Exhaust Headers & Fuel Economy: Why Headers Improve Mileage

Exhaust Headers & Fuel Economy

The increase in engine performance is one of the most important reasons why many car enthusiasts choose to install a high-performance exhaust manifold or header system on their vehicle. Without a doubt, this equipment provides a healthy boost in power output and torque. However, if you don’t know some basics about how these components operate under different conditions, you could be sacrificing your gasoline mileage for nothing.

Mileage Losses from Headers

In order to understand what causes lower mileage with headers installed, it’s necessary to have at least some general knowledge of how exhaust system components work together to move spent combustion gases away from an engine’s cylinders. This process is accomplished by routing the gases through a series bends, lengths and diameters that creates enough turbulence to insure the gases are cooled and mixed with fresh air, before they are finally expelled through the tailpipe.

Since engine performance increases significantly when header diameters are reduced to lessen back pressure, it’s easy to understand why many enthusiasts mistakenly believe that this type of equipment will provide increased mileage because of improved cylinder scavenging. It is true that less resistance will result in more efficient combustion, but just how much power you stand to gain by improving your exhaust system’s flow capacity depends on far more variables than just tubing size or length.

The Power Loss Myth

A lot of rumors have been flying around for years about so-called “power loss” caused by headers, which has led some people to question whether these components will decrease the mileage of their engines. However, whether or not this occurs is heavily dependent on the design of an engine’s cylinder head(s) and intake manifold rather than the tubing diameter or length of a header system.

The truth about power loss caused by headers comes down to one simple fact – there is no power being lost through your exhaust system unless your engine’s overhead valve (OHV) or pushrod valve actuation systems are poorly designed. As long as the intake and exhaust valves open at “parallel angles” when they are both fully opened, there will be an overall increase in horsepower with any given gasket thickness between the two components. For example, if you were to keep your pushrod diameters the same while reducing an intake manifold’s gasket thickness from .040″ to .030″, you should experience a net gain in power.

However, if your engine’s intake and exhaust valves operate at different angles when they are both fully open (i.e.; intake opens first or exhaust opens first), then theoretically there will be no change in horsepower between the two set-ups as long as the valve timing remains the same. In this case, depending on how much power is being lost through increased back pressure from a thicker gasket, there could be a slight increase by going down to a thinner one. Just remember that many factors can affect how an engine performs – including camshaft design and rpm range – so it still doesn’t mean mileage gains with less resistance.

Reduced Back Pressure Improves Mileage

As a general rule, as long as your engine’s valves are operating at “parallel angles” and you’re going with a thinner gasket, there will be an increase in power output and torque with the same diameter header. This typically occurs because there is less back pressure caused by a combination of improved scavenging around the exhaust valves and more turbulence to create a better air/fuel mixture for burning. Keep in mind that these two factors aren’t mutually exclusive, so unless it interferes with other aspects of your engine’s performance, cheaper is always better when it comes to choosing exhaust components – especially headers or manifolds. In some instances where fuel mileage may not be what you expect from using a more efficient exhaust system, it may have more to do with the type of fuel being used rather than the power gain or loss that you might experience.

A Better Combustion Chamber Makes More Power

When you’re buying headers for your street rod, muscle car or performance vehicle, there are certain key factors to look for. This starts with checking our the engine’s compression ratio by measuring the cylinder head thickness at its base where it meets the deck surface of each cylinder. From this alone, you can get an idea if there is enough open space inside for adequate airflow between each runner and around all valves when they open. For maximum performance in most conventional truck engines (non-hemi), we recommend at least .100″ thick deck surface on the cylinder head at its base. As a rule of thumb, smaller cubic inch engines typically have lower compression ratios – which means less back pressure – while larger cubic inch motors may run higher compression due to their combustion chamber size and overall engine design.

If you’re more concerned about fuel mileage, look for header systems that are ported with smooth transitions from the primary tubes into the collector area around each exhaust port or valves. Porting is also beneficial in terms of reducing restrictions when it comes to air flow that can get trapped inside the tubing, which can boost how much power your engine makes. Another key aspect of performance exhaust components is the way they are joined together using gaskets, clamps or other couplings so there isn’t any leaks around the header system.

In this particular case, where the motor moves from a free-flowing intake manifold to a restrictive exhaust system on a stock truck engine, there will be a power loss – although it may only result in one mpg compared to going with the same size header and thicker gasket. In which case, you would have more of an issue with fuel mileage versus performance since any potential power gains are negligible. The key is to get your motor running as efficiently as possible by optimizing its air/fuel ratio while also eliminating back pressure for higher power output that doesn’t cost you at the pump.

The Pros & Cons Of Using A Milder Compression Ratio On Small & Big Block Chevy Engines

Small block engines with a 10:1 compression ratio and bigger cubes with 8:1 typically run better with less restrictive headers – which means they also tend to get slightly better fuel mileage compared to going with a high performance, free-flowing exhaust system. This is due in part because most truck engines come from the factory running between 8:1 and 9:1 compression ratios across the board, so using a lower grade of octane (87) isn’t as likely to cause detonation or knock when making power.

Although there are benefits when it comes to using high flow cat converters that can improve horsepower and torque on engines running around 9:1 and up, there’s always going to be an increase in back pressure by comparison. As such, dropping the overall compression ratio on a smaller cubic inch engine with a stock exhaust manifold doesn’t allow for optimal performance gains. In most cases, you’ll see around a 5-10 percent increase in fuel mileage when going with headers and a high flow cat converter system – if that’s more your goal.

However, the more open space there is between each header primary tube and runner length along with its general design without too much restriction means higher horsepower numbers once you’re under the hood. As such, headers will give any small block an octane boost by allowing more air/fuel mixture into your combustion chambers for better throttle response and acceleration – not to mention less strain on the valves while getting up to speed.

On the flip side of this, using high performance headers to power a big block engine with a low compression ratio can get you into more trouble over time depending on your driving habits. In the case of an 8:1 or less compression ratio, detonation from too much throttle at high RPM is going to be more likely compared to using a high performance header with your stock motor – although it may not be noticeable while cruising down the road.

By comparison, taking a smaller cubic inch engine that typically runs around 9:1 and going to 10:1 can result in hot spots for knocking since there’s no octane boost from the spray pattern used by fuel injectors. Although this isn’t always dangerous when it comes to tuning, higher compression ratios paired with lower octane fuel could cause engine failure after prolonged use – especially when you’re constantly opening the throttle to accelerate at every stop.

Your engine’s compression ratio isn’t something most car and truck enthusiasts think about until an issue starts popping up. However, knowing what it means for your vehicle in general can help with setting a goal for making changes down the road along with getting more out of your ride in between tune-ups over time.

Engine Compression Ratio: What It Is & How To Maximize Your Power Potential With A Low (Or High) Grind

If you own a performance vehicle, chances are you’ve done some research on aftermarket parts for it. Chances are also high that at some point along the way, you came across something about the compression ratio – what it is and how it affects your engine’s efficiency. For those who don’t know yet, here’s a quick primer.

The compression ratio of an engine is defined as being the relationship between its total cylinder volume at BDC (bottom dead center) versus its clearance volume at this same point. This means that essentially you’re taking into account all space within each cylinder to find out how much air could theoretically be held in place under normal circumstances assuming 100-percent efficient seals.

For example, if you have an 8-liter engine with a compression ratio of 8:1, the volume of each cylinder while at BDC would be 125.59 cubic centimeters (8 x 125.59 = 1000) while its clearance volume would only be 25.18cc (.8 x 25.18 = 20). Once you divide 1000 by 20 and get your answer (50), it means that on paper, this common V-shaped internal combustion engine is capable of holding 50 liters of air under normal conditions – although there’s quite a bit more to this equation than meets the eye.

How Does This Affect Performance And Fuel Mileage?

Knowing your engine’s compression ratio can help determine what kind of performance results drivers can expect from their vehicles before ever taking them out on the open road. Although a higher compression ratio enhances throttle response and acceleration, it also results in a little less fuel efficiency compared to what you can expect from a vehicle with a lower number.

This is mainly due to the fact that as you go up with compression, so does the amount of heat generated within each cylinder along with having more space between each chamber for combustion – both of which result in burning your fuel at a hotter temperature than usual. Most engines operate under this cycle where they’re designed around a specific ratio to ensure optimal power output without needing to run high octane gasoline all the time. On average, most modern internal combustion engines have a compression ratio range between 7:1 and 9:1 depending on their application and design – although this doesn’t necessarily mean you can’t make modifications to go beyond this number.

If your engine is running under a higher compression ratio, chances are high that it wasn’t originally designed for this modification and could have some major problems with burning fuel or even knocking as a result of going down this route – especially if you’re going from a low compression ratio to a significantly higher one. Again, although most performance engines today handle a large range of compression ratios, making changes based on the manufacturer’s suggested specifications will always have the best outcome in terms of reliability versus risk.

In contrast however, using an engine with lower compression but adding octane boosters to compensate can result in better performance along with more horsepower without ever having to modify anything else. In a sense, you can think of this as creating a load-bearing beam for your engine that helps to maximize power output while minimizing the possibility of damaging anything. Again, not much is needed in terms of additional changes when using an engine with lower compression ratios – although if you’re going from a higher number to a much lower one, it’s best to simply find another vehicle and start over instead of trying to drop your compression artificially.

What About Higher Compression?

When talking about high compression engines, we usually refer to these as being turbocharged or supercharged where they have specially designed cylinders and pistons that provide more space for air intake without having to push the limits on what their original design was intended for. These setups also come with specially designed valves and other components that allow for increased air flow while helping to reduce the amount of heat generated through combustion.

A lot of people believe that compression ratios are only good for increasing performance; however, this is simply not true. While it’s true that higher numbers will enhance throttle response and acceleration, it doesn’t mean that your engine won’t get better fuel economy like what you can get with lower compression engines or even naturally aspirated ones – something we see on many diesel trucks today.

These setups also come with a whole new set of challenges including added risk factors such as thicker cylinder walls and having to keep track of how much turbo lag is involved when taking off from stoplights or pulling away from a dead stop in general. Since these are all very important factors to consider when choosing the right vehicle, trying to run high compression ratios with lower octane gasoline could cause all sorts of potential problems.

The benefits of adding a set of headers to your car:

High performance engine parts such as headers and long tube exhausts come with a whole host of benefits including better airflow, higher torque and horsepower ratings, improved fuel economy, and much more. Since the function of these parts is to make your engine more powerful by creating less backpressure while also improving gases in general, you can expect a nice improvement when it comes to overall power output without any real risk factors.


When it comes to improving fuel economy, you have to look at what’s causing your vehicle’s poor fuel consumption in the first place. One of the main factors that leads to decreased mileage is backpressure caused by performance engine parts such as manifolds, catalytic converters, and mufflers. Since these are all designed with specific functions in mind, having them on your car is better than nothing – however, they do impede airflow without really doing much about gases themselves.

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