If your vehicle is powered by a naturally-aspirated engine, you already know how important it is to optimize everything so you can make as much horsepower as possible. The right set of headers is a huge part of ensuring your engine is as efficient as possible.
Headers help evacuate exhaust gases from a cylinder through negative pressure. While that sounds simple, a lot goes into the design of a set of headers. The primary tubes need to be able to generate the right amount of velocity to remove exhaust gasses in a controlled and timely fashion. The length and diameter of the header tubes are dictated by the size of the engine, how much air it needs to move, and other factors.
Project Number Cruncher’s 427 cubic inch LS engine that was built by the students at SAM Tech required a good set of headers to reach its full potential since the Dart Pro1 LS 12-degree 285CC CNC heads can move plenty of air. SAM Tech had an idea of how much power the engine could make and where it would make that power, so they decided a set of headers with 2-inch primaries and a 3 ½-inch collector would work best.
We reached out to Louie Filippides and the team at American Racing Headers (ARH) to have a set of headers built that would work with our combination. You may think a custom set of headers would be required for a build like this, but you’d be wrong.
“A custom set of headers would only be necessary on an application that can’t be satisfied by our current catalog. Cars with altered K-members or engines that have been moved back for better weight distribution are some examples of when you would need to build custom headers. It’s unfortunate, but ultimately because of cost, custom headers are usually built out of necessity, rather than the pursuit of more horsepower. People will almost always use an off-the-shelf header if it will save them money. Off the shelf headers will work great if they’re sized properly for the given application,” Filippides says.
Primary tube size and collector size are two of the key measurements for a set of headers. The primary tube size controls the exhaust flow, so you don’t want it to be a chokepoint for the exhaust gases. There are several factors that need to be considered before you select what size primary tubes and collectors your headers need.
“Some factors that we always take into consideration when spec’ing out a set of headers are engine size, overall vehicle weight, converter stall speed, maximum engine RPM, where the RPM drops on the shift, horsepower, and torque. Using that information, combined with our experience in header theory, we can recommend a primary and collector size that will ultimately get you where you’d need to be for that specific application. In most instances when we use that information it will help the end user’s engine net better overall results on the dyno and at the racetrack,” Filippides explains.
The material you select for your headers is important in a naturally-aspirated application. In the past, mild steel was one of the main choices for headers, but most header companies have moved away from it since it doesn’t have good longevity. These days, most high-performance headers you’ll see on a naturally-aspirated engine will be made of either stainless steel or titanium.
The big advantage that titanium brings to the table is its weight — it’s a light material, but that advantage has some strings attached to it. Titanium isn’t as strong as stainless steel, so it’s more likely to fail or crack over time without the correct reinforcements being added to the headers. Stainless steel isn’t as fragile as titanium, but you’ll pay for that strength with its additional weight.
Filippides explains why ARH decided to skip the titanium diet for our headers and used stainless steel instead.
“Material cost is a major factor when dealing with titanium as it’s a much pricier option. When an engine is solidly mounted in the engine bay and it wheelies a lot that can cause damage to a set of headers. An aggressive camshaft and spinning an engine to extreme RPM levels can cause headers to crack. That’s why we use 304 stainless as our material of choice here at ARH. Yes, it’s a slightly heavier material, but it’s also one that retains heat very well, and has the structural integrity to withstand the abuse our customers will surely throw at it year after year.”
If your specific application doesn’t lend itself to an off-the-shelf header solution, you’ll have to fabricate your own set. You can find yourself in this position if you’re working on an engine swap of some kind, or have a custom build that has space restrictions.
Before you cut a single piece of tube or fire up the tig welder, you’ll need to assess what could get in the way of the headers. Any chassis restrictions, oil system plumbing, accessory location, along with a host of other factors are going to influence where you can place a set of headers in the engine bay.
“Unless you’re racing a dragster with all the space in the world, the chassis will dictate what you can and cannot do when designing a set of headers. In N/A applications where header sizing is incredibly important, you’re still only able to work with what you have. The idea is to make the best of it and build a header that performs well given the space allowed,” Filippides states.
The initial planning phase of building a set of headers for a naturally-aspirated build also needs to take the engine combination itself into consideration. Headers are going to have a big impact on how the engine performs through the power band — the last thing you want to do is build a set of inefficient headers for a naturally-aspirated engine.
“First, think about if you should use a single primary size tube or use a stepped header design for your engine. High-RPM N/A combinations typically love a stepped header design because the smaller size helps lower torque numbers, while the larger size compensates for the high RPM horsepower numbers. It’s a best of both worlds scenario as long as it’s sized accordingly and the proper collector size is used,” Filippides says.
After you’ve looked at where the headers need to go, decided what style you need, and how big they’re going to be, it’s time to plan out a design for the headers. If you just start welding tubing together with no clear vision you’re going to have problems finishing the build.
“The best fabricators in the world are those that can envision a design before even starting it. Mentally figuring out tube routing before cutting any metal helps tremendously. It ultimately helps to save you time and material. Routing three tubes and then learning that there isn’t enough room for the fourth is incredibly frustrating and will force you to start over. Patience is key in fabrication and only leads to better end results,” Filippides explains.
If you really want to get the most out of your naturally-aspirated engine you’d better be ready to spend some time researching headers. There’s a lot more than just tube size to think about, and making the right choices will ensure your naturally-aspirated engine has plenty of rip throughout its entire powerband. Make sure you follow Project Number Cruncher right here to see all the progress we’re making with the car.