Larger throttle bodies, ported throttle bodies, and throttles of different design are commonly sold as a performance upgrade for your vehicle. Many people jump down this modification path, since the factory throttle bodies on many vehicles are what they would consider "Small"; commonly 70mm, and even smaller.
After installing an aftermarket throttle body, assuming the ECU can control it, you'll feel an instant seat-of-the-pants change in how much power the car is producing around town. It's easy to see why this modification has been so prolific.
Does it actually add power??
The throttle body's intent is to restrict airflow and limit how much power the motor will make, for those times when you do not need *ALL* of it. The question is, at full throttle, is the throttle blade a restriction to power production?
The further you open your throttle blade, the more air will be able to pass through, making more power. This is applicable driving around town, as well as on the track.
If you change the diameter, or size of the throttle blade, when you push down the accelerator, you are allowing proportionally more air into the motor than your factory throttle body.
While you may have had 1 square centimeter of open area at 5% throttle before, with a new throttle blade, you may be at 1.5 square centimeters of open area, letting the motor make 50% more torque at that same 5% throttle opening.
The additional perceived power is equivalent to you pressing the throttle further down anytime you drive. You're choosing to let proportionally more air in, but that doesn't necessarily mean that the modification made the motor more efficient or more powerful-- It's just being driven harder.
When do I need an upgraded throttle body??
As always, "It depends"...
If the throttle body is a restriction to the rest of the intake, upgrading it to a larger throttle body will deliver a performance increase. Typically, the largest restriction is going to be the size of your vehicle's intake valve, and increasing the size of the throttle body will not be beneficial.
Fortunately, it's incredibly easy to log whether or not the throttle body is a restriction. Since the throttle body is a valve to limit how much air pressure (volume) is inside of the manifold, compared to how much air pressure is in the atmosphere, we can log both variables and see if the throttle is restricting airflow.
Here's an example of a vehicle where the throttle is not a restriction This is a 98 LS1 Camaro, with a full exhaust, and BTR Stage 3 cam. With the key off, we were seeing a Manifold Absolute Pressure reading of 95kpa, which was atmospheric pressure for that day. During a WOT pull, if pressure in the manifold drops below atmospheric pressure, that indicates a restriction in the throttle body or the intake tube.
As you can see, the MAP reading (Light Blue) stays right in line with the dashed ("-----") reference line, through first gear and most of second gear while the vehicle is wide open throttle. There is no restriction to remove by increasing the size of the throttle body
Here's another example, where the throttle body actually was a small restriction This car had a larger than stock intake tube and filter, so we know that the bottleneck factually would be the throttle blade and not another component. This is a manual LS3 Camaro, with full exhaust, and a massive TSP F35 cam.
On this log, we measured atmospheric pressure at 97kpa, and the dashed reference line reflects that value. As you can see, towards the top of the gear, the motor is able to pull the manifold into a slight vacuum, at 94kpa. While not a significant power loss, this tells us that the throttle blade *IS* a restriction in this application.
It's time to upgrade. What should I pick??
Quality matters, if how your car drives is important to you.
Drive by Cable
If you have a vehicle that is Drive By Cable, your ECU is less sensitive to quality differences.
The biggest problem to watch out for with a drive by cable upgraded throttle body is Idle Air Control. Many aftermarket castings have poorly engineered passages for IAC operation. If the IAC passage does not seat (close) well, or does not provide enough volume of airflow, we have problems getting your vehicle to idle well, and there's typically nothing we can do to fix that.
On LS motors, we've had problems with idle control on large cams with apparent FiTech throttle bodies, as well as the common "Sniper" / "Jegs" / "G-PLUS" / "Kyostar" casting pictured below.
A motor needs more airflow to maintain idle speed, until it is up to temperature. With these castings, we've often only been able to hold 700-800rpm at 70* coolant temperature, with the IAC all the way open. When we are up to temperature at 210*, the IAC is completely closed, and we'd be idling well at our 850rpm target. There's nothing I can do in a tune to provide more cold-start idle airflow, if the IAC is already all the way open.
Drive by Wire
Electric Throttle Controlled vehicles use the throttle blade for idle speed control. There is no longer a dedicated Idle Air Control valve. When you change the amount of open area that the throttle provides with each degree of rotation, the ECU is no longer able to control idle speed with the factory calibration. This is felt as surging or stalling.
The airflow models used to define electric throttle bodies are not linear or mathematically simple. In many applications, you can't get anywhere close to the correct values by multiplying the airflow models by the percentage increase in throttle size. This is especially problematic if you move from a round throttle to a large oval mono-blade or something of different shape.
Idle control with an aftermarket DBW Throttle, without data, is problematic. It can be achieved, with a lot of time, however, there will always be minor drivability issues from the parameters in the ECU being "Close" and not "Correct".
Consider other factory throttle bodies that may fit your sizing needs, which will have published data available. Your tuner will be able to input the airflow modeling data from your new throttle, and your car will idle and drive like it does now, without the restriction.
If you'd like to know if we feel a Throttle Body is a good upgrade for your vehicle, or if you'd like suggestions of throttle bodies to upgrade to, please reach out to us! We want to make sure you get the best bang for the buck, and end up with a vehicle you love to drive.