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The Correct-Sized Headers Will Give You the Best Performance

Jim Smart Aug 16, 2017
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What is it about exhaust scavenging, headers, and systems that leave us in a perpetual fog? Shorty ... medium ... long-tube? Pipe size? What collector type? Which is the better choice for your application and driving style? Header selection depends upon what you want your vehicle to do most of the time. Do you know how much power your engine is going to make and at what rpm range? Cruising or racing ... perhaps both; a daily driver and/or weekend racer?

Header Types

Header selection also depends upon desired noise levels and heat radiation into the cabin. Short-tube headers—also known as “shorties”—run quieter and radiate less heat. A ceramic coating keeps heat where it belongs: inside the header tubes. Shorties are also an improvement over stock cast-iron exhaust manifolds because there isn’t the restriction experienced with iron castings. Shorty headers deliver better low-to-mid-range torque. Medium and long-tube headers allow an engine to make more horsepower at high rpm.

The 4-into-1 is the traditional long-tube header most of us are familiar with—four primary tubes carefully bent and channeled into one collector. The benefit of long-tube headers is the significant decrease in backpressure due to the separation of exhaust gases into their own individual pipes. Their length also prevents the crossflow of exhaust from one cylinder to another. Long-tubes are also the most versatile header type since they can be tuned in different ways via primary diameter, length, secondary (collector) diameter, and shape to account for different horsepower and operating ranges.

Tri-Y long-tube headers, which were conceived on Shelby Mustangs and Cobras in the 1960s, combine a short primary that is paired with another cylinder that is synchronized in the firing order into a 2-into-1 collector that steps to a larger diameter secondary tube. The two secondary tubes are then merged into a final 2-into-1 collector creating an overall length similar to a 4-into-1 design. The traditional tri-Y works well to build more torque from idle to 4,500-5,000 rpm, making them very effective for street use. Autocrossers and road racers also love them for their midrange torque and increased throttle response.

Shorty headers were conceived because late-model emissions systems require catalytic converters and oxygen sensors located in a specific range close to the exhaust ports. They work well with catalytic converters and meet most emission laws.

Mid-length headers are a nice alternative to shorties but without the ground clearance issues of full-length headers. Mid-length headers keep the tubes and collector up above the chassis but allow for longer primary lengths. Not much length is sacrificed in the primary tubes, but the collectors are very short, which does affect their tunability.

We decided to visit PerTronix for a closer look at its complete exhaust line, header design, and chat with Don Lindfors about how to choose the right header and complement it with the right exhaust system. When you consider advances in header and exhaust system design and function you don’t have to look much further than Detroit automakers to see how critical it is to performance and fuel efficiency. We’ve learned from Chevrolet that headers and exhaust systems are an integral part of engine development because both have a direct affect on how the engine performs. PerTronix looks at engines and exhaust systems as a package via tuning and dyno testing to see how both work together. Pipe sizing and routing are everything to performance and efficiency.

A popular misconception is “larger is better” when it comes to pipe sizing beginning at the header flange working your way back to collectors, pipes, and mufflers. Size depends on the kind of driving you will be doing most of the time along with projected horsepower and torque demands. Another important consideration is space and fitment. You may want the largest header tubes and exhaust pipes available. However, if they won’t fit in the space you have, the desire is moot. The darned things are not going to fit.

Once you have the space issue worked out, the next consideration is engine dynamics. Are you seeking horsepower or torque, or both? Road racers want both torque and horsepower. Horsepower for the straightaways and torque for coming out of the turns. Drag racers want raw horsepower coming off the line. Road-going street cruisers want good low-to mid-range torque with the occasional burst of horsepower to spank some upstart at a traffic light. Maybe you’re going to the drags on a Saturday night where you will want horsepower instead of torque. These are all questions to ask before laying down cash for headers and an exhaust system.

To get the correct primary tube diameter right off the header flange, there are formulas for race headers. However, for a street car, Don recommends the following guidelines: 200-325 horsepower look for 1 1/2-inch primaries, 275-425 horsepower use 1 3/4-inches, 400-500 horsepower opt for 1 3/4 to 2 inches, and 500+ horsepower look for 2 inches or greater. Keep in mind, smaller pipes mean more low-to-mid-range torque.

We know performance enthusiasts like real numbers, so try this.
Primary Pipe Area (PPA) = (peak torque rpm ÷ 88,200) × 1 cylinder ci
For example, let’s say we have a 350ci engine with peak torque at 5,000 rpm.
PPA = (5,000 ÷ 88,200) × 43.75 ci
PPA = 2.48

Since header size is most commonly referred to with the diameter of the pipe there’s more math to figure out what the area of a particular primary pipe is. To find the area, we use A=πr² (remembering that r = diameter ÷ 2). To ease your math anxiety here is the area a few header sizes:

Header Size Area
1 1/2 1.77
1 5/8 2.07
1 3/4 2.41
1 7/8 2.76
2 3.14
2 1/8 3.55

So theoretically, our fairly high-winding 350 with a peak torque of 5,000 rpm should run a set of 1 3/4-inch headers. But if your street-oriented 350 makes peak torque at a more typical 4,000 rpm that would drop the PPA to 1.98, so a set of 1 5/8-inch headers would make more sense.

To see what the theoretical peak torque rpm of a certain set of headers is for your particular engine, just rearrange the formula. For this example, we’ll use our theoretical 350ci engine.

Peak torque rpm = (PPA × 88,200) ÷ 1 cylinder ci

Header Size (PPA) Peak rpm
1 5/8 (2.07) 4,175
1 3/4 (2.41) 4,859
1 7/8 (2.76) 5,544

Remember one simple rule when you’re shopping for an exhaust system. Pipe size directly affects power output. Go large—like 3-inches in diameter—and you will gain horsepower but lose torque. Go conservative on the order of 2 1/4 to 2 1/2 inches and you gain torque. Torque comes from velocity and conservative scavenging and the resulting backpressure. Added consideration comes from cam specifications and the effect on backpressure. Be thinking cam, heads, and exhaust system.

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1. There’s a wide variety of cast-iron exhaust manifolds across a broad range of Chevrolet V-8s, including the LS shown. Admittedly, this cast-iron exhaust header is an improvement over the old classic ram’s-horn manifolds of the classic SBC. However, there’s no substitute for tubular PerTronix brand exhaust headers for the LS, small-, and big-block Chevy V-8s. Replacing the stock manifolds with shorty or long-tube headers is going to net both power and fuel efficiency.

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2. PerTronix offers shorty, mid-length, and long-tube headers in their JBA, Doug’s Headers, and Patriot Exhaust brands. You are challenged with choosing the right header for your application and vehicle mission. PerTronix can help. Before you are not only three header types, but collector types as well: sliding (top), ball and socket (middle), and flange (bottom).

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3. If you’re seeking a quick and easy drop-in replacement for stock cast-iron exhaust manifolds, the shorty is your best choice. Patriot shorty headers are designed as a drop-in replacement for the factory manifold depending upon the vehicle you’re working with. If you have a classic Camaro, Nova, or Chevelle with an LS, it becomes a custom exhaust system.

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4. This is an LS in a classic Camaro. Each PerTronix header system is designed to give the maximum amount of ground clearance possible so lowered cars do not drag their collectors over speed bumps. Each system includes high-quality hardware and thorough instructions for a professional, no-leak installation.

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5. The passenger-side Patriot shorty on an LS in a classic Camaro. These three-bolt conventional flanges make installing a custom exhaust system easy. Patriot shorty headers are significantly less restrictive than the stock manifolds and dramatically increase the power and efficiency of an engine. Patriot’s original shorty design is an innovation of the old long-tube header. With durable stainless steel construction, these headers can take a beating.

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6. Choosing the right header isn’t just about length or tube size, but also flanges and collectors. You want a nice thick flange and solid weld beads, which prevent distortion and gasket leaks. You also want a header flange-to-pipe relationship that doesn’t interfere with spark plug and bolt access.

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7. Long-tube headers aren’t for everyone. They perform best when you’re going for horsepower at high rpm. Not everyone will agree on this; however, it has been proven many times on dynos around the world. Long-tube headers are about horsepower.

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8. We’re installing long-tube Doug’s headers from PerTronix. These are large 1 7/8-inch primary tubes, which allow room for expansion for hot gasses on their way out the door. Street engines call for smaller primary tubes, which improves torque.

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9. Doug’s long-tube headers contour down each side of this LS engine to where they don’t interfere with the steering linkage or the frame, making them a perfect fit for a Nova, Camaro, or Chevelle. Doug’s Headers began as a small muffler shop in East Los Angeles, California, in 1958. The company expanded rapidly into a shop that designed and built innovative headers for muscle cars and many of the sport’s top drag racers.

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10. Equal-length Patriot header tubes from PerTronix bring a new dimension to exhaust tuning. Patriot long-tube headers offer big performance gains and high-rpm efficiency thanks to their long-tube design.

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11. These long-tube Doug’s headers wind out away from the engine to clear the clutch cable, yet still inside the steering shaft, managing to clear everything.

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12. This passenger-side header by Doug’s winds down smoothly alongside the LS engine and clears everything. The thing to remember here is primary tube size. You want primary tubes that are the same or larger than your exhaust ports. Too large and you lose torque. Too small and you lose horsepower.

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13. This long-tube slide collector enables you to choose the type of segue you want into the exhaust system.

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14. We like this conventional three-bolt flange collector designed for easy exhaust attachment between a shorty header and the exhaust system.

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15. The ball and socket collector is the most leak-proof of all and is fitted with an O2 sensor bung. This collector style bolts right up to factory catalytic converters and puts the O2 sensor close enough to gas flow for proper operation.

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16. The long-tube slide collector provides you with an easy connection to the collector. It also places the O2 sensor in the main exhaust path. O2 sensor performance can be hit and miss this far out from the primary tubes. This is something you will have to work with via a professional tuner if operation is irregular.

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17. Pipe sizing, both in the header and exhaust system depends upon what you want your engine to do most of the time. The smaller your primary and secondary tubes, the better your low-end torque. The larger the primary and secondary tubes, the better the horsepower. An additional important consideration is space. How much do you have?

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18. Put your exhaust needs in the hands of an experienced professional exhaust shop that has mandrel bending and can weld like no one’s business. You want an exhaust shop that understands old-fashioned craftsmanship.

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19. PerTronix offers an extensive line of pre-bent tubes in both the Patriot and Doug’s brands for your custom exhaust installation.

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20. PerTronix R&D shop did a complete exhaust installation on our Camaro from the Doug’s long-tube headers to the JBA Stainless Steel mufflers. All the pipes clear subframe connectors and chassis mods.

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21. Any time you are building a dual exhaust system, always use a crossover pipe to tie both sides together in the form of an H- or X-pipe.

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22. PerTronix brand long-tube headers from JBA, Doug’s, and Patriot go nice and flush underneath the Camaro, Nova, and Chevelle. There’s less chance of these guys dragging speed bumps or tall anthills.

Photos by Steven Rupp

Sources

PerTronix Performance Products
San Dimas, CA 91773
909-599-5955
pertronix.com

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