HRR Tech Editor Mike Mavrigian answers some common questions that builders have about choosing and installing an exhaust system.

What Size Header Tube Diameter Should I Get?

A common mistake that many novice builders make is to purchase a set of exhaust headers that feature large primary pipe diameters, thinking that bigger is better. For the street, just the opposite is true. Even if the engine features an overbore, nutty cam and forced induction, unless you plan to operate the engine at wide-open-throttle at all times, smaller- diameter tubes will provide more usable low- and mid-range torque.

Just like any other engine-related component, you need to consider the application and how the vehicle will be driven, and then choose accordingly.

Pipes that are too big in diameter will move more exhaust volume, but the gasses will move more slowly. Smaller-diameter pipes will move less volume, but will scavenge the gasses quicker and at a higher velocity, and that’s what you want for street driving in the 1,500–3,500- or 4,000-rpm range. Headers, as opposed to cast iron exhaust manifolds, increase exhaust gas speed (velocity), which not only increases gas scavenge but also reduces heat build-up, which in turn reduces the chance of pre-ignition. Smaller tubes scavenge faster.

For the sake of clarifying exhaust terms, primary tubes refer to the exhaust tubes that directly channel exhaust from the cylinder heads (the headers). Secondary tubes include the tubing that routes gasses from the header collector rearward.

A general rule of thumb is as follows: For street operation, a typical small-block engine should be fitted with 11⁄2–15⁄8-inch primary tubes. A big-block engine would require 13⁄4–17⁄8-inch tubes. Once you get up into the 5,500-rpm range and higher, larger diameter tubes would be of benefit, but, realistically, how often will you operate at that engine speed? Choose your primary tube diameter based on the vehicle’s most-common operating range.

Kit 82300 from Hedman is available uncoated or with Hedman's HTC Coating.

Should I Use Shorty or Long-Tube Headers?

Theoretically, longer-tube headers (where primary tubes extend for a longer distance before joining the collector) will produce slightly more horsepower. However, that scenario is more applicable to racing. For a street vehicle that’s outfitted with secondary pipes and mufflers, you probably won’t see or feel any difference between short and long headers.

It’s certainly no secret that shorties are popular (block huggers are often favorites), and sometimes necessary in terms of fitment and clearance issues. Don’t feel that you’ve short-changed yourself by opting for block huggers. In terms of power for the street, it’s really not a big concern.

Do I Need a Coating for My Headers?

There are three reasons to consider a coating for exhaust headers: to prevent surface rust, to enhance appearance and to increase performance. Painting the headers with high-heat paint is certainly a less-expensive option, but taking advantage of a ceramic coating may make more sense.

The ceramic coating, which serves as a thermal barrier, reduces radiated heat and forces the exhaust heat to run through the system, as opposed to being lost to the surrounding air. This has an obvious side benefit of decreasing radiated heat in the engine bay, reducing the chance of fuel boil, and minimizing heat-related damage to rubber components, under-hood paint, starters, etc.

If you planning to have a turbo setup, the thermal barrier coating will also make the turbo exhaust more efficient.

Avoid using a heat-barrier wrap on street exhaust systems. While these heat-barrier fabric wraps are excellent at containing heat and protecting surrounding surfaces, moisture can be trapped between the wrap and the tubes, and can lead to long-term rust or corrosion. Heat wraps are great for race systems, but are a no-no for street-driven applications.

Today’s thermal barrier exhaust coatings are available in a variety of colors and finishes, depending on the supplier. You also have a choice of purchasing headers that are already coated, or purchasing bare headers and sending them out to a coating specialist.

Hooker offers these long-tube headers for LS engines that are in 1955-1957 Chevys. They come in a ceramic finish.

A word of caution about coated or painted headers: If you have a fresh engine that has not yet been fired (for example, if you’re planning to run the engine on an engine dyno), it’s best to use a set of spare headers for the initial run/break-in. If the engine isn’t set up just right, it may be too lean during initial running, which can elevate exhaust temperatures and can cause severe cosmetic damage to the paint or coating.

If you don’t have the luxury of having a spare set, check with your engine dyno shop. Chances are good that they’ll have headers in their dyno room that will serve during break-in (many dyno shops will want to gather exhaust gas temperature anyway and will have headers fitted with sensors). If all else fails, one option is to purchase a set of bare headers and use them for initial firing/break-in/dyno run. After the engine has been sorted, then send the headers out for coating.

Should I Use an H-Pipe or X-Pipe System?

An H-pipe is a lateral pipe that connects the left exhaust bank to the right exhaust bank. An X-pipe is, well, an “X” pipe intersection that crisscrosses the two exhaust paths. The basic purpose of either design is to create a balance between the exhaust pulses, which, in theory, should provide additional power in terms of low- and mid-range torque. Will you notice the difference at typical cruising speed on the street? Maybe. There are too many other variables to consider, such as cam profile, cylinder head design, etc.

One advantage of using a crossover system relates to the exhaust sound. A crossover (H or X) should provide a deeper tone and should reduce or eliminate “back rap,” assuming you prefer avoiding this. Personally I enjoy the sound of a rappy exhaust as the throttle is eased off.

Which is better—an H-pipe or an X-pipe? For the street, you probably won’t see a difference. In race applications, certain X-pipe designs have been found to provide better throttle response, but generally only after extensive dyno and track testing while tuning the other engine variables.

In theory, an X-pipe should provide a smoother “communication” between the two exhaust banks and will likely provide a smoother sound pitch. However, for the street, if you decide to tie the two banks together in an effort to balance the exhaust pulses, either design is acceptable. The choice may be dictated by available space in terms of fit and clearance.

Is There An Easy Way to Seal the Area Between the Cylinder Head & Header Flanges?

Sealing the mating area between the cylinder head and the header flange can sometimes present a challenge. If everything works as it should, in theory you should have no leaks. However, in the real world, the exhaust header flange may not seat perfectly (especially in the case of individual-pipe flanges), or certain bolts may be difficult to access, resulting in under- or over-tightening.

To help avoid leaks, make sure that all threaded holes in the cylinder head are clean and free of burrs. Apply a thin smear of anti-seize or moly lube to the bolt threads, especially if using stainless steel fasteners, and try to obtain the correct torque values. If you do run into an annoying exhaust leak, you might try a thin bead of Ultra Copper RTV from Permatex on each side of the flange gasket. I’ve had great success with this over the years.

After the engine has been run and heat-cycled a few times, and the engine has completely cooled, go back and re-tighten all header flange fasteners. It’s a good idea to check torque at least once or twice each season.

What Diameter of Exhaust Pipe do I Need?

As far as the remainder of the exhaust system is concerned (from collectors back), we again need to consider pipe diameter from a performance standpoint. Even though big pipes may look cool, those with too-large a diameter can slow exhaust scavenging. For the sake of appearance, you can always install oversized exit tips for rear or side exit systems in order to gain that “big pipe” look.

For more on exhaust systems and components, check out the September issue of Hotrod & Restoration.

Tags: Cylinder Heads, Engine Building, Exhaust Systems & Components, Headers, Mike Mavrigian, Permatex, Tech Tips, Thermal Management