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VAP Tech Article 1: Maintaining Throttle Body Geometry
Steven Franker - 9/26/09
 

The 01-04 throttle bodies have a plastic cable pull end that features variable radius geometry for a more linear pedal feel compared to the 99-00 fixed pivot style.

In order for the throttle body to work with the Windstar intake and remain under the stock hood the cable pull attachment must be controlled from the side of the intake. This is accomplished by welding a extension arm onto the throttle body and relocating the attachment end of this arm.

A few of my early throttle body modifications suffered from poor geometry, sometimes resulting in a throttle body that would only open part way. In an effort to increase hood clearance it was easy to unknowingly compromise the throttle geometry and increase the pedal force dramatically.

In order to make sure each and every throttle body I modify has the correct pedal force I've done a careful study on the geometry of the 01-04 throttle body. The results are somewhat surprising. The chart below shows the relationship between the throttle opening and the corresponding pedal force.

The green line represents a throttle attachment end that was positioned just 1/4" off center from the stock position. If the radius of the throttle curve is brought closer to the axis of rotation the effective leverage quickly decreases and the pedal force shoots up.

A new throttle arm location was optimized to maintain hood clearance and to approximate the OEM pedal force. As you can see from the chart the new "VAP" optimized throttle arm location closely follows the OEM force curve throughout the full range of motion.

In order to constantly position the throttle arm for welding an accurate jig was required. After modeling the throttle body in 3D CAD a jig could be built around it that would position the new CNC cut attachment mounts in the perfect location relative to the throttle body's rotational axis. Built from solid aluminum with a tolerance of +-0.005" the new jig and attachment plate provides constant results and a smooth pedal feel every time.
 

The New Throttle Body Jig, CAD Rendering

Analysis of the TB Geometry



The New Throttle Body Jig in Action

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