Based on the 350 small-block V-8, the "three-quarter small-block," 4.3-liter has proven a surprisingly long-lived design. That's especially true when you consider the fact that the 4.3-liter, unlike its similarly V-8 derived Buick 3.8-liter cousin, was almost an afterthought in the engineering department at GM. Time marches on, though, and the 4.3-liter has built quite a reputation for performance, based on its family relations.
When people say that the 4.3-liter is a 350 with two middle cylinders left out, that's not just an ideological observation; most of the parts that don't run lengthwise between the two engines will swap from one to the other. That's especially true for very early engines, like those from the 1985 model year, which actually debuted in 1984. These early engines came with either a simple throttle-body injection system or a Rochester carburetor, and lacked the decades of evolution that moved the 4.3-liter gradually away from its 350 roots. When you're looking at supercharging early 4.3-liters, you need not look much further than supercharger kits designed for the same-year 350 V-8.
You can broadly separate superchargers in one of two types: "positive displacement" superchargers that bolt to the top of the engine, and "centrifugal" superchargers that bolt to a bracket on the front like an alternator. Positive displacement kits are plenty and cheap for small-blocks, but as of 2013 you're not going to find a bolt-on PD kit for the 4.3-liter. Nobody makes a manifold to bolt the supercharger to the engine, so you're stuck either cobbling a manifold together yourself, or paying $1,000 or more to have one custom-built for you. A positive-displacement supercharger will give you more response off the line, but it's just not worth the money and aggravation when there are simpler options available.
With only a few minor modifications to the intake plumbing, any centrifugal supercharger kit designed to fit the classic small-block 350 will bolt onto the 4.3-liter. The two engines use exactly the same accessory drive systems and pulley configurations, so there's no problem swapping one centrifugal to the other as long as it was designed for the carburetor or throttle-body injection system that your particular engine came with. Hot Rod magazine proved exactly that in February of 2009, when they took the Vortech S-Trim supercharger off of their 675-horse HT383 crate engine V-8 and bolted it directly to a 4.3-liter V-6. The result: 501.4 horsepower at 6,200 rpm and 434 foot-pounds of torque at 5,500 rpm.
An entry-level Vortech supercharger kit will run you about $2,200. Like most kits along these lines, it fits a Holley 4150-style carburetor flange and carburetor. You could hypothetically squeeze it onto your existing Rochester-pattern manifold with an adapter, but you might as well spend $200 on an aftermarket manifold like those made from Edelbrock. You might be inclined to keep the fuel injection system, but you're going to put a lot of time and money into modifying it for supercharged power levels, versus buying a $500-to-$700, boost-referenced, Holley-4150-flanged carb designed specifically for supercharged duty. You can spend upward of $4,300 for a kit equivalent to the Vortech YSI-trim -- however, this blower's 1,200-horse capacity might be a little on the high side for a factory block.
