500hp 4.3L Chevy V-6

How to squeeze 500hp out of your 4.3L Chevrolet V-6 (hotrod.com)

500hp 4.3L Chevy V-6
-May 2007-

Question: I have a 4.3L V-6 Chevy engine. Will 350 Chevy rods and pistons fit in it? How strong is the stock block? Is there a four-bolt main block, or can I use splayed 350 caps? I would like an updated set of heads. Did GM make aluminum heads for this engine?

I saw a 3.75-inch stroker kit for the V-6. Is that a good idea? I also need a single-plane intake. I want to use aluminum rods in this engine to keep rotating weight down. I am going to run 12.5-13:1 compression. I’m not sure of a cam choice yet. I guess I could just cam it like a V-8, but I don’t know. I want to turn it 7,000-7,500 rpm and make 500 hp. It is going in an S-10 truck.

Nitrous is a possibility. When nitrous is rated at 200 hp for a V-8, how much is it for a V-6? I am shooting for mid-10s. Think it’s possible?
Michael Quesenberry
Leonardtown, MD

Answer: Whew-lots of questions here, but let’s take it from the top. Chevy’s production 4.3L 90-degree V-6 (V6-90) block is physically similar to a same-vintage 350 small-block V-8 with one important exception: the oiling system. Chevy small-block V-8s have three oil galleries above the camshaft. The central gallery feeds the camshaft and crankshaft bearings, while the two side galleries lubricate the lifters and valvetrain. Production V6-90 engines (including the 4.3) have only two oil galleries. The passenger-side gallery feeds the right bank of lifters, just like the small-block V-8. A large-diameter driver-side gallery feeds both the left lifter bank and the camshaft and crankshaft bearings; it is offset from the lifter bore centerline to allow oil to flow around the lifter bodies. The production V6-90 two-gallery oiling system has proven satisfactory through 7,000 rpm. In 1992, GM introduced a balance shaft on 4.3 engines.

All stock-production V6-90 blocks have two-bolt main caps. However, V-8 and V6-90 main caps interchange, permitting V-8-style four-bolt main caps to be installed on the center journals, just like they can be fitted to a two-bolt-main 350 block. New cap installation requires line-boring the block.

GM Performance Parts (GMPP) in the past has offered cast-iron, four-bolt-main, Bow Tie blocks through GM dealer parts departments. Some of these blocks also had full V-8 three-gallery oiling provisions, and depending on the specific part number, could be bored as large as 4.155 inches. Unfortunately, the blocks are no longer available new. Very pricey four-bolt-main, aluminum V6-90 blocks are still available from GMPP. They come set up for dry-sump oiling only and have no mechanical fuel-pump boss. PN 10134371 has standard 350 V-8-sized main journals; PN 10134351 has 400 V-8-sized main journals. They accept a 4.125-inch bore.

All production V6-90 heads are cast iron. Many V6-90s are called Vortec engines by GM, but not all have the good Vortec cylinder heads. The ’96-and-up V6-90 head should have the true Vortec-style kidney-bean chamber and vertical intake-manifold bolt pattern. It is essentially the 350 V-8 Vortec head minus one set of ports. According to the Cylinder Head Exchange, look for casting Nos. 772, 140, or 113. There’s about a 50/50 chance the 113 heads will be machined for fully adjustable rocker arms; the other casting numbers as well as the remaining 113s come with nonadjustable positive-stop rocker-arm studs. Crane Cams offers an adjustable conversion stud (PN 99148-2, six required), but for serious work, all these should be drilled and tapped for V-8-type screw-in rocker studs and roller rockers.

Brodix sells conventional, 23-degree valve-angle, aluminum V6-90 heads. PN V6-8 is for low-rpm, street-style engines. PN V6-10 is for large-cubic-inch, high-rpm engines. The heads use 2.08/1.60 valves, have 67cc chambers, and accept standard Chevy stud-mounted adjustable rocker arms.

Oiling System
The two-galley V-6 oil system (arrows) is OK through 7,000 rpm. In 1992, V6-90s got a balance shaft (sprocket, top) for smoothness. It creates additional inertial mass, not the plan for a serious hot rod, so delete it and plug any balance-shaft oil-feed holes. Don’t avoid ’96-and-up balance-shaft motors-most also have true Vortec heads.

Moving up the food chain, GMPP has offered various incarnations of Bow Tie aluminum heads for these engines, including high-port heads with conventional 23-degree valve angles, Rat motor-like splay-valve heads, and NASCAR-style 18-degree rollover heads. They really work best on 4.125-inch or larger cylinder bores (don’t bore a production block more than 0.030-over, to 4.030). At present, only the 18-degree heads are still available new. PN 10143359 is the older part; PN 12480009 features a new design of intake port for the Daytona Dash Racing series. These are serious heads that require Jesel shaft-mount valvetrains (or equivalent) and special pistons that match their competition-style, 43cc combustion chambers.

A production 4.3L V6-90 is a true even-fire engine. Achieving even firing pulses in a V-6 engine with a 90-degree cylinder-bank angle required GM to offset the connecting-rod throws 30 degrees to produce 120 degrees of crankshaft rotation between cylinder firings. Due to the journal offset, V6-90 rods as viewed from the side are narrower than V-8 rods, as are the rod-bearing inserts. V-8 rods and bearings won’t work on a production V6-90 even-fire crank. However, most aftermarket forged or billet race cranks use odd-fire cranks with common-pin (nonoffset) crankshaft rod journals. These will accept V-8 rods, although vibrations induced by the odd-fire cranks’ uneven firing impulses create considerable vibration on street-driven vehicles (that’s not a concern on a race car). Production V6-90 rods are satisfactory for high-perf and limited-production applications if they pass magnetic particle inspection, are properly rebuilt and polished, and are fitted with good ARP bolts. Custom even-fire V6-90 aluminum or steel rods are available from leading aftermarket suppliers. Although original even-fire V6-90 and small-block V-8 pistons have slightly different distances between the inner pin bosses, in practice, aftermarket forged-aluminum V-8 racing pistons can usually be used. Be sure to verify skirt clearance with the offset rod journals during trial assembly.

The distributor and camshaft firing sequence must match the crankshaft (even-fire with offset rod journals or aftermarket common-pin odd-fire). The ’92-and-later balance-shaft engines require yet another cam core and unique timing set. MSD offers billet distributors. Some ’85 4.3L even-fire V-6 engines with federal emissions had a large-cap HEI distributor that still retained conventional mechanical and vacuum-advance provisions (NAPA remanufactured PN NRD481685, Hollander Salvage Yard Interchange No. 2221).

When it comes to race-type intake manifolds, the two-piece GM cross-ram intake that fit its now-discontinued 23-degree raised-runner aluminum heads is the only one currently available. It won’t fit Vortec heads, 18-degree rollover heads, or splay-valve heads. Edelbrock offers V6-90 Performer low-rise dual-planes (PN 2111 for heads with traditional angled bolts or PN 2114 for true Vortec heads with vertical intake-manifold attaching bolts). There is no Performer RPM or Victor Jr.-style intake available. Most V6-90 racers use fabricated sheetmetal intakes.

A 200hp V-8 plate nitrous kit should still make 200 hp on a V-6 because it retains the same jets calibrated with the proper oxygen/fuel/nitrous ratio to maintain 200 hp. In other words, a plate system is a constant mass-flow system. On the other hand, a direct-port nitrous system (each manifold port has its own dedicated nitrous and fuel nozzles) would be down 25 percent on a V-6 compared with a similar V-8 system because it has 25 percent fewer nozzles.

Can a V6-90 be built to run mid-10s? Let’s look at the parameters. Figure on your S-10 weighing about 3,000 pounds in race trim (including fuel and driver). With a fairly decent chassis and drivetrain, 500 hp should be sufficient to run 10s. Assuming a 4.030-inch bore x 3.75-inch stroke, you’re looking at a 287ci engine (three-quarters of the popular 383 small-block). You’d have to develop 1.74 hp/ci to make 500 hp on 287 ci, mandating a pretty high-level buildup to do it all motor with no power-adders. That also means expensive (and often hard-to-obtain) Bow Tie parts. But with a 150hp nitrous shot, you’d only need to make 350 hp on the motor, about 1.22 hp/ci. That’s more reasonable and should be possible using massaged, production-based parts.

So . . . start with a production block. Install V-8 four-bolt main caps and stud the bottom end. The crank would be the stroker you saw, but I’d go with aftermarket steel rods. Aluminum rods have a finite fatigue life and aren’t really needed because you won’t be revving the snot out of the motor. Use good, aftermarket, forged, custom-made pistons. Install a hydraulic roller camshaft with 235-240 degrees duration at 0.050. You’ll already have roller lifters from your good core engine. Comp Cams’ Nitrous HP NX288R grind (236/248 degrees at 0.050, 0.520/0.540 valve lift, 113-degree lobe separation) is optimized for nitrous oxide. It would be a custom grind for a V6-90. The exact specs vary slightly, depending on whether the engine is odd- or even-fire, has or doesn’t have a balance shaft, and/or if a reduced base circle is needed to clear the stroker crank’s rods (another reason for more compact steel rods). The ’96-and-later Vortec heads-when mildly pocket-ported and using fully adjustable roller rocker arms-are affordable and up to the task. If you want to splurge, move up to the Brodix aluminum heads, but I’d save my dough for a good sheetmetal Wilson intake manifold and custom headers with 1-7/8-inch primaries x 3-inch collectors (or even stepped primaries). In any event, feed the engine with a 750 double-pumper carb. That’ll get you to around 340-350 hp. Then bolt on a 200hp plate nitrous system and you’re there, with a slight cushion.

Another option is to use the 4-71 Roots blower kit from Blower Drive Service or to add a Vortech blow-through centrifugal kit as we did to build a 500hp 4.3; see the story in the Technical Articles archive on www.HOTROD.com.

Blower Drive Service
Whittier, CA
Brodix Cylinder Heads
Mena AR
Comp Cams
Memphis, TN
Crane Cams
Daytona Beach, FL
Torrance, CA
GM Performance Parts
Warren, MI
MSD Ignition
El Paso, TX
NAPA Auto Parts
Atlanta, GA
Wilson Manifolds
Ft. Lauderdale, FL

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