I recently bought a ’76 F-250 4x4 with a 390 out of a muscle car (it has relatively high compression and a hot cam). The exhaust system is pretty rusty and I plan on replacing it. What about purchasing headers versus using the stock iron manifolds? I’ve talked to several people about headers, and have heard of problems with them leaking and constantly having to replace the gaskets. If I buy a set of headers, will they have problems with leaking and/or their durability when four wheeling? If I do choose the headers, would a dual three-inch exhaust system be too big for the engine?
Headers are a benefit to any engine, especially one with high compression and a camshaft change. Every off-road vehicle I have ever owned has had headers and so have most of my street drivers. However, like anything, you get what you pay for. When it comes to headers, price is pretty much what determines the quality of the product, as defined by thicker flanges, heavier wall tubing, and quality welds. The thick flanges will ensure that they maintain a flat contact area with the cylinder head, which in turn helps to ensure that the gaskets don’t leak.
After the headers are installed, you will have to go back several times and retighten the bolts. The heat cycles will cause the bolts to loosen up as the gasket slightly compresses. It’s not a bad idea to just double check their tightness every time you change the oil as part of your maintenance program.
While I have successfully used the fiber gaskets over the years, there are some soft copper gaskets available from Summit Racing (www.summitracing.com) that are said to hold up better. If you’re really worried about the bolts coming loose, Stage 8 Locking Fasteners (www.stage8.com) has some special bolts that have a locking tab that prevents the bolt from turning once installed, but can be easily removed.
Generally speaking, the paint used by most header manufacturers is more of a protective coating intended to keep them from rusting while in storage than it is a long term coating. On mild steel headers I bead blast them, wipe them down with lacquer thinner and then paint them with VHT (www.vhtpaint.com) FlameProof Coating. I have tried other high-temperature paints but have found VHT to be the best brand. Some headers can be had with a special coating such as Jet Hot (www.jet-hot.com) that offers superior protection to paint. The best (and most expensive), however, is to go with stainless steel, as there is no need to paint or plate and they last almost forever.
As for the tailpipes to complete the rest of the exhaust system, 3 inches is overkill, and besides being hard to route, will be expensive. A 2½-inch dual exhaust system with smooth, wrinkle-free bends should be more than adequate when combined with some quality mufflers.
Diesel Engine Stoppers
Exactly how does an exhaust brake work? I understand the theory, but also know that if you stuff a potato in the exhaust pipe the engine will stall. Also, are Jake Brakes and exhaust brakes synonymous?
Tiido and Anni Tennelo
No, Jake Brakes (www.jacobsvehiclesystems.com) and exhaust brakes are not the same thing. Let’s go over the Jacobs, or Jake Brake, first. A Jake Brake modifies the timing on the exhaust valves so that, when braking is desired, the exhaust valves open slightly right as the piston reaches the top of the compression stroke, or near top dead center (where ignition normally occurs in a gas motor). When on the upstroke, the piston compresses the air in the cylinder to 1⁄18 its original volume, assuming the compression ratio is 18:1. This creates a lot of drag on the engine. The Jake Brake then releases the compressed air, and the energy stored in it, before it can push back on the piston during the downstroke. In addition, releasing the compression prevents any fuel in the cylinder from igniting. Remember, diesels don’t have spark plugs, they rely on the heat from compression alone to ignite the fuel (except during cold starting when glow plugs are utilized). So, you’ve got drag on the upstroke and no power on the downstroke.
A man by the name Clessie Cummins (Yes, the same one who developed the engine) developed the compression-release engine brake in 1954 and sold the idea to the Jacobs Manufacturing Company, which started production of it. It soon became part of trucking lore.
There are styles of Jake Brakes that are quiet. There are also other companies that make compression-release engine brakes, not just Jacobs. Jake Brake gets a bad rap because the name not only seems to have become generic to exhaust engine brakes, but also has become a sort of icon. The noise is caused by the escaping air and it is possible to muffle it to become almost inaudible, but for some reason some truckers seem to like the noise, even if the public doesn’t.
The exhaust brake, meanwhile, is nothing more than a butterfly valve in the exhaust system. When activated, this valve restricts the exhaust gas flow and increase back-pressure in the engine. There are several ways to control the valve, and different manufacturers have used electronically controlled solenoids, electric motors, air cylinders, and even vacuum motors driven by a vacuum pump. When the exhaust pressure exceeds a set amount, the valve is designed to open, thus preventing damage to the engine or that part of the exhaust system in front of the valve. Yes, if the valve stayed completely closed for any length of time, I suppose the engine would stall out. However, there is some leakage, and some systems even have a separate bypass valve.
The biggest advantage is excellent compression braking on downgrades under heavy loads. I have one made by B-D Power (www.B-Dpower.com) on my own Chevy Duramax diesel 3500 truck and very seldom do I have to use my brakes on even the steepest downhill grade, even with a load that may exceed the truck’s maximum CGVW. Having owned an exhaust brake, I doubt that I would ever be without one. Another benefit is faster cold weather warm-ups.
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