers. It is the pipe that attaches to the end of the header so the header can be mated to the round exhaust pipes. Typically on vehicles with manifolds there will be either just the exhaust tube connected to the manifold, or a Y-pipe style used on some V shaped engines. The Y pipe is designed to connect the exhaust from the left and right manifolds into one single round exhaust pipe. There are many variations of the Y pipe including H shaped pipes. A Y pipe may be used with some headers.

The catalytic converter is a very important part for emission purposes. Essentially a catalytic converter is filled with special metals that react with toxins leaving the engine "catalyzing" with them to create less harmful gasses or liquids. Stock catalytic converters are made of stainless steel and tend to last a long time. If needing a replacement look very carefully. Many aftermarket catalytic converters do NOT flow as well as stock (even some of the cheaper "high flow" ones are actually more restrictive). Also, many aftermarket units are less emission friendly than stock. Stock converters are subject to harsh government testing for quality, longevity, and emission control, aftermarket units are NOT, so choose wisely. A good high end aftermarket unit, however, may be better than stock, but you will pay. Chances are if there is a "high flow" aftermarket unit that costs a lot less than a stock one, it probably isn't worth your money. Additionally, there are several types of converters. I will clasify them in 2 categories though: normal (newer style), and air injection models (older units). Older units required air to be pumped into the convertor via an airpump. The air pump was typically was a pump driven by the accessory pullies (like an air conditioning pump). These old units tend to be very restrictive and get very hot. If your vehicle has one, you will need to find a catalytic converter that has an air inlet, or switch to a newer style unit and get rid of the air pump.

Mufflers tend to be the most discussed part of the exhaust system. There are more mufflers avaliable than any other part of the exhaust system, and the muffler is a crutial controller for the overall sound. Prices range from cheap (about $15 and up to several hundred dollars). Important things to look for are metal material and thickness. Cheap mufflers tend to use a cheap steel or aluminized steel that often rusts out quickly, typically in the thinner units. A very good muffler would be made of stainless steel. Also note the construction: is it pressed together, or welded at the seams? Welding is the better method. Essentially there are 2 types of mufflers: restrictive, and free flowing. Restrictive mufflers tend to have metal inside the muffler in a varied way (tubes, tunnels, channels, etc). Free flowing tend to have little in there. Free flowing tend to be inexpensive, and give a very loud pungent, un-precise noise, a typical example is the glass pack (or cherry bomb) muffler. The restrictive units tend to be more expensive. It is a myth that free glowing makes more sound and power than a restrictive muffler. A good, well tuned restrictive muffler may flow as much, and be about as loud as a free flowing muffler while giving a deeper more throaty tone, but it all depends on the quality. Weather or not a muffler is too restrictive is dependant on many characteristics, but mainly how much the engine flows. If the engine sucks in so much air, the muffler should allow that air to exit fairly easily. On most smaller engines (4 cylinders, v6s, and small block V8s, flow is not an issue as the mufflers tend to be effeceint enough to handle them).

Exhaust tubing. Well you have to connect all the exhaust components together with tubes. If replacing the stock exhaust, the tubes may be purchased pre bent and cut to factory specifications. If making your own custom exhaust you will need to bend and cut the tubes yourself. Many exhaust shops are happy to do this part for you as they have the proper equipment to do it right. But you still have to choose the size and metal to use. For best performance use the same size tube as stock, or NO more than 2 sizes larger. On the Bronco IIs, 1 7/8" 2" or 2 1/4" tends to be best. Quality in pipes depends on the thickness and material used. Thicker tubes last longer, but can be very hard to bend. Stainless steel will last longer than regular steel, but is extremely costly. You also have to consider where the exhaust will be mounted so that the pipes and other components will be out of the way of the trucks moving parts (axles, drive-shafts, springs, etc). And also far away from anything flamable. You also have to consider where to put the exhaust hangers that will mount the exhaust to the frame of the vehicle.

Putting It all Together:

You will need to start with a header or using the stock manifolds. If using a header, there are some products avaliable in the aftermarket. The main things are weather it is 2wd or 4wd. On Bronco IIs there is little room for the drivers side header to exit by the bell housing since the steering linkage, starter, radius arm end, and front driveshaft (on 4wd) are all there. On 4wd vehicles, the driver side exhaust (from the headers collector) will have to be routed under the bell housing to the passanger's side because the front driveshaft would be in the way (on 2wd this is not an issue). Now you decide weather or not to cross the two sides over. I reccomend this. Crossover can be achieved with the stock style Y or H pipe, with an x pipe, a crossover pipe, or simply by running the tubes into one dual input muffler. But before we discuss mufflers we have to mount the oxygen sensor at (or slightly behind) the crossover. The oxygen sensor must be as near the engine as possible since it only operates properly at tempertatures above 600 degrees farenheit; for this reason your crossover should be near the front of the vehicle as well. After the oxygen sensor we can place whichever catalytic converter you chose. Then your choice of muffler and tail pipes. The exhaust may exit the sides or out the back, your choice.

This is a typical stock Bronco II exhaust (some may have a split/dual catalytic converter, and may have a resonator towards the rear axle).

This next set up is probably the best modified version. It is completley legal, best for performance, very good for sound and works with appropriate headers on 2wd and 4wd trucks.

The following is a good dual exhaust that uses the muffler as a crossover. The oxygen sensor is not shown, but in this setup would have to be installed in the header's collector tube. This is legal as well and will work with 2wd and 4wd vehicles.

This next setup is a classic style dual exhaust using an "X" pipe as a crossover. It would typically be used on a muscle car. The mufflers may be placed anywhere in the rear. It does not leave appropriate space for a catalytic converter (which would have to mount towards the transmission). It is not good for 4wd since the exhaust will hang low.

This style will not work on 4wd (because of interference with the front driveshaft), but would be good for 2wd trucks. It is a true dual and with a larger diameter tube could help with high end power. Some low end torque may be lost though. I recomend this for a 2.8 litre with long tube (Heddman headers).

Now you are asking yourself where do I buy Bronco II headers?

 

For the 2.8L

-Hedman Headers p/n 89380 (painted) or 89386 (treated).  2wd only

 

For the 1988-1990 2.9L

-Pacesetter p/n 70-1117 (painted) 72C1117 (coated) for 2wd

-Pacesetter p/n 70-1118 (painted) 72C1118 (coated) for 4wd

-JBA p/n 1632 (chrome) 1632JS (silver ceramic)-auto transmission

-JBA p/n 1632-1 (chrome) 1632-1JS (silver ceramic)-manual transmission

 

For The 86-87 2.9L

-JBA p/n 1630 (chrome) 1630-JS (silver ceramic)

 

Note that the 86 and 87 2.9L uses an EGR tube, and JBA is the only manufacturer that offers a header to support those engines. JBA are the only headers that have threaded oxygen sensor ports. I have not found a manufacturer for 4x4 2.8L headersl; however, you may be able to find a "factory" Ford 2.8L header found on early Aerostar vans with the 2.8L V6. These are short tube headers and should work with a Y-pipe. If you have more questions about the headers, contact the manufacture (they all have websites).



Tech page written and edited by
Ben Hart

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