General Motors' 4.3-liter V-6 is probably one of the most underrated engines ever built. Derived from the legendary Chevrolet small-block 350 and having powered what was, at the time, the two fastest pickups ever produced, this mighty mouse is nothing if not a tiny temple to tremendous potential. Building a 500-plus-horsepower 4.3-liter isn't quite as simple or cheap as screwing together a similarly powered small-block, but it's a doable project if you've got the time, budget and desire to do something different.
Start with a production Chevrolet 4.3-liter block and install four-bolt 350 main caps on the center journals. All 4.3-liters left the factory with two-bolt mains, but the center V-8 four-bolt caps will interchange with those on the V-6. Retrofit procedures are identical; install the caps, drill and tap the block for the additional bolts, secure all the mains with chrome-moly studs and have the block line bored to align the journals. GM performance did offer a Bow Tie race block cast for use with four-bolt mains and set up for dry sump oiling, but they were tremendously expensive when new and practically impossible to find now.
Select a rotating assembly. You've got two routes to go with here; you can either go with an off-the-shelf, steel, split-pin crankshaft and steel I-beam rods with 10.5-to-1 V-8 pistons, or a fully custom setup that will maintain your true even-fire firing order. The first approach is less expensive because while it does require an expensive V-6 crank, the rest of the parts are less costly 350 pieces. The 350 piston does use a slightly different wristpin offset, but it's useable in a 4.3-liter. The second approach, using custom parts to maintain your stock firing order, is far more expensive, but you'll end up with a smoother running and higher revving engine.
Bolt on a set of true Vortec cylinder heads, casting numbers 772, 113 or 140. Vortec heads will far outflow your stock heads right out of the box, but now is a good time to do some porting work for an extra 40 to 50 naturally aspirated horsepower. Use chrome-moly head studs and a gasket with an integrated sealing ring.
Choose your induction system. You've got three options for the intake: Use a ported 1996-later intake manifold if you want to keep the fuel injection; rework the bolt holes on the intake and heads to make the stock manifold fit; or chuck it all and buy an aftermarket carbureted manifold and carburetor. The first approach is fine if you've got the money, the second works if you're broke and don't mind making a few compromises and the third is probably the best all-around option if you want the engine to run.
Top off your motor with a set of equal-length headers sporting 1 7/8-inch primaries and 3-inch collectors, adjustable roller rocker arms and a 750 double-pump carburetor. A cam with about 238 degrees intake and 248 degrees exhaust at 0.050-inch lift, 0.520- and 0.540-inch valve and a 113-degree lobe separation angle should deliver between 340 and 350 horsepower with the carbureted setup -- a bit more with a multipoint fuel injected setup. While that's not bad, you may be thinking that this sounds like a lot of work for 350 horsepower. And you'd be right. That's why the last step is to...
Install a 200-horsepower plate nitrous system. Up to this point, you've built a fine anvil to contain the wrath of some sort of power adder. Turbochargers and superchargers are both fine options but require lower compression pistons, an intercooler and aftermarket fuel injection unless you want to go with a fuel-sucking and power-wasting Roots-type supercharger. A plate nitrous system and carburetor will easily deliver 500-plus reliable horsepower; more if you upgrade the system with propane injection instead of gasoline fuel enrichment. Propane runs about 110 octane, will act as a powerful intercooler in the intake and will absorb some of the combustion heat to enhance engine reliability. Add in propane injection and you could easily be looking at 550 to 600 horsepower from a stock-block V-6.
- Racing Engine Builder's Handbook; Tom Monroe
- Nitrous Oxide Injection Guide; Joe Pettit
- Hot Rod Magazine: 500 HP 4.3L Chevy V-6
- Hot Rod Magazine: Chevy 4.3L 262ci V-6 - The 3/4 350