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We've tested many of these parts in the past-particularly on 5.0 engines-and we've always had good luck with underdrive pulleys. So we were expecting a huge boost from the Auto Specialties pulleys here. Don't get us wrong, the pulleys made more power-2.3 ponies-at the peak, and pulled harder up top. However, they didn't give us the 10 hp or more we've seen on 5.0s. Rick says this is no fault of the pulleys; Ford has simply become more aggressive with its own pulley ratios to help power and fuel economy, so there's a less drastic change when adding underdrive pulleys. Of course, Rick is hoping to spin this engine 7,000 rpm and beyond. At that rpm, you definitely want underdrives to prevent overspinning your alternator and other drive accessories.