Individual Throttle Bodies – A Great Way To Boost Performance?

In the world of engines, no approach is too insane when it comes to boosting its output, and eking out every ounce of horsepower available. Whether it’s fitting a high flow catalytic converter in the rear, or considering a cold air intake up in the nose of the car, every avenue of possibility is worth thinking of if maximal performance is your ultimate goal. But what about a set of individual throttle bodies?

The throttle is a part of the car that isn’t often thought much about when it comes to tuning. Turbos, intakes, camshafts, or perhaps an ECU tweak are the most popular mods that folk bolt onto their cars. However, as the throttle body is the item that controls the amount of air going into the engine, maybe there’s some potential to be had there. Nevertheless, are individual throttle bodies worth it?

• What Is A Throttle?
• How Does It Work?
• How Many Bodies?
• Benefits
• Downsides
• Horsepower
• How Much For It?
• Factors To Consider
• Final Thoughts

What Are Throttle Bodies, Anyway?

Individual or not, a good place to start is discussing what throttle bodies are in the first place. So, what is it that they do in your car? For a spot of context, your engine needs two key items for internal combustion to occur – fuel, and air. Pumping fuel into the engine is a complex process in of itself. At the very tip of this machination are the fuel injectors, which spray fuel into the combustion chamber.

So, how about the air? We all know that engine-powered cars have large intakes up in the front, and this is where fresh oxygen is directed into the engine. Mind you, your car’s intakes are merely there to guide the air in. What they can’t do, however, is allow the fresh atmosphere to pass into the engine to be ignited with the mixture of fuel. This is where throttle bodies come in, as part of the intake system.

You can find the throttle body usually sandwiched between your car’s air filter up in the front, and the intake manifolds behind it. The throttle body is responsible for one thing – permit air to pass through into the engine. Subsequently, it’s also responsible for controlling how much fresh air can enter, based on input from the accelerator (or throttle) pedal. The throttle body appears like a stubby tube.

Inside, there’s a flat, pivoting, butterfly valve. This is what opens and closes to let in however much air that’s deemed necessary. Press the gas pedal harder, and the valve opens up even more. Thus, higher volumes of air can flow into the engine, and combined with more fuel, this dense mixture can create a more potent explosion. On the flipside, depressing the gas pedal will close off more of the valves.

How Do Throttle Bodies Work?

The throttle body can be controlled in one of two ways:

• In older cars, the throttle bodies are linked directly to the gas pedal, by way of a throttle cable that is connected straight to the throttle linkages. This mechanical connection is especially true in much older carburetor-powered cars, where the throttle bodies are built into the carbs. The valve is actuated by way of a direct connection to the pedals, as well as using engine vacuum.
• With newer cars and their electronic throttle controls (or drive-by-wire), the throttle bodies are linked to electronic actuators. Instead of a direct connection to the accelerator pedal, this actuation is paired with a series of sensors. In particular, the throttle position sensor (telling the car’s computer that the gas pedal was stepped on), and the mass airflow sensor (detecting the precise amount of air flowing in).

These two methods – a mechanical connection through a cable, or electronic signals – will regardless, correlate the position of the gas pedal, to the opening (or closing) of the throttle body’s inner valves. In most vehicles that you encounter today, electronic controls – including some assistance by the car’s ECU – are commonplace. You’ll still find mechanical throttle bodies in many surviving classic cars.

Nonetheless, even these mechanical connections had some electronics in them. For example, it needs to maintain at least some opening while the car is idling, and your foot is off the gas pedal. Otherwise, the engine would stall altogether. Thus, you can crack open vintage throttle bodies, and find a small solenoid-driven valve. That’ll keep the bare minimum amount of air flowing in, even as you’re idling.

How Many Throttle Bodies Are There In A Car?

You’ll notice that we regularly exchange “bodies” with “body”, and that’s by intention. Most cars likely feature just a single, large throttle body. Just one unit is more than sufficient to keep air flowing into the engine. With that being said, a single point of entry may prove to be a significant bottleneck in your engine’s potential output. Hence, why some vehicles have numerous bodies.

Hence, the term ‘individual throttle bodies’ comes into play. With more performant vehicles that need a lot of power, be it heavy-duty trucks or sports cars, they need more than one throttle body. Albeit, this is fairly uncommon. Some of them feature one throttle body for each bank of cylinders. You’ll find this on vehicles that have large displacement engines. Or, maybe one throttle body for each cylinder.

In some vehicles, they may have just a single throttle body, but with two smaller openings and valves, instead of one big unit. Each configuration presents its own set of pros and cons, sometimes for the benefit of improved performance, or is more cost-effective. However, the inclusion of several throttle bodies instead of one is rare. This is given their expense, and it’s unnecessary on most vehicles.

With that in mind, note that when one mentions ‘individual throttle bodies’ (or ITBs), we’re specifically highlighting a layout whereby each cylinder gets its own throttle body. Therefore, if you have a V8, there ought to be 8 smaller throttle bodies exclusively for every cylinder. Moreover, using individual throttle bodies means that you could theoretically remove the need for intake manifolds altogether.

What Are The Benefits Of Individual Throttle Bodies?

The core principle of ITBs does have its merits. With a single throttle body shared among all cylinders, the air has to travel much further from the intake to the combustion chamber. As a result, this slows down your engine’s throttle response. Using individual throttle bodies, on the other hand, enable the air to build up the pressure just outside the cylinders. Press the gas pedal, and air rushes in instantaneously.

Lacking any delay or travel time for the air entails speedy throttle response, with non-existent lag. Besides that, here’s a TL;DR list of the myriad of benefits that individual throttle bodies can offer you:

• Hastier Throttle Response – We talked about this numerous times here already, and there’s certainly a pronounced swiftness between when you press the gas pedal, and the engine cranking out power.
• Additional Power – Since air is can fill the combustion chamber more quickly, and with fewer obstacles in the intakes, individual throttle bodies do result in increased horsepower. More on this later.
• Improved Airflow – Using throttle bodies, as we mentioned earlier, can allow you to remove the intake manifolds completely. The key upside here is improved airflow, as fresh atmosphere can be sucked into the engine directly.
• Better Noise – Intake noise is underappreciated in today’s crop of performance cars. Using individual throttle bodies means fewer things getting in the way, such as the intake manifold. The effect is hearing that wonderful sound of air surging in, and the mechanical actuation of the throttle bodies in action.
• Looks Cooler – While not entirely functional in this regard, using individual throttle bodies does make your engine bay look ten times more awe-inspiring. Seeing those trumpets sticking out will certainly make a great conversation piece. If anything, your car “looks” faster with them on.

What About The Downsides Of Individual Throttle Bodies?

For all the advantages that individual throttle bodies offer, there are undoubtedly substantial caveats that you have to consider. Here are some of the most notable cons of fitting ITBs:

• They’re Expensive – We’ll be discussing more later on, but individual throttle bodies are a costly modification under any circumstance. A quality stack of ITBs could run you at least $1,000 (though it’s often much more) and is an intensive addition to bolt onto your car.
• Negligible Benefits – As we’re going to uncover this soon, individual throttle bodies do add power. Still, it’s worth mentioning that what horsepower gains you may extract with ITBs need to be proportional to modifications you’ve made elsewhere. Otherwise, you could be spending a lot of money for what may end up being single-digit horsepower gains.
• High Maintenance – This only applies if you’re removing the entire intake plenum and manifolds when performing an ITB installation. Without the manifolds there, the throttle bodies may be susceptible to attracting much more dust, dirt, and other contaminants. Hence, you’ll need a throttle body cleaning more frequently, as there isn’t enough filtration.
• Too Loud – We’ve harped on the glorious intake noises that the addition of individual throttle bodies may grace us with. Nevertheless, and if done up a bit too much, it can prove to be too loud. In some regions, ITBs may be far too noisy for regular road use.
• Unable To Run MAF Sensors – Mass airflow sensors typically require an enclosed intake system for it to correctly measure the volume of air flowing into the engine. This, once again, applies only to cases where the intake plenum is removed, but it does negate the use of MAF sensors.

Do Individual Throttle Bodies Add Horsepower, And How Much?

There are good reasons why individual throttle bodies have become so popular on high-performance cars. Think of the Nissan Skyline GT-R, BMW M3, or countless other thorough thoroughbred race cars. ITBs, when tuned properly and complemented with other engine modifications, could positively affect your car’s performance. Alas, the isn’t a one-size-fits-all example, the results will differ greatly.

For instance, a big block American V8 with an abundance of excess displacement to play around with could yield up to 100hp or more with the addition of individual throttle bodies. The results, however, are generally more modest with cars using smaller engines. Four-cylinder motors, for example, could only net you an extra 30 to 50hp on the dyno, even with highly-strung individual throttle bodies.

These figures aren’t a given, and this leads us to a crucial point that needs to be made – ITBs aren’t the end all be all of the performance modifications. In fact, most tuners agree that ITBs should be added in as a finishing touch on your project car. Not, as some might suggest, as a starting point to extract your engine’s true potential. Individual throttle bodies should be matched with other mods to work well.

Examples of these supporting tune-ups to be done in addition and alongside individual throttle bodies include (but aren’t limited to):

• Airflow improvements, such as a cold air intake
• Porting the cylinder heads to open up a more efficient airflow
• Performance camshafts to optimize the combustion process
• ECU mapping to program in tweaks for more power
• Exhaust headers (or a sporty manifold) to get air moving in and out quickly
• Forced induction, either a turbocharger(s) or supercharger

How Much Do Individual Throttle Bodies Cost?

So, you’ve seen now what you’re getting with individual throttle bodies. But for all the horsepower or throttle response enhancements, how much will it cost you in return? As we highlighted briefly, a set of decent individual throttle bodies will cost you at least $1,000. That’s not to mention any other mods that you’d like to perform in concert with these new ITBs, in maximizing its potential gains.

Despite that, most individual throttle bodies cost a lot more. Typically, the starting price is around the $2,000 mark for a modest bump in power. Go for a fully kitted-out set, and don’t be surprised if a $5,000 bill for a set of ITBs is handed to you. This will all vary immensely based on how your car is set up, as well as the make and specification of the individual throttle bodies in question.

In stark contrast, a single throttle body setup often costs somewhere between $200 to $600 for a full replacement job. That includes parts and labor. On average, you can expect an equivalent individual throttle body for your car to cost 3x to 6x more than a singular unit. This lofty expense is attributed to the precision and attention to detail required while machining a set of individual throttle bodies.

What Are The Factors Of Individual Throttle Bodies To Consider?

Before you go out and get a set of individual throttle bodies, there are important considerations besides the price tag. You’ll have to think about the amount of room around the engine bay and see if the bodies can even fit, in the first place. Next up, have a moment to think about the potential impacts on emissions, fuel economy, running costs, future modifications, as well as the sound.

Finally, you’ll have to take a step back to wonder over the right size of individual throttle bodies that are right for your car. This is crucial, as not all throttle bodies are configured and shaped the same. Thus, why individual throttle bodies optimized for a certain car might not play well with others. You’ll need to take into consideration the cylinder count, total output, as well as engine displacement.

Here’s a very basic general guideline for which sizes of individual throttle bodies might be the right fit for you. Note, cfm refers to the ‘cubic feet per minute’ of intake, taking into account both the volume of air and fuel. Meanwhile, the cc (or ‘cubic capacity’ is measured by a per-cylinder basis).

• 40mm ITBs – 265cfm, 61hp gain, 350-500cc/cyl
• 42mm ITBs – 304cfm, 70hp gain, 450-600cc/cyl
• 45mm ITBs – 362cfm, 83hp gain, 550-700cc/cyl
• 48mm ITBs – 408cfm, 94hp gain, 650-800cc/cyl

Besides that, here’s a more detailed guide for all the different bits and pieces that make up individual throttle bodies. Furthermore, what factors and variables that go into their design or layout should be considered?:

1. Inlet Tract Length

This refers to the gap between the inlet valve (where air surges into the engine), and the end of the trumpets (where the ITB receives the air). The inlet tract length can have a monumental impact on air speed. Should you use an inlet tract that’s too short, for example, it will result in a loss of power.

Or, at least, not being able to optimize the potential power gains. Most tend to make this mistake, by using under-length individual throttle bodies. What you get in return for adopting too short of an inlet tract length, is that peak torque and max power move further up the rev range.

Sometimes, too high up to a point where the engine can’t reach them without being overly worked. In short:

• Longer inlet tracts are capable of cranking out more torque, with power generally being optimized at the middle of the rev range.
• Shorter inlet tracts will move the peak horsepower output and max torque up in the RPM range.

As a whole, longer inlet tracts are commonly regarded as the optimal setup. However, they’ll require a lot more clearance in the engine bay to accommodate the elongated trumpets. Other than that, you can optimize the inlet tract length with varying sizes of trumpets and manifolds, or use spacer plates.

2. Taper Or Parallel-Type

Throttle bodies come in two types – tapered or paralleled. Specifically, it references the diameter of the butterfly valves. With a parallel body, both sides of the throttle body are of similar dimensions. Meanwhile, a tapered body will sport a smaller diameter opening on the engine side.

Hence, the pronounced and wide extensions of the trumpets on the outside. The use of a tapered body does result in a more constant and proportional increase in air speed. As the diameter of the opening gets smaller on the other side, it creates a ram effect that gradually ramps up the air speed.

3. Trumpet Dimensions

The trumpets (or stacks) have been designed specifically to make it as easy as possible for air to start rushing through. Know that in the engine, there’s a substantial pressure difference between induction pressure inside the engine and the atmosphere outside of the motor.

ITB trumpets are tapered in a way to allow air to transition through that pressure differential more efficiently. Hence, why the opening of the trumpet has a wider diameter than the inlet valve of the throttle body. Furthermore, the trumpet has to prevent excess turbulence or airflow disruptions.

Just like the inlet tract length, the dimensions of the trumpet length-wise can affect performance, too. Similarly:

• Longer trumpets generally yield more torque and power peaking out mid-range.
• Shorter trumpets move the torque and power higher up in the RPMs, which is very suitable for high-revving engines.

4. Positioning Of The Butterfly And Fuel Injector

Then, you’ll have to fine-tune the gap between the butterfly valves, as well as the fuel injectors. This is where the fuel and air get mixed in, before ultimately ending up being compressed and ignited in the combustion chamber. Positioning them correctly is key to maximizing performance:

• If they’re too close to each other, it won’t give them enough time or room for fuel and air to mix. At low speeds, you won’t notice it. But once you get going quickly and at higher RPMs, performance may be compromised.
• If they’re too far from each other, there’s too much empty space that the mixture of fuel and air have to travel across. This echoes the flaws with using a single throttle body, where reduced air speed will result in delayed throttle response.

Typically, most vehicles have the fuel injector ports situated as close as possible to the throttle body’s inlet. In effect, this ensures potent performance at lower RPMs, good fuel economy, as well as lower emissions. Some cars may have more than one fuel injector per throttle body for a healthier balance.

They’d install the fuel injectors closer to the butterfly valve, near the engine. This way, you’ll get a lot more turbulence, which helps air and fuel to mix more thoroughly. It results in a good performance that leans more towards the higher end of the rev range, not to mention a heightened throttle response.

5. Roller Barrel Or Slider Throttles

There’s another, more unique style of throttle bodies. Unlike their butterfly-actuated ones, these use either a roller barrel or slider door mechanisms to open and close. The key design flaw with butterfly-style individual throttle bodies is how the valve flips open and stays put in the middle.

Even at full throttle, the butterfly door is an obstruction where the air has to maneuver around it. This results in some turbulence. Roller barrel or slider throttles, on the other hand, leave no obstacles for the air. It’s a divisive topic, but many agree that these two typically work better at full throttle.

Individual Throttle Bodies: Facts You Need to Know

• ITBs involve using a separate throttle body for each cylinder, with a vacuum line running from a vacuum box to each intake runner.
• With ITBs, there’s a more direct and identical path for air to reach the inlet ports, resulting in improved throttle response and increased power.
• ITBs are expensive due to the increased complexity of having multiple moving parts.
• Aftermarket ITBs can be costly, adding only around 20bhp and are worth considering for those determined to increase power without forced induction.
• ITBs are commonly seen on more exotic performance cars such as Ferrari and BMW’s M Division naturally-aspirated engines.
• ITBs improve the looks of an engine and produce a throatier engine note.
• ITBs are not common on production cars due to the cost of mass production.
• The conventional setup with a single throttle body allows air to travel a longer distance to reach the inlet ports, which varies for each cylinder.
• ITBs are the ideal setup for naturally-aspirated tuning, offering improved power and response.
• The SR20DETT engine found in the Pulsar GTI-R has individual throttle bodies despite having only a single throttle setup in the S-chassis models.

Final Thoughts On Individual Throttle Bodies

Well, there you have it, most of what you need to know about individual throttle bodies. You might be asking, then… Is this a worthwhile upgrade to shill your hard-earned cash on? Truth be told, any mods around throttle bodies shouldn’t be done individually. Only once you’ve installed a bucket load of bolt-on modifications to up your car’s pace, only then could you think about individual throttle bodies.

As you’re tacking on more performance tune-ups, the one major bottleneck left solving is the throttle body. Only then, could such an expensive, sell-your-kidneys investment be considered to attach a set of individual throttle bodies together. Otherwise, the cost is far too high to satisfactorily justify any gains from those individual throttle bodies. For much less, you can’t go wrong with a pair of turbos.