How to Measure the Diameter of a Throttle Body

by Tim Petruccio
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The throttle body on an engine is the body that controls airflow into the engine, in regulation with the amount of fuel also being dumped into the engine. The throttle body valve opens when you depress the gas pedal, allowing more air to enter the engine, along with an increase in fuel. There are two variable diameters on a throttle body. The first diameter is the inlet diameter, and the second is the throttle body bore diameter. Throttle body locations will vary between vehicles.

Measuring Inlet Diameter

Step 1

Open the hood of your vehicle, and visually locate the air intake tube. The air intake tube runs from the air filter housing to the throttle body.

Step 2

Remove the air intake tube, using a 3/8-inch drive ratchet and socket to remove the clamps. Slide the air intake tube off of the engine once the clamp is loosened. (Some vehicles have a spring wrapped around the intake tube on the throttle body. These intake tubes can be removed by hand.)

Step 3

Measure the inner diameter on the front of the throttle body. Place a measuring tape against the inlet hole in the throttle body, and take a measurement of the inside of the throttle body inlet. This measurement is known as the inlet diameter, and is a good measurement to have if you are fitting a cold air intake or supercharger to your current engine.

Write the measurement down on a piece of paper. Use a S.A.E.-to-metric converter if you are dealing with a foreign throttle body. Throttle bodies on foreign vehicles are measured in millimeters, not Standard American English measurements. You can find a free conversion program online through your Internet search engine.

Measuring Throttle Body Bore Diameter

Step 1

Remove all air intake components from your engine, using a 3/8-inch drive ratchet and socket. The exposed engine part on the engine side of air intake is called the throttle body.

Step 2

Remove the four mounting bolts that hold the throttle body in place, using a 3/8-inch ratchet and socket.

Remove the throttle body using a small pry bar or flat head screwdriver. Turn the throttle body sideways if it is a vertically mounted throttle body. Measure the holes or ports in the bottom of the throttle body. When measuring the ports, you are measuring the bore diameter of the throttle body. The bore diameter is the inner diameter of the bore on the engine side of the throttle body.

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