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Throttle Body & Pulley Swap: Finding Those Last Few Horses

Posted in How To on March 1, 2012
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Photographers: Jason SandsKimson Ekman

It must have been fun, back before emissions testing became the norm. Truck buyers were able to open their hoods and rip right into the engine, creating whatever kind of steroided-up Detroit-iron monster they wanted. Try that today and not only will emissions clearance be a problem, but the computer brain of the vehicle will likely throw a hissy-fit and disable the vehicle if not reprogrammed properly.

Thankfully, the aftermarket is always quick to come up with solutions for the modern power-obsessed vehicle owner. Companies like BBK Performance are constantly designing and testing parts designed to help engines reach their optimal potential. In some cases, this is accomplished by taking heat or strain away from the engine in order to limit the parasitic effect that load and temperature can create—things that tax the engine and rob it of power. In other cases, as most of us understand, power can be gained by simply helping the engine to accept all the air it can use. Recently, we got the chance to try both strategies when BBK sent us their Twin 56mm throttle body (to help the engine breathe) and Power-Plus underdrive pulley set for our project Bronco. Follow along for a full report.

01. Having more power under the hood is always a fine thing in the sand. Actually, more power is a good thing in pretty much any environment.

02. Here is everything that is included in BBK’s Power-Plus underdrive pulley kit. The CNC-machined finish is quite attractive and should repel corrosion for some time to come. Less parts in a box can mean easier installations and less parts to lose—that was definitely the case here.

03. In fact, the only trouble we ran into at all was getting the stubborn nut off the alternator pulley as we started the installation. Be aware that these things are often difficult to remove! Here, two grown men try with all of their might to loosen the nut and end up looking like wimps.

04. Here are the installed pulleys after a weekend of use. These larger-than-stock pulleys dictate that the vehicle’s engine accessories will turn slower than they would than with stock pulleys. Additionally, they reduce the “moment of inertia,” which has to do with the power needed to cause motion and the distribution of mass being further away from the axis on which the pulley rotates. Simple translation: less parasitic power loss—the engine isn’t working as hard to drive the accessories. As you might imagine, aftermarket pulleys that aren’t designed correctly can cause the engine accessories to spin too slow, lessening their efficiency. That’s why it’s’ best to utilize a respected manufacturer like BBK.

05. After installing the pulleys for the first time, we realized that the stock drive belt would no longer be the length needed to fit around all of the engine accessory pulleys. We figured out what length was needed, and wrote down that length with a paint pen behind the grill of the Bronco so it would always be easy to reference.

06. Here’s the throttle body box and all of its contents. The BBK Power-Plus Twin 56mm throttle body is CNC-machined from 356 aluminum castings to ensure a perfect OEM-quality fit. OEM die-stamped throttle linkages, double sealed bearings, O-ringed throttle shafts, and a rugged frame combine to make this a somewhat sophisticated and robust part. This throttle body is designed to get the vehicle’s engine every bit of air that it can utilize in order to run as efficiently as possible. More usable air to the engine will mean more power.

07. The installation of BBK’s 56mm throttle body was pretty simple—it primarily involved removing the hose clamps from the stock unit, unbolting it, and replacing with the new stuff. One piece of info that can be helpful: in many vehicles, the fuel lines will remain pressurized even when the engine is not running, so if you decide to undertake a throttle body swap, be careful not to end up spraying your face with gasoline. This just may have happened to us at some point in the past…we’re not telling.

08. Here’s the old stocker throttle body we pulled off the Bronco. Eighteen years of use had taken its toll—check the corrosion on the inlet and outlet tubes on either side of the unit. BBK makes performance-oriented throttle bodies and underdrive pulley kits for most late-model vehicles (including a larger 61mm unit that would have also fit our Bronco). Check out their website (listed below) for a complete list of applications.

09. We had the Bronco in the sand just a few days after the underdrive pulley kit and throttle body were installed. Many times, when we install smaller-scale performance mods like these, it’s difficult to feel a power difference from the driver’s seat. In this case, we could actually feel some increased pep. And we’re happy to report that we didn’t detect a noticeable loss of efficiency from the A/C system, the alternator, or any of the other accessories driven by the engine pulleys and belt. It looks like we can chalk this up as a win/win.


BBK Performance
Temecula, CA 92590

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